二維準週期性光子晶體雷射之製程與特性分析

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(1)國立交通大學光電工程系顯示科技研究所碩. 士. 論. 文. 二維準週期性光子晶體雷射之製程與特性分析 Fabrication and Characteristics of Two-Dimensional Quasi-Periodic Photonic Crystal Lasers. 研究生：蔡豐懋指導教授：李柏璁. 教授. 中華民國九十五年六月.

(2) 二維準週期性光子晶體雷射之製程與特性分析. 研究生：蔡豐懋指導老師：李柏璁. 教授. 國立交通大學光電工程系顯示科技研究所碩士班. 摘要在本篇論文當中，我們使用三維平面波展開法以及二維有限時域差的方法去計算出對稱性光子晶體雷射結構的能帶圖、和共振場圖。這些有效的計算方法幫助我們能最佳化我們的光子晶體設計，並且把這些設計確實的應用在我們的製程當中。. 在製程的篇章中，主要分為兩大部分去介紹，分別是對稱性與非對稱性結構的製程。我們在對稱的薄膜結構上做了許多種不同設計的光子晶體元件去研究。而在非對稱性結構中，我們成功的把光子晶體寫在主動層與 DBR 接和的晶片上面。以上的製程步驟和遇到的困難以及解決方法都詳細的寫在內容中。. 最後，利用自行架設的 micro-PL 系統把我們製程出來的所有元件做量測與討論。從量測的結果與模擬的結果去討論，可以得知我們量測到的發光模態與我們預測的是相同的。並且，達到我們所預期的雷射特性、從設計去減少共振模態、準週期性結構在製程中對誤差的容忍度和 DBR 接和晶片發光的光子晶體雷射，這些結果都已從量測中得到。 ii.

(3) Fabrication and Characteristics of Two-Dimensional Quasi-Periodic Photonic Crystal Lasers Student：Feng-Mao Tsai Advisor：Prof. Po-Tsung Lee. National Chiao Tung University Department of Photonics & Display Institute. Abstract We calculated the band diagrams, photonic band gaps, resonance spectra, and resonance mode profiles of the symmetric and c two-dimensional photonic crystal lasers using 3D plane-wave-expansion method and 2D finite-difference time-domain method. These help us to optimize our photonic crystal design. And then, a modified quasi-periodic photonic crystal microcavity laser was designed.. In the fabrication, we introduced the procedures for two different structures. In the membrane structure, we demonstrated the basic photonic crystal lasers and the 12-fold quasi-periodic photonic crystal lasers. In the asymmetric structure, the wafer fusion technology was developed. And the PC microcavity structure was defined on the bonded sample successfully. All of the fabrication procedures for symmetric and asymmetric structure lasers were presented in detail.. The basic characteristics of two-dimensional quasi-periodic photonic crystal microcavity were measured by a micro-scale photoluminescence system. Furthermore, the characteristics were compared to the triangular lattice photonic crystal lasers. From the measurements, we achieve the goals of ultra-low threshold, high-Q, side mode reduction, the tolerance of QPC lasers, and PC devices lasing from DBR bonded wafer.. iii.

