建構兆位元紀元的光電科技---子計畫一：兆位元時代光電科技之基礎研究(IV)

※大學學術追求卓越發展延續計畫執行報告格式

Explanation for the Form of the Annual/Midterm/Final Report “Program for Promoting

Academic Excellence of Universities（Phase II）”

※ The Annual/Midterm/Final Report contains the following sections:

I COVER 1

II FORM1 BASIC INFORMATION OF THE PROGRAM 2

III FORM2 LIST OF WORKS,EXPENDITURES,MANPOWER, AND MATCHING SUPPORTS FROM THE

PARTICIPATING INSTITUTES（REALITY）. 3

IV FORM3 STATISTICS ON RESEARCH OUTCOMES OF THIS PROGRAM 4

V FORM4 EXECUTIVE SUMMARY ON RESEARCH OUTCOMES OF THIS PROGRAM 6

VI APPENDIX I MINUTES FROM PROGRAMDISCUSSION MEETINGS 46

VII APPENDIX II

1. PUBLICATION LIST (CONFERENCES,JOURNALS,BOOKS,BOOK CHAPTERS,etc.）

2. PATENT LIST

3. INVENTION LIST

4. LIST OF WORKSHOPS/CONFERENCES HOSTED BY THE PROGRAM

5. LIST OF PERSONAL ACHIEVEMENTS OF THE PIS

6. LIST OF TECHNOLOGY TRANSFERS

7. LIST OF TECHNOLOGY SERVICES

47

VIII APPENDIX III LIST OF PUBLICATIONS IN “TOP”JOURNALS AND CONFERENCES 102

IX APPENDIX IV S_BREAKTHROUGHLIDES ON SCIENCE AND ₎ TECHNOLOGY BREAKTHROUGHS (TWO SLIDES FOR EACH 104

X APPENDIX V SELF-ASSESSMENT 108

I. COVER

Program for Promoting Academic Excellence of Universities（Phase II）

Final Report

建構兆位元紀元的光電科技-子計畫一：兆位元時代光電科技之基礎研究 Photonic Sciences and Technologies for the Tera Era:

Subproject 1: Fundamental Studies on Photonic Science and Technology for the Tera Era NSC 93-2752-E-009-008-PAE

NSC 94-2752-E-009-007-PAE NSC 95-2752-E-009-007-PAE NSC 96-2752-E-009-007-PAE

Overall Duration: Month 4 Year 2004 - Month 3 Year 2008 Report Duration: Month 4 Year 2004 - Month 3 Year 2008

National Chiao Tung University 2008.05.02

2

II. (FORM1)BASIC INFORMATION OF THIS SUB-PROJECT (FORM2)

Project Title: Photonic Sciences and Technologies for the Tera Era--Subproject 1:

Fundamental Studies of Photonic Science and Technology for the Tera-era 建構兆位元紀元的光電科技-子計畫一：兆位元時代光電科技之基礎研究

Serial No.: NSC 94-2752-E-009-007-PAE Affiliation National Chiao Tung University 國立交通大學

Name Ci-Ling Pan

潘犀靈 Name Hao-Chung Kuo 郭浩中 Tel: (03)5712121-31921 Tel: (03)5712121-31986 Fax: (03)5716631 Fax: (03)5716631 Princ ipal I n ves tigator

E-mail [email protected] Project Coo

rdinator

E-mail [email protected] Expenditures1 _{(in NT$1,000) Manpower}2_{:Full time/Part time(Person-Months)}

Projected Actual Projected Actual

FY2004 11,786 11,786 50 50

FY2005 12,947 12,947 50 50

FY2006 12,948 12,948 50 50

FY2007 13,446 13,446 50 48

Overall 51,127 51,127 200 198

Notes: 1,2 _{Please explain large differences between projected and actual figures.}

III. (FORM 2) LIST OF WORKS, EXPENDITURES, MANPOWER, AND MATCHING SUPPORTS FROM THE PARTICIPATING INSTITUTES（REALITY）. 96 年度

Serial No.: Program Title: (in both English & Chinese)

Expenditures (in NT$1,000) Manpower (person-month) Research Item

(Include sub projects)

Major tasks and

objectives _Salary Seminar/ Conference-relate d expenses Project- related expenses Cost for Hardware & Software Total Principal Investigators Consultants Research/ Teaching Personnel

Supporting Staff Total

Matching Supports from the Participating Institutes (in English & Chinese) Generation of coherent infrared radiation 1802 396 1572 583 4353 4 4 Population-split genetic algorithm 1925 380 2008 561 4874 4 16 20 Near-infrared fs laser crystallized polycrystalline silicon TFT 1969 423 1157.6 589.3 4138.9 8 28 36 A powerful THz emitter in the 800nm wavelength regime 1824 350 1550 498 4222 8 20 28 All-Optical Nework Components 1699 380 1410.2 563 4052.2 4 12 16 High-Speed Optical Receivers 2000 372 10010 568 12950 4 24 28 GaN-based a Light Emitting Diodes 1903 408 1291.2 569 4171.2 4 16 20 GaN-based VCSEL _{1703 411.7 940 521} 3575.7 4 16 20 Photonic Crystal Microcavity Lasers 2045.9 402.3 1664 601 4713.2 4 14 20 Fundamental Studies on Photonic Science and Technology for the Tera Era

the optimization of our doped PMMA

photopolymers 1826.7 446 912.4 583 3768.1 8 8

4

IV. (FORM 3) STATISTICS ON RESEARCH OUTCOME OF THIS PROGRAM 96 年度

LISTING TOTAL DOMESTIC INTERNATIONAL SIGNIFICANT1 CITATIONS2 TECHNOLOGYTRANSFER

JOURNALS 257 0 242 15 CONFERENCES 389 171 186 32 PUBLISHED ARTICLES TECHNOLOGY REPORTS 0 0 0 0 PENDING 1 1 0 0 PATENTS GRANTED 22 14 8 0-

COPYRIGHTED INVENTIONS ITEM 0 0 0 0 0

ITEM 41 16 25 0

WORKSHOPS/CONFERENCES3

PARTICIPANTS 41 16 25 0

HOURS 0 0 0 0

TRAINING COURSES

（WORKSHOPS/CONFERENCES） PARTICIPANTS 0 0 0 0

HONORS/AWARDS4 18 11 7 0

KEYNOTES GIVEN BY PIS 1 0 1 0

PERSONAL ACHIEVEMENTS

EDITOR FOR JOURNALS

4 0 4 0 ITEM 3 3 0 LICENSING FEE 1,000,000+ 1,000,000+ 0 TECHNOLOGY TRANSFERS ROYALTY 0 0 0 0

INDUSTRY STANDARDS5 ITEM 0 0 0 0 0

ITEM 0 0 0 _{- - -}

TECHNOLOGICAL SERVICES6

SERVICE FEE 0 0 0 - - -

1 _{Indicate the number of items that are significant. The criterion for “significant” is defined by the PIs of the program. For example, it may refer to Top journals (i.e., those with impact factors in the upper 15%) in the area of research, or}

conferences that are very selective in accepting submitted papers (i.e., at an acceptance rate no greater than 30%). Please specify the criteria in Appendix IV.

2 _{Indicate the number of citations. The criterion for “citations” refers to citations by other research teams, i.e., exclude self-citations.} 3 _{Refers to the workshop and conferences hosted by the program.}

4 _{Includes Laureate of Nobel Prize, Member of Academia Sinica or equivalent, fellow of major international academic societies, etc.} 5 _{Refers to industry standards approved by national or international standardization parties that are proposed by PIs of the program.}

6

V.(FORM4) EXECUTIVE SUMMARY ON RESEARCH OUTCOMES OF THIS PROGRAM

(PLEASE STATE THE FOLLOWING CONCISELY AND CLEARLY)

1.

