Effects of Built-In Polarization and Carrier
Overflow on InGaN Quantum-Well Lasers
With Electronic Blocking Layers
Jun-Rong Chen, Chung-Hsien Lee, Tsung-Shine Ko, Yi-An Chang, Tien-Chang Lu, Member, IEEE,
Hao-Chung Kuo, Senior Member, IEEE, Yen-Kuang Kuo, and Shing-Chung Wang, Life Member, IEEE, Fellow, OSA
Abstract—Effects of built-in polarization and carrier over-flow on InGaN quantum-well lasers with a ternary AlGaN or a quaternary AlInGaN electronic blocking layer (EBL) have been numerically investigated by employing an advanced de-vice-simulation program. The simulation results indicate that the characteristics of InGaN quantum-well lasers can be improved by using the quaternary AlInGaN EBL. When the aluminum and indium compositions in the AlInGaN EBL are appropriately designed, the built-in charge density at the interface between the InGaN barrier and the AlInGaN EBL can be reduced. Under this circumstance, the electron leakage current and the laser threshold current can obviously be decreased as compared with the laser structure with a conventional AlGaN EBL when the built-in polarization is taken into account in the calculation. Furthermore, the AlInGaN EBL also gives a higher refractive index than the AlGaN EBL, which is a benefit for a higher quantum-well optical confinement factor in laser operations.
Index Terms—AlInGaN, electronic blocking layer (EBL), InGaN, numerical simulation, semiconductor lasers.
I. INTRODUCTION
G
AN-BASED semiconductor lasers and light-emitting diodes have become the most promising light sources in the applications of high-density optical storage systems and solid-state lighting [1], [2]. Although these optoelectronic devices have already been commercialized, superior operation performance and shorter emission wavelength are expected as challenges for the next-generation devices. Regarding the GaN-based semiconductor lasers, there have been lots of re-search groups recently devoted to realizing high-power and short-wavelength laser diodes. Kink-free blue-violet laser diodes of 100 mW were demonstrated by Asano et al. in 2003 [3]. Ultraviolet laser diodes with 350.9-nm-lasing wavelength were also realized by Kamiyama et al. in 2005 [4]. Furthermore,Manuscript received July 4, 2007; revised August 13, 2007. This work was supported in part by the MOE ATU program and in part by the National Science Council of the Republic of China under Contracts NSC 95-2120-M-009-008, NSC 95-2752-E-009-007-PAE, NSC 95-2221-E-009-282, and NSC 95-2112-M-018-007.
J.-R. Chen, T.-S. Ko, Y.-A. Chang, T.-C. Lu, H.-C. Kuo, and S.-C. Wang are with the Department of Photonics and Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu 30050, Taiwan, R.O.C. (e-mail: [email protected]; [email protected]; [email protected]; [email protected]; hckuo@ faculty.nctu.edu.tw; [email protected]).
C.-H. Lee and Y.-K. Kuo are with the Department of Physics, National Changhua University of Education, Changhua 50058, Taiwan, R.O.C. (e-mail: [email protected]; [email protected]).
Digital Object Identifier 10.1109/JLT.2007.909908
single-mode blue-violet laser diodes with low beam divergence and high catastrophic optical damage level were demonstrated by Ryu et al. in 2006 [5]. These breakthroughs make GaN-based laser diodes the potential light sources in the applications of extra-large-capacity optical storage system, biological sensing, and optical catalyst. However, the inherent problem of piezo-electric and spontaneous polarizations in -plane GaN-based alloys is one of the most important properties which limit the development of GaN-based optoelectronic devices. The built-in polarization causes a strong deformation of the quantum wells accompanied by a strong electrostatic field. Under these cir-cumstances, electrons and holes are separated in the quantum wells, leading to a reduction of the photon emission rate and the internal quantum efficiency [6]. Furthermore, Piprek et al. found that the polarization of the AlGaN electronic blocking layer (EBL) has a strong effect on the laser threshold current due to the large polarization charges [7].
Several methods have been provided to eliminate or reduce the polarization effects, such as heavy silicon (Si) doping in quantum barriers [8], nonpolar ( - and -planes) quantum wells grown on -plane sapphire and -LiAlO [9], [10], and semipolar quantum wells grown on -plane sapphire [11], [12]. Nevertheless, heavy Si doping in quantum barriers may induce free-carrier absorption, which results in the increase of laser threshold current. As for the nonpolar and semipolar InGaN/GaN quantum wells, high dislocation density caused by large lattice mismatch and stacking faults inhibits the related development [13]–[15].