(4) Acknowledgements 首先我必須非常誠摯的感謝養育我並且在求學期間一路支持我的父母親，能讓我在這段路程中能過著衣食無缺的生活，使得我能專心於學業及其他各方面的發展。還有這段期間一直陪伴著我的女朋友小珮以及從北海道來的漂亮高貴喵，常常會在我遇到挫折與失落的時候給我最大的鼓勵，也會在成功的時候與我分享勝利的果實，非常感激她們對我的支持。碩士班這兩年，說不上是長還是短，但卻是人生當中讓我成長與改變最多的一個階段。在求學方面，從以往中制式的學習轉變成實際的操作，許多的問題都大部分要靠自己去發掘或解決。因此在一個團體群的合作與互助也比以往更顯得重要，而以下是要感謝這段時間當中幫助過我完成這篇文章的伙伴們。. 一開始要感謝我的指導教授李柏璁老師，謝謝老師在這兩年的蹲蹲教誨讓我受益良多，也協助我渡過許多困難。另外，有許許多多幫助過我的學長和同學們，讓我在實驗中遇到的困難能迎刃而解，在此都要非常感謝他們。特別是博士班學長盧贊文，提供給我了很多想法並且幫我解決許多疑惑。電子所黃世傑學長，指導我們許多製程上的困難。光電所的朱榮堂學長，提供我許多晶片融合的意見和製程材料。還有張吉東和魏士強學長一年來的帶領與教導。接下來不外乎是朝夕相處的實驗室同學們，范峻豪、陳鴻祺、陳思元、陳佳禾、蘇國輝、張資岳還有因製程而互相切磋學習的陳書志同學，謝謝他們的陪伴讓乏味的實驗室增添了許多色彩。還要感謝我的兩位電子所的大學同班同學，楊宗樺及吳居倫常常一起討論和互相協助。最後，也要謝謝最後這一年經常被我抓去做實驗的曾仲銓和游嘉銘，多虧了他們才能讓實驗迅速完成。還有，總是幫大家賣力跑腿買宵夜的江俊德學弟。. 還要感謝行政院國家科學委員會的計畫補助，在計畫編號 NSC-94-2752-E-009-007 下，使得我們有足夠的資源能進行所有的研究。再次感謝以上所有的人，豐富我在交大的兩年生活，並且協助我完成這份畢業論文。 2006/6/5 于新竹國立交通大學電資大樓 516 室. iv.

(5) Content Abstract (In Chinese)……………………………………………………………ii Abstract (In English)……………………………………………………………iii Acknowledgements……………………………………………………………..iv Content…………………………………………………………………………..v List of Tables…………………………………………………………………..viii List of Figures…………………………………………………………………..ix. Chapter 1. Introduction. 1.1.. Photonic Crystals…………………………………………………………1. 1.2.. Photonic Crystals Lasers………………………………………………….5. 1.3.. Quasi-Periodic Photonic Crystal Lasers………………………………….8. 1.4.. An Overview of This Thesis…………………………………………….11. Chapter 2. Device Structures. 2.1.. Introduction……………………………………………………………...12. 2.2.. Devices Structures……………………………………………………….13 2.2.1. Membrane Structures……………………………………………..14 2.2.2. Wafer Bonding Structures………………………………………...14. 2.3.. Quasi-Periodic Photonic Crystal Lasers…………………………………17 2.3.1. Basic Theory of Quasi-Periodic Photonic Crystal Lasers………...17 2.3.2. 12-fold Quasi-Periodic Photonic Crystal Lasers………………….18 2.3.3. Finite-Different Time-Domain Method…………………………..21 2.3.4. Band Structure and Mode Analysis……………………………....25. 2.4.. Conclusion……………………………………………………………….27. v.

(6) Chapter 3. Fabrication of Membrane Structure Photonic Crystal Lasers. 3.1.. Introduction……………………………………………………………...28. 3.2.. Fabrication of Two-Dimensional Photonic Crystal Lasers……………...28 3.2.1. Dielectric Deposition……………………………………………..29 3.2.2. Photonic Crystal Patterns Definition……………………………..29 3.2.3. Patterns Transfer………………………………………………….33 3.2.4. Substrate Undercut………………………………………………..38. 3.3.. Fabrication Results ……………………………………………………...41 3.3.1. Triangular Periodic Photonic Crystal Lasers……………………..41 3.3.2. Quasi-Periodic Photonic Crystal Lasers………………………….41 3.3.3. Modified Quasi-Periodic Photonic Crystal Lasers……………….43. 3.4.. Conclusion………………………………………………………………44. Chapter 4. Fabrication of Wafer Bonding Structure Photonic Crystal Lasers. 4.1.. Introduction……………………………………………………………...46. 4.2.. Fabrication of Photonic Crystal Lasers with DBR Bonding…………….46 4.2.1. Preparation for Wafer Bonding…………………………………...47 4.2.2. Wafer Bonding System…………………………………………...49 4.2.3. Substrate Removal………………………………………………..51 4.2.4. Photonic Crystal Patterns Definition and Transfer……………….52. 4.3.. Fabrication Results & Conclusion………………………………………54. vi.