G

D

P

:

I

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(M

3

)

The main goals of this project are to design, construct and characterize new optical and

optoelectronic functional devices and modules to meet the challenge of the tera-bit information era.

To achieve these goals, we focus our research on the following fundamental research topics:

(I)

Coherent and THz Photonics;

(II)

Quantum (Photonic Crystal) structures and Enabling devices;

(III) Volume Holographic Materials, Technology and Enabling devices

(I) Coherent and THz Photonics

One of the current trends in photonics is the development of a technology based with better

control of the light-matter interaction. Employing advanced laser-based techniques, novel design

concept, and fabrication technologies of novel photonic structures from potential photonic

materials, we shall be able to steer photon energies into specific degrees of freedom of complex

systems or materials, to create new materials, to generate new functionality from a device. One of

the goals of the present project is thus the development and employment of advanced laser

technology, in particular, ultrafast-laser-based techniques such as coherent control, spatially,

temporally, and spectrally resolved real-time imaging, and laser-assisted fabrication and properties

modification for fundamental studies of photonic properties of various novel photonic materials,

structures and devices.

In view of the emerging applications of electromagnetic waves at millimeter-wave or THz

frequencies in remote sensing, imaging, and communication, we will conduct studies on various

aspects of THz photonics and applications, employing the coherent photonic tools developed in our

laboratories over the years.

One of our main objectives is the building a technology base of photonics-based

ultra-wideband (THz) wireless communication and frequency measuring technologies for the next

generation. The advances in THz applications would also require concurrent progress in THz

photonic elements, such as generators, detectors, polarizers, attenuators, modulators and phase

shifters. Novel materials and structures need be explored to address this requirement. Topics

include (1) highly efficient THz emitters and detectors, (2) exploration of the possibility of

combining liquid crystals with photonic crystals and meta-materials for tunable THz optics. With

the structured material or meta-material and highly birefringent materials such as liquid crystals for

added functionality, new possibilities arise for novel optical elements because of the strong

coupling of these novel materials with the electromagnetic wave. Starting from the theoretical

analysis, we will work on design and fabrication of various THz optical components. Our

long-range goal would be highly directional and intense THz sources, taking advantage of the

unique properties of photonic crystals or meta-materials. The technologies developed in this project

would also make possible advances in other important applications of THz science and technology,

e.g., biomedical sensing and imaging.

(II) Quantum (Photonic Crystal) structures and Enabling devices

The main objectives of this research project will be focus on 3 parts. First, Development and

study of novel blue and UV-LED and surface emitting laser, the specific objectives of this proposal

include (1) to development nitride-based blue and UV material and optoeletronic device; (2) to

development novel process for obtaining high performance of blue and UV LED and LD. Second,

to investigate nanotechnology and nano-photonics. This part of the object will focus on

investigating the optical properties of mesoscopic GaN-based quantum confined structures and to

achieve controlled photon emission from the GaN-based quantum confined structures. The specific

objectives of this proposal include (1) establishment of the fabrication technology of GaN quantum

confined structures such as quantum dots and nanostructures; (2) simulation and modeling of the

op;tical properties of microcavity quantum confined structures and development of device design

guidelines for fabrication of microcavity quantum confined structures; (3) fabrication of devices

that incorporate the quantum confined structures into a microcavity such as vertical cavity surface

emitting laser (VCSEL) structures; (4) investigation of the optical properties of the fabricated

quantum confined structures and microcavity structures; and (5) investigation and demonstration of

the controlled photon emission from the microcavity quantum confined structures or devices.

Third, for the fabrication of long wavelength VCSEL (LW-VCSEL) and high speed VCSEL for

communication, the specific objectives of this proposal include (1) fabrication single mode high

speed GaAs or InP -based VCSEL; fabrication of InP based 1300 nm or 1500nm Long Wavelength

VCSEL; (2) VCSEL Arrays Chip and Multiple-Wavelength or tunable Source.

- The GaN-based UV LD have applicatics to the high density storge in the storge project..

- The Long Wavelength VCSEL will be useful to the optical communication project.

(III) Volume Holographic Materials, Technology and Enabling devices

Volume holographic technology and applications have been explored for past 50 years but still

have not yet achieved significant breakthrough. The development of the proper recording material is

a fundamental key to the success for the holographic systems. Therefore, in this sub-project, we

plan to develop novel volume holographic materials and explore its applications on novel

information processing with ultrahigh density (1 Tbits/in2) and ultrafast fast (Tbps). Through the

innovative researches and international collaborative efforts, we anticipate becoming a world class

leader in the field of parallel information photonic system.

8

2.

B

M

A

1. Advanced laser technology and applications

In collaboration with Prof. Andy H. Kung, we have developed novel spatial light modulators

that enable generation of Sub-Single-Cycle (0.83 cycles long and an electric field pulse width of 0.

44 fs) optical pulse train with constant carrier envelope phase by molecular modulation in H2.

[Phys. Rev. Lett. 100:163906, 2008]. Major achievements in ultrafast fiber lasers include report of

self-steepening of prechirped amplified and compressed 29-fs fiber laser pulse in large-mode-area

erbium-doped fiber amplifier [OSA/IEEE J. Lightwave Technol., 25(11): 3597, 2007]. We also

showed that femtosecond laser annealing (FLA) as a novel approach for recrystallization of

amorphous silicon (a-Si) for TFT applications [reported at CLEO2003 as a news story; APL

85(7):1232, 2004, selected by the Virtual Journal of Ultrafast Science, September 2004, ROC patent

I245321], dopant profile engineering [APL 88:1311104, 2006, selected by Virtual J. of Nanoscale

Sci. and Technol., and Virtual J. of Ultrafast Sci.]. Laser-recrystallized material was used

successfully for fabricating thin film transitors [

Opt. Exp., 15: 6981, 2007

, selected by Virtual J. of

Ultrafast Sci.].

2. THz photonic elements with liquid-crystal-enabled functionalities

We have pioneered this field. The optical constants of several important liquid crystals were

determined in the THz regime for the first time. Unexpected large birefringence was observed for

the liquid crystals 5CB and E7 in the nematic phase. These properties were utilized to demonstrate

both magnetically and electrically controlled THz phase shifters, culminating in the first

room-temperature, 0-2

π

tunable THz phase shifter [Opt. Exp. 12(12): 2625, 2004, Selected by the

Virtual Journal of Ultrafast Science, September 2004, Taiwan Patent 200186, US patent filed]. The

device operates at room temperature, as opposed to previous devices needing liquid N2 for cooling

and achieving phase shift of a few degrees at best. Important applications such as THz phased

arrayed radar would be possible. Our work on THz photonic elements with liquid-crystal-enabled

functionalities was highlighted by SPIE Newsroom (http://spie.org/x14608.xml).

3. Highly efficient Blue LED and Electrically pumped GaN VECSEL

We report the first ever electrically pumped GaN VCSEL. The laser, which has the potential

to be used in high-density optical storage and laser printing applications, produced continuous-wave

462 nm emission with a linewidth of 0.15 nm at 77K. Details of the device, the culmination of eight

years of VCSEL development [Appl. Phys. Lett. 92:141102, 2008, reported by Compound

Semiconductors Magazine, April 2008]. We have also demonstrated high light-extraction

(external quantum efficiency ~40%) 465-nm GaN-based vertical light-emitting diodes (LEDs)

employing double diffuse surfaces. The high scattering efficiency of double diffused surfaces could

be responsible for the high light output power. The calculated external quantum efficiency of our

proposal LEDs with double diffuse surfaces is about 40% at 20mA (λ ~ 465 nm), which could

compete with structures of state of the art.