Recently, an approach to control the electrostatic fields by using quaternary AlInGaN layers reported by Khan et al. could be an attractive alternative for -plane GaN-based heterostruc-tures since the introduction of quaternary AlInGaN layers would allow us to control both spontaneous and piezoelectric polar-izations by choosing different aluminum and indium composi-tions [16], [17]. Since the built-in electric fields have a great impact on the properties of GaN-based laser diodes, we sys-tematically investigate the effects of polarization on threshold current and carrier overflow using the LASer Technology Inte-grated Program (LASTIP) simulation program [18]. By appro-priately designing the aluminum and indium compositions in AlInGaN EBLs, the built-in charge density at the interface be-tween InGaN barrier and AlInGaN EBL can be compensated. Under this circumstance, the AlInGaN EBL can effectively in-hibit the electron overflow than the conventional AlGaN EBL, and thus, the performance of the InGaN quantum-well lasers can be enhanced.
TABLE I
LAYERSTRUCTURE ANDROOM-TEMPERATUREPHYSICALPARAMETERS OF THEINGAN QUANTUM-WELLLASERUNDERSTUDY (d —LAYERTHICKNESS;N —DOPEDCARRIERDENSITY;n—REFRACTIVEINDEX ATWAVELENGTH400 nm;— THERMALCONDUCTIVITY).
THEDOPEDCARRIERDENSITYN REPRESENTS THEACTUALDENSITY OFFREECARRIERS
II. THEORETICALMODEL ANDDEVICESTRUCTURE
In order to achieve high-performance GaN-based laser diodes, systematic and compact theoretical modeling is a necessary approach to improve the existing laser structures and to understand the internal physical processes, which provides the timely and efficient guidance toward the optimal structure design and device parameters. By performing computational simulations, we can expect the trend of device design and un-derstand the main physical factor which limits the performance of GaN-based laser diodes.
The self-consistent LASTIP simulation program combines band structure and gain calculations with 2-D simulations of wave guiding, carrier transport, and heat flux. The carrier-trans-port model includes drift and diffusion of electrons and holes in devices. The built-in polarization induced by spontaneous and piezoelectric polarizations is considered at heterointerfaces of nitride-related devices. In the quantum wells, self-consistent Poisson and Schrödinger equations were recomputed at every bias point for the states of quantum-well levels and carrier dis-tributions. The physical model of the strained InGaN quantum wells is considered in such a way that the conduction bands are assumed to be parabolic, and the valence-band structures, which include the coupling of the heavy-hole, the light-hole, and the spin-orbit split-off bands, are calculated by the 6 6 Hamiltonian with an envelop function approximation [19], [20]. Free-carrier gain model, including a Lorentzian broad-ening function with a 0.1-ps scattering time [21]–[23], is used in calculating the optical gain of the quantum wells. The calcu-lations of carrier capture and escape from the quantum wells are considered in accordance with the model provided by Romero et
al. [24]. More descriptions about the physical models utilized in
the LASTIP simulation program can be found in [25] and [26]. In this simulation, we first assume that the InGaN laser diode is grown on an n-type GaN layer that is 3.0 m in thickness. On top of this GaN layer are a 0.1- m-thick n-type In Ga N compliant layer and a 1.0- m-thick n-type Al Ga N
cladding layer, followed by a 0.1- m-thick n-type GaN guiding layer. The multiple-quantum-well active region consists of two 2-nm-thick In Ga N quantum wells and 5-nm-thick In Ga N barriers. A 20-nm-thick p-type Al Ga N or p-type AlInGaN EBL is grown on top of the active region to reduce an electron leakage into the p-type GaN layer [27], [28]. Furthermore, a 0.1- m-thick p-type GaN guiding layer and a 1.0- m-thick p-type Al Ga N cladding layer are grown. Finally, a 0.1- m-thick p-type GaN cap layer is grown to complete the structure. The effective active region of the ridge geometry is 2 m in width and 500 m in length. The reflectivities of the two end mirrors are set at 20% and 50%, respectively. The doping concentrations in each layer and the detailed device structure are described in Table I.
III. MATERIALPARAMETERS
Proper material parameters are essential to obtain correct sim-ulation results. The material parameters of the binary semicon-ductors required for calculations are taken from the paper by Vurgaftman and Meyer [29] and summarized in Table II. As for AlInGaN materials, a linear interpolation between the parame-ters of the relevant binary semiconductors is utilized except for the bandgap energies. For physical parameter , the interpola-tion formula is [30]
Al In Ga N
AlN InN GaN (1)
The AlInGaN bandgap energies can be expressed as a weighted sum of the bandgap energies of relevant ternary semiconductors with appropriate bandgap-bowing parameters. Specifically, the AlInGaN bandgap energies are calculated by the following ex-pressions [31]:
AlInGaN
AlInN InGaN AlGaN
TABLE II
MATERIALPARAMETERS OF THEBINARYSEMICONDUCTORSGaN, AlN,ANDInNATROOMTEMPERATURE.(1 = 1 ; 1 = 31 = 31 )
AlInN
InN AlN AlInN (3)
InGaN
GaN InN InGaN (4)
AlGaN
GaN AlN AlGaN (5)
(6)
where , , and represent the compositions
of aluminum, indium, and gallium in the AlInGaN material system, respectively. The bandgap-bowing parameters of AlInN, InGaN, and AlGaN are 2.5, 1.4, and 0.7 eV, respectively [29].