(7) Chapter 5. Measurement Results. 5.1.. Introduction……………………………………………………………...57. 5.2.. Basic Lasing Characteristics…………………………………………….59 5.2.1. Measurement Results from Membrane Structures………………..59 5.2.2. Measurement Results from DBR-Bonding Structures……………70. 5.3.. Conclusion……………………………………………………………….74. Chapter 6. Conclusion……………………………………………….75. References………………………………………………………………….77 Vita……………………………………………………………………………79. vii.

(8) List of Tables Table 2.1 The thermal conductivities and refractive indices with different materials……...15 Table 4.1 The thermal expansion coefficients of stainless steel and molybdenum material with different temperatures……………………………………………………...50 Table 5.1 Table shows the devices lasing rate with random varying lattice constant in statistic over 300 samples……………………………………………………….70 Table 5.2 The table shows the threshold with random varying of lattice constant in 12-fold QPC lasers……………………………………………………………………….70. viii.

(9) List of Figures Fig. 1.1. The schematic illustration of one-, two-, and three-dimensional photonic crystals. Different dielectric constants were represented in the different colors……………1. Fig. 1.2. A typical reflectance spectra for the AlGaPSb/InP at 1550nm DBR. The schematic at right side is a simple structure of DBR………………………………………….2. Fig. 1.3. A typical TE mode 2-D photonic crystals band structure calculated by 2-D plane-wave expansion (PWE) method. The shadow region is the PBG of this 2-D photonic crystals with r/a = 0.3, a = 500 nm………………………………………4. Fig. 1.4. The illustrations show 2-D PCs with (a) a point defect by removing one air hole. (b) a line defect by removing one row of air holes……………………………….. 4. Fig. 1.5. Gap map for a (a) square (b) triangular lattice of air columns with dielectric medium, ε = 11.4 . PBGs in a triangular lattice are usually broader than a square one, in the same r/a ratio. The yellow region in (b) is called a complete band gap which included the photonic band gaps with TM mode and TE mode…………….6. Fig. 1.6. A scheme of cross section of the photonic crystal microcavity. The combination of distributed Bragg reflection from 2-D photonic crystal and TIR from the air cladding constructed a quasi-3D light confinement mode…………………………7. Fig. 1.7. Schematic figures showing the (a) octagonal (b) decagonal (c) dodecagonal quasi-periodic photonic crystal patterns……………………………………………8. Fig. 1.8. Schematics of a microgear laser and resonant modes. (a) The H z standing wave of WGM matched with the grating number in this microgear laser. (b) The possible 2. resonance modes of H z …………………………………………………………9 Fig. 2.1. (a) Schematics of our designed epitaxial QWs structure. (b) A typical PL spectrum of our MQWs. It is centered at 1550 nm with 200nm span………………………..13. Fig. 2.2. A side view of the membrane structure. The light will be confined in membrane structure by perfect mirrors for the x direction, and by the air clad based on TIR for the z direction………………………………………………………………………14. Fig. 2.3. The illustrations of 2-D photonic crystal asymmetric structure bonding with (a) sapphire substrate (b) DBR substrate in side view………………………………...15. Fig. 2.4. The calculated reflectivity of DBR which can be up to 99.5% in the wavelength from 1450 to 1600 nm……………………………………………………………...16. Fig. 2.5. A dodecagonal QPCs in reciprocal lattice space…………………………………..17. ix.