We successfully improved the performance of LEDs using two methods:

(1) Enhancement of flip-chip light-emitting diodes with Omnidirectional reflector and textured micropillar arrays The light output power of the FC-LED was increased by 65% for a 3.2-μm textured micropillar on the bottom side of the sapphire substrate

(2) High Light-Extraction GaN-based Vertical LEDs With Double Diffuse Surfaces

The calculated external quantum efficiency of our proposal LEDs with double diffuse surfaces is about 40% at 20mA (λ~465 nm), which could compete with structures of state of the art.

(3) Fabrication and Characterization of GaN-based LEDs Grown on Chemical Wet-etched Patterned Sapphire Substrates (CWE-PSS)

(4) Trenched epitaxial lateral overgrowth of fast coalesced a-plane GaN with low dislocation density

We have grown high quality and fully coalesced a-plane GaN films at the thickness of 10 μm by using trenched epitaxial lateral overgrowth (TELOG) with a 2 μm seed/18 μm trench stripe pattern

(5) Enhancement of light output intensity by integrating ZnO nanorod arrays on GaN-based LLO vertical LEDs The light output intensity and wall-plug efficiency of the GaN-based LLO vertical LED with the omnidirectional extraction surface by ZnO nanorod arrays shows 38.9 and 41.2% increases, respectively, at 200 mA current injections compared to that of a vertical LED without ZnO nanorod arrays

(6) High-Performance GaN-based vertical-injection light-emitting diodes with TiO2–SiO2 Omnidirectional reflector

and n-GaN roughness

With the help of laser lift-off and photo-electrochemical etching technologies, at a driving current of 350 mA and with chip size of 1 mm × 1 mm, the light–output power and the external quantum efficiency of our thin-film LED with TiO2–SiO2 ODR reached 330 mW and 26.7%. The result demonstrated 18% power enhancement when compared with

the results from the thin-film LED with Al reflector replace.

(7) Study of high reflectivity mirror for blue high quality light emitter

Using a crack-free GaN/AlN DBR incorporated with GaN/AlN superlattice (SL) layers was successfully grown on a c-plane sapphire substrate to achieve high quality light emitter.

1. Development and study of nanotechnology, nano-photonics, and surface emission laser

(1) InGaN/GaN nanostripe grown on pattern sapphire by metal organic chemical vapor deposition

These MQW nano-stripe arrays are capable of enhancing luminescence and appear to be suitable for application to the fabrication of high-efficiency light-emitting devices.

(2) Successfully achieved the Lasing Action of GaN-based Two Dimensional Surface-emitting Photonic Crystal Laser The lasing wavelength located at 424.3 nm, and the FWHM of the laser is around 0.11 nm. Other devices also could be observed the lasing actions occur at the similar threshold energy but different lasing

(3) Fabrication of InGaN/GaN MQW Nanorods LED by ICP-RIE and PEC Oxidation Process with Self-Assembly Ni Metal Islands

An enhancement by a factor of 6/5 times in photoluminescence intensities of nanorods with/without PEC process compared to that of as-grown structure. The peak wavelength observed from PL measurement shows a blue shift of 3.8 nm of the nanorods without PEC oxidation process and 8.6 nm of the nanorods with PEC oxidation process from that of the as-grown LED sample.

10

3. Development and study of blue VCSEL

(1) Study of high Q micro-cavity light emitting diode (MCLED)

The MCLED shows that the emission intensity superlinearly increased with a very narrow linewidth of 0.52 nm equivalents to cavity Q value of 895 at driving current of 10 mA and a dominant emission peak wavelength at 465.3 nm (2) Emission characteristics of optically pumped GaN-based vertical-cavity surface-emitting lasers

The laser emitted wavelength at 415.9 nm with an emission linewidth of 0.25 nm and threshold pumping energy of 270 nJ. The laser has a high characteristic temperature of about 278 K and high spontaneous emission coupling factor of 10−2. The laser emission showed single and multiple spot emission patterns with spectral and spatial variations under different pumping conditions.

(4) Study of characteristics of GaN vertical cavity surface emitting laser (VCSEL)

The GaN VCSEL emits a blue wavelength at 448 nm with a linewidth of 0.17 nm with a near-field emission spot diameter of about 3μm. The laser beam has a near linear polarization with a degree of polarization of about 84%. (5) Successfully fabricated low-temperature electrical pumping InGaN-MQW VCSELs by hybrid mirrors

The center wavelength is at 465nm and a distinct narrow linewidth of the peak is nearluy 5.2Å which can be calculated the cavity quality factor (Q) about 894

First Electrical

Pumping VCSEL Results

4. Utra-low shrinkage holographic photopolymer

We have fabricated high-optical-quality large photoplymer disk (120mm diameter, 2mm thick)

and bulk (2.5×4.0×10.0 cm

_{) samples for volume holographic storage. [J. of Non. Opt. Phys. and}

Mats., Vol. 15(2), 239, 2006;

ICO book Chapter, in press, 2008

.] This photopolymer exhibits

negligible shrinkage effect during holographic recording. Sub-tera-byte capacity (~450GB) was

demonstrated for a 5-inch disk. The physical mechanism of holographic recording in doped PMMA

has also been investigated and provides hints to improve holographic properties. [Opt. Communs.,

281, 559-566, 2008] Further, we have developed world's first Fe, Ru, Mn, doped Bi4Ge3O12

photorefractive crystals for Red and NIR holographic recording. [Opt. Communs., 37-43, January

2008.] By use of our thick recording materials, we have also developed volume holographic

technology for measuring 3D-fluid flow fielding micro-channel. [J. Optical Memory & Neural

Networks, Vol., 14 (2), 129-135, 2006.]

12

3. C

S

R

O

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I

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.

N

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P

A

II,

A

III.

A.

C

TH

P

Profs. Ci-Ling Pan, Ru-Pin Chao Pan, Jung Y. Huang, Gong-Ru Lin and Jin-Wei Hsu

Major research outcomes in this area include generation of sub-single-cycle optical pulses,

adaptic coherent control, dipole antennas with detection bandwidth exceeding 30 THz, a record for

ion-implanted photoconductors (OptExp’04, selected by the AIP virtual journal), first

directly-modulated THz communication link for audio and burst signals (Opt Exp’05). Prof. Pans’

group also pioneered the field of Liquid Crystal THz Photonics, achieving the first

room-temperature, 0-2π tunable THz phase shifter [OptExp04, selected by the AIP Virtual Journal,

Taiwan Patent 200186, US patent pending], an important milestone for THz phased array

applications. The work on other liquid-crystal-enabled THz functional devices such as a tunable

THz Lyot filter (APL’06, Taiwan and U.S. patents pending) was highlighted by SPIE Newsroom

(

http://spie.org/x14608.xml

).

In collaboration with ITRI, the NCTU team has developed a THz

System for Detecting of biological tissue burn trauma (Taiwan patent I276425, U. S. patent

7307258 B2). In collaboration with Prof. Jin-Wei Shi, Prof. Pan and co-workers have developed

high-speed optical detectors and THz photonic transmitters with bandwidth beyond several hundred

GHz (APL’06, PTL’07, PTL’08). In collaboration with Prof. Chi-Kuang Sun (NTU), we have

reported low-loss hollow-core THz fiber wave guide [APL’08, highlighted by Nature Photonics,

April 2008]. Scanning and interferometric THz fiber endoscopic imaging was also demonstrated

(APL’08, OptExp’08).

1.

Ultrabroad band THz field detector based on Arsenic-ion-implanted GaAs and

proton-bombarded InP (Prof. Ci-Ling Pan):

A detection bandwidth exceeding 30 THz was reported for THz dipole antenna fabricated on

InP:H

[Opt. Exp. 12(13):2954, 2004, selected by the Virtual J. of Ultrafast Sci., August 2004].