The built-in polarization induced due to spontaneous and piezoelectric polarizations is known to influence the perfor-mance of nitride devices. In order to consider the built-in polarization within the interfaces of nitride devices, the method developed by Fiorentini et al. is employed to estimate the built-in polarization, which is represented by fixed interface charges at each heterointerface. They provide explicit rules to calculate the nonlinear polarization for nitride alloys of arbitrary composition [32]. Specifically, the spontaneous polar-ization of ternary nitride alloys can be expressed by
Al Ga N (7) In Ga N (8) Al In N (9) The spontaneous polarization of the quaternary AlInGaN can be calculated in a similar way as that shown in (2). As for the piezoelectric polarization of AlInGaN, InGaN, and AlGaN, it can be calculated by the following expression:
Al In Ga N
AlN InN GaN (10)
where AlN for (11) AlN for (12) GaN (13) InN (14) (15) where and are the lattice constants of the substrate and epitaxial layer, respectively. The total built-in polarization is the sum of spontaneous and piezoelectric polarizations. At an abrupt interface of a top/bottom layer heterostructure such as InGaN/GaN or AlGaN/GaN, the polarization can decrease or increase within a bilayer, causing a fixed polarization charge density defined by [33]
bottom top
bottom bottom top top
TABLE III
NETSURFACECHARGEDENSITY ATEACHINTERFACE OF THEInGaN LASERDIODE
For the InGaN quantum-well lasers under study, the net surface charges at all interfaces are calculated and listed in Table III . Al-though the interface charges can be obtained by this theoretical model, experimental investigations often find a weaker built-in polarization than that predicted by theoretical calculation. It is mainly attributed to partial compensation of the built-in polar-ization by defect and interface charges [34]. Typical reported experimental values are 20%, 50%, or 80% smaller than the theoretically calculated values [35]–[37]. As a result, 0% to 40% of the theoretical polarization values are used in our sim-ulation to study the effects of built-in polarization on the laser performance.
The thermal conductivities of nitride compounds listed in Table I are obtained from the values of binary GaN, AlN, and InN by considering the impact of alloy and the interface scat-tering of phonons. In our simulation, the thermal conductivities of GaN, AlN, and InN are 1.3, 2.85, and 0.45 W/cm K, re-spectively [25]. As for the parameter of refractive index, Adachi model is employed to calculate the refractive-index values in each layer listed in Table I as well [38]. Band offset ratio, which is defined as the ratio between the conduction-band offset and the valence-band offset of the InGaN/InGaN quantum well, is assumed to be 0.7/0.3 based on the published works [39], [40].
IV. SIMULATIONRESULTS ANDDISCUSSION
The energy band diagram of the InGaN/InGaN double quantum-well active region with a conventional Al Ga N EBL at 500-mA injection current is shown in Fig. 1. Since the threshold current of the InGaN quantum-well laser with an Al Ga N EBL is larger than 300 mA when the 40% polarization is considered in the calculation, we choose the injection current at 500 mA in order to analyze the internal physical processes of this laser diode above threshold and at higher operation current. In Fig. 1, the dashed line is calculated without considering the interface charge density, and the solid line is calculated with 40% interface charge density listed in Table III. It can be found that the conduction and valence bands are strongly deformed when the built-in polarization is assumed to be 40% of the theoretically calculated values. Although the injection current is 500 mA, the built-in polarization field still
Fig. 1. Energy band diagram of the InGaN/InGaN double quantum-well active region at 500-mA injection current. (a) Conduction bands for 0% (dashed line) and 40% (solid line) polarizations. (b) Valence bands for 0% (dashed line) and 40% (solid line) polarizations.