(10) Fig. 2.6. (a) The scheme shows a dodecagonal structure in basic reciprocal space. (b) The circle represents a unit cell of a dodecagonal QPCs……………………………….19. Fig. 2.7. The illustration of dodecagonal QPCs with (a) 1 (b) 7 (c) 19 air holes. D1 represent the meaning of 1 missing air hole and D2 represent 7, D3 represent 19 missing air holes, etc……………………………………………………………………………20. Fig. 2.8 Fig. 2.9 Fig. 2.10. The scheme illustrate the design of the 12-fold modified QPC microcavity laser...20 JK JJK Temporal division of E and H components……………………………………..23 Transmission spectra of 12-fold QPCs from r/a = 0.36 to 0.42. The inserts show the simulation structure and illustrates the position of source and detector……...25. Fig. 2.11. The illustration shows the normalized frequency of calculated lasing modes with the different normalized hole radius. The mode profiles on the right correspond to their symbols in the scheme on the left. The hollow symbols with solid lines show the different kinds of WGMs……………………………………………………..26. Fig. 3.1. A illustration of epitaxial structure of InGaAsP QWs for membrane PC lasers. The thickness of active region is about 220 nm………………………………………...28. Fig. 3.2. The illustrations are the same CAD pattern of triangular lattice PC microcavity laser with different electron beam dosage (a) 1.2 fC (b)1.4 fC (c)1.6 fC (d)1.8 fC (e)2.1 fC. Obviously, the PCs holes in larger dosage are more circular than that in smaller one. There were still some residues of PMMA inside the air holes in (a) (b) because of the insufficient for electron dosage……………………………………………...31. Fig. 3.3. SEM top view of PC patterns after the PMMA development process. In the development process, the unusual control in temperature will cause (a) the creased PMMA surface and (b) distorted circle at the edge of PCs………………………..33. Fig. 3.4. (a) A side view SEM picture of PC patterns transferred to MQWs by ICP/RIE dry etching processes. (b) The higher magnification of (a) from a window…………...35. Fig. 3.5. (a) A top view picture of PC patterns from high magnification OM system. (b) The higher magnification from (a)……………………………………………………...35. Fig. 3.6. The dry etching profiles fabricated with the recipe of (a) 73W, 0.3mTorr (b) 73W, 0.4mTorr (c) 85W, 0.3mTorr (d) 85W, 0.4mTorr in RF power and the flowing pressure of Cl2 gas, respectively…………………………………………………...37. Fig. 3.7. A side view of PCs with modified etching recipes in ICP/RIE dry etching process……………………………………………………………………………...38. x.

(11) Fig. 3.8. The illustration of (a) a 40° etching stop plane in (0, 1, -1) direction (b) a 95° etching stop plane in (0, -1, -1) direction of InP materials………………………...39. Fig. 3.9. (a) The top view of a array of PC lasers. The lower PC lasers of the array have larger radius of air hole. (b) Small wedges under every hole have no chance to meet each other at the corners of the etched feature because the smaller radius of air holes………………………………………………………………………………..39. Fig. 3.10. (a) The SEM of the aligning step before electron-beam writing. (b) A top view of an array of 2D PC lasers in modified undercut procedure………………………..40. Fig. 3.11. The top view of two-dimensional photonic crystal membrane lasers array. This microcavity is formed by 7 missing air holes…………………………………….41. Fig. 3.12. (a) The oblique view of fabricated QPC microcavity lasers suspended membrane structure. (b) The top view of 12-fold QPC membrane lasers array with D2 (left) and D3 (right) microcavity. (c) The top view of 8-fold QPC membrane lasers array with D2 microcavity. (d) The top view of circular PCs membrane lasers array with D2 microcavity……………………………………………………………………42. Fig. 3.13. (a) A top view of 12-fold modified QPC membrane lasers array with D2 microcavities. (b) The higher magnification of one modified QPC laser from (a).43. Fig. 3.14. An overview of fabrication processes of two-dimensional photonic crystal membrane structure lasers………………………………………………………...45. Fig. 4.1. A illustration of epitaxial structure of InGaAsP QWs for wafer bonding structure lasers. InGaAs etching stop layer is used to protect the MQWs during the removing InP substrate process……………………………………………………………….47. Fig. 4.2. A top view of two bonding structure samples after channel patterns defined……..48. Fig. 4.3. The scheme of top view and the side view of wafer bonding fixture. A stuck wafer was clipped on the wafer bonding fixture………………………………………….49. Fig. 4.4. A illustration of the wafer bonding (fusion) system……………………………….50. Fig. 4.5. The picture shows a tilt sample after wafer bonding process. The upper layer of sample is a InP/InGaAsP QWs wafer and the lower one is a DBR wafer…………51. Fig. 4.6. The picture shows a tilt sample after remove InP substrate. The smooth and glossy surface is the InGaAsP MQWs with DBR substrate……………………………….52. Fig. 4.7. The SEM top view of the (a) D2 (b) D3 PC lasers bonding with DBR wafer…….54. Fig. 4.8. An overview of fabrication processes of two-dimensional photonic crystal with DBR or Sapphire wafer bonding…………………………………………………...56. xi.