This is an extension of our previous work on Arsenic-ion-implanted GaAs [APL 83(7)1322, 2003,

selected by the Virtual J. of Ultrafast Sci., September, 2003]. Both types of devices exhibit the

broadest bandwidth reported for THz antennas based on ion-implanted photoconductors and

comparable to that of LT-GaAs, the current state-of-art material for such applications. A

photoconductive THz Spiral Antenna fabricated on multi-Energy Arsenic-Ion-Implanted GaAs also

was well-received [JAP 98:013711, 2005. Selected by the Virtual J. of Ultrafast Sci., August 2005].

Such antennas were used for the first directly-modulated THz communication link for audio and

burst signals (Opt Exp 13, 10416-10423, 2005) In collaboration with ITRI, the NCTU team has

developed a THz System for Detecting of biological tissue burn trauma (Taiwan patent I276425, U.

S. patent 7307258 B2).

2. Novel Photonic THz Transmitters (Profs. Jin-Wei Shi and Ci-Ling Pan)

We have investigated two types of sub-THz Photonic-Transmitters. The first design is

based on Separated-Transport-Recombination Photodiodes (STR-PD) based on low-temperature

MBE-grown GaAs (LTG-GaAs) and a Micromachined Slot Antenna [PTL 19:840, 2007]. Under

femtosecond optical pulse illumination, this device radiates strong electrical pulses (4.5-mW peak

power) without the use of a Si-lens. The peak power is as high as 300 μW, occuring at 500 GHz,

which corresponds to the designed resonant frequency of the slot antenna. The saturation problem

14

related to the output terahertz power that occurs with the traditional LTG-GaAs-based

photonic-transmitters when operated under high external applied electrical fields ( 50 kV/cm) has

been eliminated by the use of our device.

An alternative design, appropriate for wireless THz impulse-radio (IR) communication, is

realized by monolithic integration of a GaAs/AlGaAs based uni-traveling-carrier (UTC) photodiode

with a substrate-removed broadband antenna. The device can radiate strong sub-THz pulses (20mW

peak-power) with a narrow pulse-width (<2ps) and wide bandwidth (100~250GHz). The

maximum average power emitted by our device, under the same THz time-domain spectroscopic

setup, is around 10 times higher than that of the low-temperature-grown GaAs based

photoconductive antenna, whilst with a much lower DC bias (9V vs. 35V). [PTL, to appear 2008].

3.

Liquid crystal THz photonics (Prof. Ci-Ling Pan and Ru-Pin Pan)

We have pioneered this field. The optical constants of several important liquid crystals

were determined in the THz regime for the first time [Appl. Opt., 42(13): 2372, 2003 and J.

Biological Phys. 29(2-3):335, 2003, J. Appl. Phys.

103: 101809, 2008, Ferroelectrics, to appear

2008]. Unexpected large birefringence was observed for the liquid crystals 5CB and E7 in the

nematic phase. These properties were utilized to demonstrate both magnetically and electrically

controlled THz phase shifters [APL 83(22): 4497, 2003; IEEE MWCL 14(2):77, 2004,], culminating

in the first room-temperature, 0-2

π

tunable THz phase shifter [Opt. Exp. 12(12): 2625, 2004,

Selected by the Virtual J. Ultrafast Sci., September 2004, Taiwan Patent 200186, US patent filed].

The device operates at room temperature, as opposed to previous devices needing liquid N2

for

cooling and achieving phase shift of a few degrees at best. Important applications such as THz

phased arrayed radar would be possible. Recently, we also reported control of enhanced THz

transmission through 2-D metallic hole arrays using magnetically controlled birefringence in a

nematic liquid crystal cell. [Opt. Exp. 13(11): 3921, 2005, collected by the Nanostructured Surfaces

Web]. The first ever THz Lyot filter [APL 88:101107, 2006, collected by the Virtual J. of THz Sci.

and Technol.], electrically switchable THz quarter-wave plate [OL 31(8):1112, 2006, collected by

the Virtual J. of THz Science and Technology, OSA Virtual J. Biomed. Opt.] and electrically tunable

room-temperature 2π Liquid Crystal Terahertz Phase Shifter [IEEE PTL 18(14): 1488, July 15,

2006, collected by Virtual J. of THz Sci. and Technol., July 2006] were demonstrated recently.

Our work on THz photonic elements with liquid-crystal-enabled functionalities was highlighted by

SPIE Newsroom (http://spie.org/x14608.xml) in 2007. Other novel devices such as polarizers, phase

gratings, Solc birefringent filters have also been demonstrated [OL, to appear 2008, Opt. Exp.

16(5):2995, 2008; OL, to appear 2008].

16

4.

Adaptive coherent control: Technology and Applications (Profs. Jung Y. Huang, Chuck

Chao-Kuei Lee and Ci-Ling Pan)

A freezing phase concept has been proposed for adaptive coherent control with a femtosecond

pulse shaper [JOSA B 22:1134 (2005), selected by the Virtual J. Ultrafast Sci., 2005]. The

operational principle is based on a concept that the highest peak intensity will correspond to a

frozen phase state of all spectral components involved in a coherent optical pulse. It is fast and

immune to the noise and laser power fluctuation, and useful for a variety of applications that require

complete-field characterization and adaptive coherent control on the same setup. We applied the

scheme to investigate multiphoton processes in InAs quantum dot saturable Bragg reflector (SBR,

fabricated by Prof. Jen-Inn Chyi, NCU). The optical transition of InAs quantum dots can be

revealed in the spectral phase sensitivity plot of second harmonic signal. We also achieved a

three-time increase in image contrast on regions with photoluminescent wavelength differing only

18 nm by using coherent control nonlinear optical microscopy.

Emplying the freezing phase algorithm, we also investigated the enhancement of broadband

THz radiation using femtosecond pulse shaping. Over 60% radiation enhancement in output

power and two-fold broadening of bandwidth were found for optimized positively chirped optical

pulses. We have tentatively attributed the phenomon to the increasing saturation fluences from

competition between band-filling and pump-dump processes during excitation. In addition, pump

power dependence of THz radiation and enhancement factor, which is defined as ratio of peak

amplitude of the radiated THz pulse before and after adaptive control. With fixed probe beam

power while reducing the pump power from 45mW to 5mW, we observed an increase in the

enhancement factor from 40% to 60%. A model of enhancement based on higher saturation

flurence for positively-chirped optical excitation is proposed. Other factors such as difference in

absorption by leading waves in for positive or negative chirped pulse could also contribute to the

observed phenomenon [CLEO’08, Opt. Exp., submitted, 2008]. .

5.

Femtosecond LaserAnnealing: A novel approach for dopant profile engineering and

fabrication of poly-Si TFT (Prof. Ci-Ling Pan)

Amorphous silicon (a-Si) for TFT applications was crystallized by femtosecond laser

annealing (FLA) using a near-infrared (800 nm) ultrafast Ti:sapphire laser system for the first time.

We found that FLA assisted by spatial scanning of laser strip spot can crystallize a-Si films with

largest grains of ~800 nm, requiring laser fluence as low as ~45 mJ/cm2, and low laser shots.

Moreover, the optimal annealing conditions are observed with a significant laser-fluence window

(~30%) [reported at CLEO2003 as a news story; APL 85(7):1232, 2004, selected by the Virtual J.

Ultrafast Sci., September 2004, ROC patent I245321]. We also demonstrated dopant profile

engineering by near-infrared femtosecond laser activation [APL 88:1311104, March 27, 2006,

selected by Virtual J. of Nanoscale Sci. and Technology, Vol. 13, No. 14, April 10, 2006 and

Virtual Journal of Ultrafast Science, Vol. 5, No. 4, April 2006]. Preamorphizing implantation is not

required. We find dopant profiles in FLA-activated samples essentially duplicate those of

as-implanted ones even for junctions as deep as 100 nm below the surface. Laser-recrystallized

material was used successfully for fabricating thin film transitors [Opt. Exp., 15: 6981, 2007,

selected by Virtual J. of Ultrafast Sci., July 2007]. THz spectroscopic techniques were employed for

diagnostics of the fs-laser-annealed poly-Si material [Photonics Asia, invited talk, 2007, Opt. Exp.

Submitted, 2008]. It is shown that The transient mobilities of poly-Si with large (~ 500 nm) and

small (~ 50 nm) grain sizes, fitted by the Drude model, are 175.0±19.4 cm2/V s and 94.5±20.2

cm2/V s, respectively. We proposed that higher mobility in large-grain poly-Si by femtosecond

laser annealing is due to reduction of deep state density rather than tail state density.

18

6.

Tunable Lasers and Electro-Optic Devices for DWDM and Attosecond Generation with

Liquid Crystal (LC) Enabled Functionalities and other applications (Profs. Ci-Ling Pan,

Ru-Pin Pan, Andy H. Kung):

A digitally tunable laser diode, of which the output can be switched between wavelengths of

the ITU grid (100 GHz channel spacing) for DWDM optical communication systems (λ = 1550

nm), is demonstrated [Optics Express, 12 (26):6434, 2004; invited talk and paper at Photonics

West 2002; Taiwan Patent I223484, US patent filed]. Another design allows continuous,

mode-hop-free electronic tuning of the laser frequency over 20 GHz [Opt. Eng. 43(1):234, 2004;

OL 29(5):510, 2004]. Dynamic wavelength switching and selection were achieved with a liquid

crystal pixel mirror (LCPM). Fine tuning is achieved through an intra-cavity LC phase shifter.

As an application, we recently reported intra-cavity LC cell gap measurement [Opt. Exp.

13(20):1905, 2005]. This design concept has been extended to devices such as tunable optical

switches/ filters/ equalizers/ demultiplexers. Demultiplexing 16-channel 100-GHz -spaced signals

into a 62.5-μm multimode-fiber array was demonstrated. The central wavelength of each channel

was designed according to the 100-GHz ITU grid. Adjacent channel crosstalk is less than 30 dB.

The outputs of the channels are equalized to 65 dBm. The variation between different channels

reduced from 10 dB to less than 0.5 dB [IEEE Photon. Technol. Lett., 40(10):2254, 2004, ROC

patent disclosed, 2006]. This work was reported by Lightwave Europe in the November issue,

2004. Recently, we report automatic power equalization and stabilization with minimum ripple level

A specially designed SLM was developed and used in frequency synthesis of attosecond

pulses, in collaboration with Prof. Andy H. Kung [Phys. Rev. Lett. 100: 163906, 2008]. Using 7

Raman sidebands generated by molecular modulation in H2, we achievd the synthesis of periodic

waveforms consisting of a train of pulses that are 0.83 cycles long and have an electric field pulse

width of 0.44 fs.

The SLM composed of a row of five 14 mm high by 4 mm wide by 0.022 mm thick

liquid-crystal panels. The size and location of each panel is designed to match the sideband beam

size and to allow unimpeded passage of five sidebands. With this new modulator, a total of 7

sidebands can now be employed for waveform synthesis. The total bandwidth is 24931.2 cm

or 2

20

octaves.

We verify by optical correlation that the carrier-envelope phase is constant in these

waveforms when they are synthesized from commensurate sidebands. The estimated overall shift of

the carrier-envelope phase is less than 0.18 cycles from the first to the last pulse of nearly 10

pulses

in the pulse train.

7.

Generation of coherent mid- and far- infrared radiation in GaSe (Profs. Ci-Ling Pan and

Jung Y. Huang)

A table-top infrared light source with high intensity and wide tunability is constructed by use

of difference-frequency-mixing in GaSe nonlinear optical crystal. Tuning wavelengths from 2.4μm

to 28μm are obtained with highest energy output ~13μJ at 3.5μm. The output characteristics are

compared among pure and erbium doped crystals. Second-order nonlinear coefficient deff

of the

Er:GaSe crystals reveal a deff

of 55.3 pm/V, which is about 24% larger than that of pure GaSe. The

improvement of deff

can be attributed to the substitutive and interstitial doping of Er ion in GaSe

unit cell. [Opt. Exp. 14:5484, 2006, selected by Virtual J. of Ultrafast Sci., August 2006) and Virtual

J. of Biomed. Opt.]. We also report a study of the effect of optical absorption on generation of

coherent infrared radiation from mid-IR to THz region from GaSe crystal. The infrared-active

modes of ε-GaSe crystal at 236 cm

_{and 214 cm}

_{were found to be responsible for the observed}

optical dispersion and infrared absorption edge. Based upon phase matching characteristics of GaSe

for difference-frequency generation (DFG), new Sellmeier equations of GaSe were proposed. The

output THz power variation with wavelength can be properly explained with a decrease of

parametric gain and the spectral profile of absorption coefficient of GaSe. The adverse effect of

infrared absorption on (DFG) process can partially be compensated by doping GaSe crystal with

erbium ions. [Opt. Exp. 14:10636, 2006, selected by Virtual J. of Ultrafast Sci., January 2007, listed

in Virtual J. of THz Sci. and Technol., October 2006]. Recently, we proposed and demonstrated

coherent generation and spectral synthesis of terahertz radiation with multiple stages of optical

rectification [Opt. Exp., submitted, 2008]. This approach can potentially be useful for the generation

of single-cycle high-amplitude terahertz pulses, which is currently limited by the pulse walk-off

effect from group velocity mismatch.

8.

Nonlinear optical studies of Silicon nanocrystals and Nano-Silicon-based optoelectronics

(Profs. Jung Y. Huang, Ci-Ling Pan, and Dr. Jia-Min Shieh)

A novel material of Si nanocrystals embedded in a three-dimensional array of mesoporous

silica matrix has been studied by nonlinear optical techniques. We report sum-frequency generation

spectroscopic studies of Si-O polar nanostructures embedded in a three dimensional array of

mesoporous silica (MS) matrix by use of different frequency combinations with picosecond and

femtosecond configurations. Such unique electronic structure of Si nanocrystals (nc-Si) embedded

in SiO2 is opening up wide applications to flash memory and photonic devices. The effective

second-order nonlinear coefficient and Curie temperature of nc-Si are determined by surface sum

frequency generation spectroscopy. A resonance feature around 480 nm was observed. The effective

second-order nonlinear coefficient is estimated to be deff =3.7 pm/V. Nonlinearity is tentatively

attributed to Si-O nanostructures in this novel material. The effect of heating and cooling cycle on

SFG signals provides evidence of ferroelectricity for nc-Si embedded mesoporous silica. The Curie

temperature of the material is estimated to be 567K.

A two-terminal metal-oxide-semiconductor photodetector for which light is absorbed in the

nano-Si material described above as a capping layer on p-type silicon substrates was fabricated.

Operated at reverse bias, enhanced photoresponse from 300 to 700 nm was observed. The highest

optoelectronic conversion efficiency is as high as 200%. The enhancements were explained by a

transistorlike mechanism, in which the inversion layer acts as the emitter and trapped positive

charges in the mesoporous dielectric layer assist carrier injection from the inversion layer to the

contact, such that the primary photocurrent could be amplified [APL 90:

051105 2007, selected by

Virtural J. Nanoscale Sci. & Technol.2007]. This paper was at one time among the top 20 most

22

9.