(12) Fig. 5.1. (a) The picture shows our micro-PL system. (b) The scheme illustrates the configuration of (a)………………………………………………………………...57. Fig. 5.2. A typical lasing spectra above threshold of a two-dimensional D2 microcavity QPC laser. The FWHM of this lasing mode is 0.15 nm at 2.86 mW pump power and the inset indicated near-threshold lasing spectrum at 0.155 mW……………………...60. Fig. 5.3. A typical lasing spectra above threshold of a two-dimensional D3 microcavity QPC laser. The FWHM of this lasing mode is 0.18 nm at 3.26 mW pump power and the inset indicated near-threshold lasing spectrum at 0.312 mW……………………...61. Fig. 5.4. The illustration of the lasing spectra of one QPC laser at the (a) below threshold (b) near threshold (c) above threshold (d) 20 times threshold pump power…………..62. Fig. 5.5. The L-L curve of two-dimensional QPC lasers with D2 and D3 microcavity. The thresholds are estimated to be 0.186 and 0.246 mW input pump power, respectively………………………………………………………………………...63. Fig. 5.6. The L-L curve of two-dimensional triangular lattice PC laser with D2 microcavity. The threshold is estimated to be 0.6 mW input pump power……………………...63. Fig. 5.7. Lasing wavelength tuning caused by varying lattice constants. The inserts illustrate its corresponding lasing mode……………………………………………………..64. Fig. 5.8. The defect modes in normalized frequency of modified 12-fold D2 QPC microcavities. The individual solid circles denote the measured data……………..65. Fig. 5.9. Lasing mode polarization of (a) 12-fold QPC lasers (b) triangular lattice PC laser………………………………………………………………………………...66. Fig. 5.10. (a) The well-confined WGM profile in magnetic field with azimuthal number six of the microcavity without and (b) with a central air-hole……………………….66. Fig. 5.11. The side mode is greatly reduced by inserting the central air hole. The upper and lower lasing spectrum is a 12-fold QPC microcavity without and with a central air hole, respectively…………………………………………………………………67. Fig. 5.12. The illustration shows the inner-most layer (R1) and the outer layer (R3) air-holes in D2 QPC microcavity laser.…………………………………………………….68. Fig. 5.13 The scheme shows the lasing spectrum with the random varying of lattice constant. (a) Vary the inner-most air-holes in D2 QPC microcavity laser from 0% to 7% lattice constant position. (b) Vary the 2nd, 3rd and 4th layer air hole in D2 QPC microcavity laser from 0% to 7% lattice constant position. Nevertheless, the inner-most air-holes were fixed on the proper position of lattice constant………69. xii.

(13) Fig. 5.14. The illustrations show the two different DBR-bonded wafer. The numbers represent the measurement position of a wafer from the center (number 2) to the edge……………………………………………………………………………….71. Fig. 5.15. The comparison of two different bonded wafer. The enhancement of two wafers is 3 and 9 times, respectively………………………………………………………..72. Fig. 5.16. (a) The resonance mode spectrum (b) The lasing mode spectrum and L-L curve (the insert) of triangular lattice D2 PC lasers with bonded DBR substrate………73. xiii.

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