Femtosecond Fiber Lasers and Applications (Profs. Gong-Ru Lin and Ci-Ling Pan)

9-1 Self-Steepening of Prechirped Amplified and Compressed 29-fs Fiber Laser Pulse in

Large-Mode-Area Erbium-Doped Fiber Amplifier

Prechirped amplification, soliton compression, and self-pulse-steepening of a 300-fs

stretch-pulse mode-locked erbium-doped fiber laser (EDFL) pulse in an ultrashort length

large-mode-area erbium-doped fiber amplifier (LMA-EDFA) and large-effect-area fiber (LEAF)

link are investigated. In situ amplified compression of the single-mode-fiber prechirped EDFL pulse

(broadened to 1.2 ps) is initiated in the LMA-EDFA at a pumping power of > 160 mW, which

provides a 20-fold pulsewidth compressing ratio for the incoming EDFL pulse and supports a

maximum output power of > 20 dBm. With an extremely short LEAF-based fifth-order soliton

stage, the amplified EDFL pulse can further be compressed down to a pulsewidth of 29 fs, which

gives rise to a total pulsewidth-compressing ratio of as high as 40. The LMA-EDFA-based

prechirped and amplified soliton compression leaves a small pedestal on the EDFL pulse with an

energy confinement ratio of 74%, providing a 20-dB magnified pulse energy of 2.3 nJ and a 10-dB

spectral linewidth of 150 nm. The self-steepening-induced blue-side spectral stretch by 1.3 THz is

elucidated.

Fig. 1. Experimental setup of an LMA-EDFA + LEAF amplified compressor link.

Fig. 2. Autocorrelation traces of the in situ amplified and compressed APM-EDFL pulses measured at different LMA-EDFA output powers.

9-2 Dynamic chirp control of all-optical format-converted pulsed data from a

multi-wavelength inverse-optical-comb injected semiconductor optical amplifier

By spectrally and temporally reshaping the gain-window of a traveling-wave semiconductor

optical amplifier (TWSOA) with a backward injected multi- or single-wavelength

inverse-optical-comb, we theoretically and experimentally investigate the dynamic frequency chirp

of the all-optical 10GBit/s Return-to-Zero (RZ) data-stream format-converted from the TWSOA

under strong cross-gain depletion scheme. The multi-wavelength inverse-optical-comb injection

effectively depletes the TWSOA gain spectrally and temporally, remaining a narrow gain-window

and a reduced spectral linewidth and provide a converted RZ data with a smaller peak-to-peak

frequency chirp of 6.7 GHz. Even at high inverse-optical-comb injection power and highly biased

current condition for improving the operational bit-rate, the chirp of the multi-wavelength-injection

converted RZ pulse is still 2.1-GHz smaller than

that obtained by using single-wavelength injection at a cost of slight pulsewidth broadening by 1 ps.

Fig. 3. Experimental setup. Amp.: amplifier.; ATT.: optical attenuator; DSO: digital sampling oscilloscope; EDFA: erbium doped fibre amplifier; OBPF: optical band-pass filter; OC: optical circulator; PC: polarization controller; PPG: PRBS pattern generator; TL: tunable laser. Electrical path: solid line. Optical path: dash line.

Fig. 4. BER performance of the back-to-back NRZ (blue circle) and the TWSOA converted RZ under DFBLD (black square) and FPLD (red diamond) based inverse-optical-comb injection.

9-3 All-Optical Decision-Gating of 10-Gb/s RZ Data in a Semiconductor Optical

Amplifier Temporally Gain-Shaped With Dark-Optical-Comb

We demonstrate a novel all-optical noninverted OC-192 return-to-zero (RZ) decision-gate

by using a semiconductor optical amplifier (SOA) which is gain-controlled to achieve an extremely

high cross-gain-modulation depth and a narrow gain window. A dark-optical-comb generated by

reshaping the optical clock RZ data in a Mach–Zehnder intensity modulator is employed as an

injecting source to temporally deplete most of the gain in the SOA. Such a dark-optical-comb

injected SOA decision-gate exhibits improved 3R regeneration performances such as a timing

tolerance of 33.5 ps, a Q-factor of 8.1, an input dynamical tolerance of 14 dB, and an extinction

ratio (ER) of 14 dB. The deviation between the wavelengths of backward injected

dark-optical-comb and input RZ data for optimizing the ER of the decision-gate is determined as Δλ

= 19 nm. Under a threshold operating dark-optical-comb power of 7 dBm, such a decision-gate can

recover the −18.5-dBm degraded RZ data with a bit-error-rate of less than 10−9 at 10 Gb/s. A

negative power penalty of −4.2 dB is demonstrated for the RZ data after 50-km propagation and

decision gating.

24

Fig. 5. Schematic diagram of the backward optical-comb injection SOA-based decision-gate.

Fig. 6. (Top) Distorted RZ data-stream with “11010” pattern at 10 Gb/s.(Bottom) Converted data stream.

9-4 Simultaneous pulse amplification and compression in all-fiber-integrated pre-chirped

large-mode-area Er-doped fiber amplifier

A large-mode-area Erbium-doped fiber amplifier (LMA-EDFA) based all-fiber-integrated

amplified compressor with ultrashort length of 5.37 m and ultralow pumping power (260 mW) is

proposed. The LMAEDFA suppresses nonlinear soliton-self-frequency-shift effect happened during

femtosecond pulse amplification, in which the fiber laser pulse is reshaped to a low-pedestal

hyperbolic-second shape with nearly 100% energy confinement. The pre-chirped amplification from

0.96 to 104 mW and the simultaneous compression of a passively mode-locked fiber laser pulse

from 300 to 56 fs is demonstrated. The input pulse energy of 24 pJ is amplified up to 2.6 nJ with

shortened pulsewidth of 56 fs and peak power as high as 46 kW.

Fig. 7. Autocorrelation traces (left) and corresponding pulse spectra (right) of the original, the pre-chirped and the amplified/compressed pulses.

9-5 Femtosecond mode-locked Erbium-doped fiber ring laser with intra-cavity loss

controlled full L-band wavelength tunability

By using a tunable-ratio optical coupler (TROC) to adjust the wavelength dependent

intra-cavity loss, a L-band mode-locked erbium-doped fiber-ring laser (ML-EDFL) is demonstrated

for generating wavelength-tunable femtosecond pulses. The change of output coupling ratio

introduces different intra-cavity loss and shifts the peak of mode-locked gain profile to provide

continuous detuning on wavelength of the ML-EDFL. A maximum tuning range of about 40 nm

(from 1565.1 to 1605.3 nm) by decreasing the output coupling ratio from 95% to 5% is obtained,

corresponding to a wavelength tuning slope of 2.25 nm/dB. The ML-EDFL exhibits a super-mode

suppressing ratio as high as 47 dB and a pulsewidth of <5 ps at repetition frequency of 1 GHz.

Nearly transform-limited pulsewidth of 580 fs is generated by linear dispersion compressing the

(b)

EDFL pulses with a 32.5m-long single-mode fiber under an output coupling ratio of 10%.

Fig. 8. Schematic diagram of the mode-locked EDFL with a TROC-based wavelength tuning configuration. Amp: microwave amplifier; COMB: electrical comb generator; MZM: Mach-Zehnder modulator; PC: polarization controller; RFS: radio-frequency synthesizer; TROC: tunable-ration optical coupler; WDM: wavelength division multiplexing coupler.

Fig. 9. The peak power and the pulsewidth of the pulses as the output coupling ratio adjust from 10% to 90%. Inset: The autocorrelation traces of the output pulses.

10. GaN-based Vertical Cavity Surface Emitting Laser and Light Emitting Diodes

（Prof. Hao-Chung Kuo and Tien-Chang Lu）

10-1. Study of high reflectivity mirror for blue high quality light emitter

In this part, we develop the high reflectivity epitaxially grown nitride mirror, usually in the

form of distributed Bragg reflector (DBR), using MOCVD epitaxy technique. The nitride material

system usually has a serious strain problem for the epitaxy of such multi-film structure. Therefore,

the fabrication of high reflectivity mirror for blue light emitter is a difficult topic. In this study, we

have developed a solution for the epitaxy of high-reflectivity reflector.

A crack-free GaN/AlN DBR incorporated with GaN/AlN superlattice (SL) layers was

successfully grown on a c-plane sapphire substrate (Figure 1(a)). We inserted three sets of

half-wave layers consisting of 5.5 periods of GaN/AlN SL layers and GaN layer in every five pairs

of the 20 pair GaN/AlN DBR structure to suppress the crack generation. The grown GaN/AlN

DBRs with SL insertion layers showed no observable cracks in the structure and achieved high peak

reflectivity of 97% at 399 nm with a stop band width of 14 nm(Figure 1(b)). Based on the x-ray

analysis (Figure 1(c)), the reduction in the in-plane tensile stress in the DBR structure with insertion

of SL layers could be responsible for the suppression of crack formation and achievement of high

reflectivity.

26 2700 2800 2900 3000 7800 7600 7200 7400 Qy // [ 0001 ] ( ×10 4 rl u) Qx // [10

1

Pumping energy (nJ/pulse)

Laser emission intensity versus pumping energy in semilogarithmic scale. The b vale estimated from the difference between the two dash lines is about 2x10-2. The inset shows the spectrum of the laser emission with a wavelength of 415.9 nm 400 410 420 430 440 450 0 50 100 150 200 250 300 350 P L in te n s ity (a .u .) Wavelength (nm) Bright area Dark area + A + B 5 　m

Micro-PL intensity mapping image of the VCSEL aperture.(b) Fine micro-PL scan inside the square area in (a). (c) PL spectra of bright (point A) and dark (point B) areas.

Figure 1 (a) The TEM image of GaN/AlN DBR; (b) The reflectivity spectrum of DBRs with and without superlattice; (c) the Reciprocal space maps of non-SL and SL samples.

10-2. Emission characteristics of optically pumped GaN-based vertical-cavity surface-emitting

lasers

The laser emission characteristics of a GaN-based vertical-cavity surface-emitting laser with

two dielectric distributed Bragg reflectors were investigated under optically pumped operation at

room temperature. The laser emitted wavelength at 415.9 nm with an emission linewidth of 0.25 nm

and threshold pumping energy of 270 nJ. The laser has a high characteristic temperature of about

278 K and high spontaneous emission coupling factor of 10−2. The laser emission showed single

and multiple spot emission patterns with spectral and spatial variations under different pumping

conditions.

(a)

_(b)

(c)

(d)

(c)

~3μm 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 0 2000 4000 6000 8000 10000 In te n s ity (a .u .)

Pumping energy (μJ/pulse)

440 445 450 455 460 0.0 0.2 0.4 0.6 0.8 1.0 1.2 0.17nm ~448nm In te nsit y ( a . u.) Wavelength (nm) 8 pairs Ta2O5/SiO2 25 pairs AlN/GaN Sapphire MQWs p-Ga N

(a)

(b)

(c)

(d)

Figure 2 (a) Schematic setup of pumping and μ-PL scanning. (b) Emission pattern of the VCSEL at pumping energy of 1.15 Eth with single laser emission spot and 1.12 Eth with two laser spots. The arrows indicate the position of the first and second emission spots. Emission spectrum at pumping energy of 1.15 Eth and 1.12 Eth, respectively. (c) PL spectra of bright (point A) and dark (point B) areas. (d) Laser emission intensity versus pumping energy in semilogarithmic scale. The b value estimated from the difference between the two dash lines is about 2x10-2. The inset shoes he spectrum of the laser emission with a wavelength of 415.9nm.

10-3. Study of characteristics of GaN vertical cavity surface emitting laser (VCSEL)

Following the success of laser action of GaN VCSEL using optical pumping, we further

investigated the characteristics and performance of GaN blue VCSEL. The structure of GaN

VCSEL is formed by a 3λ cavity sandwiched by a 25 pairs AlN/GaN distributed Bragg reflector

(DBR) and an eight pairs Ta2O5–SiO2 DBR (Figure 3(a)). The pumping condition could be

monitored by a CCD. The near field image was shown in figure 3(b) and laser occurred in the form

of spot emission at the center of pumping area. The GaN VCSEL emits a blue wavelength at 448

nm with a linewidth of 0.17 nm (Figure 3(c)) with a near-field emission spot diameter of about

3μm. The laser beam has a near linear polarization with a degree of polarization of about 84%. The

laser shows a high spontaneous emission coupling efficiency (β) of about 5×10-2 (Figure 3(d))

and a high characteristic temperature of about 244 K. The high beta value also implies the

thresholdless laser for the nitride material system is highly possible.

Figure 3 (a) The schematic diagram, (b) The near field image, (c) The threshold characteristics, and (d) The beta performance of of GaN VCSEL under optical pumping

10-1 100 101 10-2 10-1 100 101 102 103 No rm a liz ed inten s it y (a .u.)

Pumping energy(μJ/pulse)

28

10-4 Successfully fabricated low-temperature electrical pumping InGaN-MQW VCSELs by

hybrid mirrors

The GaN-based VCSEL structure was grown by MOCVD (EMCORE D-75). We use the

polished c-face (0001) 2-inch-diameter sapphire as a substrate for the epitaxial growth. The VCSEL

structure composed of a 5λ cavity, a 29 pairs AlN/GaN DBR as bottom mirror and an eight pairs

Ta2O5/SiO2 dielectric mirror as the top DBR reflector. By using lithograph technology, etching by

RIE and deposed contact metals on the substrate, we can successfully fabricate low-temperature

electrical pumping InGaN-MQW VCSELs by hybrid mirrors. The schematic diagram of the full

structure is shown in figure 4(a).

Figure 4(b) shows the photoluminescence emission intensity as a function of wavelength at

low temperature condition (77K). From the PL spectrum, we can find the center wavelength at

465nm and a distinct narrow linewidth of the peak nearluy 5.2Å which can be calculated the cavity

quality factor (Q) about 894. Figure 4(c) shows the variation of injection current with the voltage

and pumping energy.

Fig. 4(a). The schematic diagram of the electrical pumping VCSEL structure. (b) The PL spectrum of the structure has the center wavelength 465nm and a narrow linewidth 5.2A. (c) LIV curves of the VCSEL structure has lower turn-on voltages 3.4V.

10-5 Successfully achieved the Lasing Action of GaN-based Two Dimensional

Surface-emitting Photonic Crystal Laser

The nitride heterostructure in this experiment was grown by the metal-organic chemical vapor

deposition (MOCVD) system on sapphire substrate. The epitaxial structure consists of a 25 pairs

AlN/GaN DBR and a 5λ cavity. The 2D PCSEL was fabricated by following steps. First, 200 nm

Si3N4 film was deposited as a hard mask using PECVD and spun PMMA by spinner which was

n-contact ITO 10μm 8 pairs of Ta2O5/SiO2DBR p-contact passivation 5λ Cavity Sapphire 29 pairs AlN/GaN DBR MQW n-contact ITO 10μm 8 pairs of Ta2O5/SiO2DBR p-contact passivation 5λ Cavity Sapphire 29 pairs AlN/GaN DBR MQW 0.0 0.5 1.0 1.5 2.0 2.5 0 2 4 6 8 10 12 I-V L-I Current (mA) V ol tag e ( V ol t) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Inten sit y (arb.unit) 440 450 460 470 480 EL Intensit y ( a. u.) Wavelength (nm) 0.8I_th I th 1.3I_th 1.7I_th

(a)

(b)

(c)

patterned using an e-beam lithography. The lattice constants of PCs were in the range between 180

nm and 300 nm. The diameter of each device was 50 μm. Second, the sample was performed a dry

etching in an ICP-RIE system to etch GaN as deep as 400 nm. Finally, the sample was dipped in

BOE to remove the hard mask to complete 2D PCSEL. Figure 5(a) and (b) show the schematic

diagram of our 2D PCSEL, and the SEM image of fabricated 2D PCSEL in top view, respectively.

The threshold characteristics of PCSEL were also measured. Taking one of them for example (a

= 290 nm), the laser emission intensity from the PCSEL as a function of the exciting energy density

is shown in figure 5(c). The threshold energy density (Eth) was observed to be around 3.5 mJ/cm

.

The light intensity increased rapidly and linearly as the excitation energy density was above the

threshold. Figure 5(d) shows the lasing spectra at different pumping energy. A sharp and narrow

laser emission was then clearly observed as the pumping energy increased above the threshold

energy. The lasing wavelength located at 424.3 nm, and the FWHM of the laser is around 0.11 nm.

Other devices also could be observed the lasing actions occur at the similar threshold energy but

different lasing

wavelength.

Figure 5 (a) The schematic diagram of the overall photonic crystal surface emitting laser structure. (b) The SEM image of the full structure in top view. (c) The light output intensity as a function of the pumping energy density at room temperature. The threshold energy density was about 3.5 mJ/cm2_{. (d) The variation of the laser emission spectrum with}

increasing the pumping energy. The laser emission wavelength is 424.3nm with a linewidth of about 0.11nm

35 pairs AlN/GaN DBR stack N-GaN

P-GaN

Active layer

35 pairs AlN/GaN DBR stack N-GaN P-GaN Active layer 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 0.0 0.5 1.0 1.5 2.0 In ten s it y (a. u .) Energy density (mJ/cm2)

(a) (b)

(c)

(d)

30

10-6. High Light-Extraction GaN-based Vertical LEDs With Double Diffuse Surfaces

We have demonstrated the high light-extraction (external quantum efficiency ~40%) 465-nm

GaN-based vertical light-emitting diodes (LEDs) employing double diffuse surfaces. The high

scattering efficiency of double diffused surfaces could be responsible for the high light output

power. A schematic cross-section image of a GaN-based LED with double diffuse surfaces is shown

in Figure 6(a) and (b) shows the light output power (L-I curve) of sample A, sample B and

conventional LEDs. The sample B, the LED with double diffuse surfaces, and sample A, the LED

with flat omnidirectional reflectors, produced much higher light output as compared with that of

conventional LEDs under all our measurement condition. The calculated external quantum

efficiency of our proposal LEDs with double diffuse surfaces is about 40% at 20mA (λ~465 nm),

which could compete with structures of state of the art.

Figure 6 (c) and (d) shows the cross-sectional transmission electron microscope (TEM)

images of sample A and sample B, respectively. In Fig. 6(c), the top surface of p-type GaN was

quite flat, as can be seen in conventional LEDs; however, lots of hexagonal V-shape pits was

observed on p-type GaN surface of sample B, as shown in Fig. 6(d). Fig. 6(e) is an enlarged TEM

image of one hexagonal V-shape pit. As can be seen in this figure, the hexagonal V-shape pit

originated from threading dislocations and there is a thick dark band along the V-groove, being

indicative of thickness variation.

Figure 6 (a) Schematic cross section of a GaN-based LED with double diffuse surfaces. (b) Output power of sample A, sample B, and conventional LEDs measured by an integral-sphere as a function of a forward current. Cross-sectional transmission electron microscope (TEM) images of (c) flat p-GaN surface (sample A) and (d) hexagonal V-shape roughened p-GaN surface (sample B). (e) is an enlarged TEM image of one hexagonal V-shape pit.

10 -7. Fabrication and Characterization of GaN-based LEDs Grown on Chemical Wet-etched

Patterned Sapphire Substrates (CWE-PSS)

Characteristics of GaN-based LEDs grown on patterned sapphire substrate fabricated by the

chemical wet etching were specifically analyzed. By chemical wet etching, the sapphire substrate

exhibited a particular crystallography-etched facet of {1-102} R-plane with an inclined slope as

large as 57o, facilitating a significant enhancement of the light extraction efficiency. An

improvement of epitaxial quality was also achieved on CWE-PSS LEDs, according to device

reliability testing results.

Fig. 7(a) schematically depicts the GaN-based LED grown on the CWE-PSS and the

corresponding SEM micrograph of LED full structure is presented in Fig. 7(b). For fabricating the

CWE-PSS, the SiO2 film with hole-patterns of 3-μm-diameter and 3-μm-spacing was deposited

onto the sapphire substrate to serve as wet etching masks. The sapphire substrate was then wet

etched using an H3PO4-based solution at an etching temperature of 300 oC. Fig.7 (c) and (d) show

top and cross-section side views SEM images of the pattern sapphire substrate of etching time of

90s Fig.7 (e) and (f) show the evolution of CWE-PSS with the increase of sapphire etching time.

With the increasing of the etching time, the total area of C-plane will decrease due to its relative

faster etching rate than R-plane. Fig.7 (g) shows the measurement results of output power (L-I

curves) of CWE-PSS LEDs with different sapphire etching times. According to this figure, the

optimized CWE-PSS condition was achieved on the etching time of 90s, corresponding to an

enhanced factor of 1.4. Better reliability characteristics were also observed on the CWE-PSS LEDs,

as shown in Fig.7 (h).

Figure 7 (a) The schematic drawing of the device structure. (b) Cross- sectional side-view SEM images of the CWE-PSS LEDs Structure. (c)(d) The SEM images of the top and cross-section side views. (e)A top-view drawing depicts the evolution of the increasing etching time. (f)A schematic ray-tracing with increasing sapphire etching time.

(a)

(b) (c)

(h)

(d) (e)

(g)

32

(g) Output power measurement and CWE-PSS LEDs. (h) Reliability test of the conventional and CWE-PSS LEDs under stress condition of 55 and 50 mA.℃

10-8. Fabrication of InGaN/GaN MQW Nanorods LED by ICP-RIE and PEC Oxidation

Process with Self-Assembly Ni Metal Islands

We successful fabricated the InGaN/GaN MQW nanorods LED using Ni nano-masks,

ICP-RIE etching and PEC oxidation process. The PEC oxidation process can produces better

oxidation layer surrounding nanorod to isolate nanorods to electric pumping. A transparent contact

layer was deposited to form a connection with the exposed p-type of individual nanorod. We

estimate the mean dimension and density of the InGaN/GaN MQW nanorods LED as shown in Fig.

8(a) which shows the SEM images of InGaN/GaN MQW nanorods LED after ICP-RIE etching. The

SEM image of in Fig. 8(b) shows the Ni/Au contact metal deposited on InGaN/GaN MQW

nanorods LED after PEC oxidation process.

Fig. 8(c) shows the normalized PL intensity spectrum of the as-grown LED and nanorods

LED with/without PEC. An enhancement by a factor of 6/5 times in photoluminescence intensities

of nanorods with/without PEC process compared to that of as-grown structure. The peak

wavelength observed from PL measurement shows a blue shift of 3.8 nm of the nanorods without

PEC oxidation process and 8.6 nm of the nanorods with PEC oxidation process from that of the

as-grown LED sample. The blue shift maybe is attributed to strain relaxation in the well for

nanorods LED and intensity enhanced by scattering effect. The Fig. 8(d) shows the normalized EL

spectrum of the as-grown LED and nanorods LED samples with PEC process at an injection current

of 1mA. The EL spectrum shows 10.5 nm blue-shift of the nanorods with PEC from that of the

as-grown LED sample.

Figure 8 The SEM images of (a) InGaN/GaN MQW nanorods LED after ICP-RIE etching. (b) InGaN/ GaN MQW nanorods LED after deposited contact metal. (c) Normalized PL intensity spectra for as-grown LED and nanorods LED

(a)

(c)

(b)