significantly deforms the energy band diagram in this operation current [18]. It is noteworthy that the energy barrier height created by Al Ga N EBL is substantially reduced by the high density of positive polarization charges at the interface between the InGaN barrier layer and the AlGaN EBL. Under this condition, the electrons are attracted by a Coulomb force and accumulate at this interface, which leads to a strong band bending. Consequently, the increase of laser threshold current will be expected due to the enhanced electron carrier leakage from the active layer to the p-type cladding layer. The leakage current results in an increased nonradiative recombination and lowers the internal quantum efficiency particularly for laser diodes operated at high injection level or at high operation temperature. The vertical profiles of electron-concentration distribution and conduction-band edge in the active region at 500-mA injection current are shown in Fig. 2 for laser structure with Al Ga N EBLs. We also compare different polariza-tion percentage values, i.e., without polarizapolariza-tion [Fig. 2(a)] and with 40% polarization [Fig. 2(b)]. It is obviously observed that a large number of electrons are attracted by the positive polar-ization charges and accumulate at the AlGaN EBL in the case of 40% polarization [Fig. 2(b)]. This condition makes a strong band bending at the InGaN/AlGaN interface, which lowers the AlGaN energy barrier relative to the electron quasi-Fermi level from 180 to 90 meV when the polarization percentage value changes from 0% to 40%. Although the energy barrier can be higher by increasing the p-type doping concentration in the AlGaN EBL, it is difficult to achieve a high p-type conductivity
Fig. 2. Vertical profiles of electron-concentration distribution and conduction-band edge in the active region of the laser structure with AlGaN EBL at 500-mA injection current. (a) 0% polarization. (b) 40% polarization.
in the p-type AlGaN alloys due to the high activation energy of Mg dopants [41].
In order to reduce the high density of interface charges at the InGaN/AlGaN interface, the quaternary AlInGaN EBL could be used to replace the conventional ternary Al Ga N EBL. Since it is assumed that the laser structures are grown on GaN bulk, the strains of AlGaN and InGaN epitaxial layers are ten-sile and compressive, respectively, which makes the directions of the piezoelectric polarization of AlGaN and InGaN opposite. Therefore, by employing appropriate aluminum and indium compositions in the AlInGaN EBL, it was found that the built-in charge density at the interface between the In Ga N barrier and AlInGaN EBL can be compensated according to the results of theoretical calculation. The aluminum and indium compositions are determined by fixing a specific aluminum composition and varying the indium composition to find the minimum interface charge density. When different aluminum compositions are chosen, there are corresponding indium com-positions which make the InGaN/AlInGaN interface charge density minimum. Therefore, several different aluminum and indium compositions can reach this requirement. For com-parison purpose, Al In Ga N is chosen to be the quaternary EBL in this paper because its energy bandgap is nearly identical to that of the original Al Ga N EBL after considering the strain-induced bandgap variation in both EBLs. The interface charge density between the In Ga N
bar-rier and the Al In Ga N EBL is cm ,
which is calculated by (7) –(14). This value is dramatically reduced as compared with that of the conventional Al Ga N EBL.
Fig. 3 shows the vertical profiles of the electron-concentra-tion distribuelectron-concentra-tion and conducelectron-concentra-tion-band edge without polariza-tion [Fig. 3(a)] and with 40% polarizapolariza-tion [Fig. 3(b)] in the
ac-Fig. 3. Vertical profiles of electron-concentration distribution and conduction-band edge in the active region of the laser structure with AlInGaN EBL at 500-mA injection current. (a) 0% polarization. (b) 40% polarization.
tive region at 500-mA injection current for laser structure with AlInGaN EBLs. The electron-concentration distributions and conduction-band diagrams of the laser structures with AlGaN and AlInGaN EBLs are nearly identical when the built-in polar-ization is not taken into account [Figs. 2(a) and 3(a)]. Therefore, we expect that the laser performance will be similar, which is shown in later simulation results. On the contrary, in the case of considering the 40% built-in polarization, the conduction band near the interface of the InGaN barrier and the AlInGaN EBL is only slightly deformed due to the reduced density of the po-larization charges. Relatively small electron accumulation at the AlInGaN EBL is observed, and the AlInGaN energy barrier rel-ative to the electron quasi-Fermi level is about 130 meV for 40% polarization.
Fig. 4 shows the vertical electron current profile within the ac-tive regions of laser structures with AlGaN and AlInGaN EBLs at 500-mA injection current. The positions of the two quantum wells are marked with gray areas. The left-hand side of the figure is the n-side of the device. The electron current is injected from the n-type layers into the quantum wells and recombines with holes in the quantum wells. Therefore, the electron current den-sity is reduced in the quantum wells. An electron current, which overflows through the quantum wells, is viewed as the leakage current. In Fig. 4(a), the vertical electron current profile of the laser diodes with different EBLs is nearly identical when the built-in polarization is not considered. As for the calculation re-sults with consideration of the 40% polarization, the electron current profiles of these two laser structures are obviously dif-ferent [Fig. 4(b)]. It is found that the electron leakage current of the laser structure with the AlGaN EBL is relatively larger than that of the laser structure with the AlInGaN EBL due to the lower barrier height at the InGaN/AlGaN interface. Fig. 5 shows the stimulated recombination rate for laser structures with
Fig. 4. Vertical electron current profile for laser structures with AlGaN and AlInGaN EBLs at 500-mA injection current. (a) 0% polarization. (b) 40% polarization.
Fig. 5. Stimulated recombination rate for laser structures with AlGaN and AlInGaN EBLs at 500-mA injection current. (a) 0% polarization. (b) 40% polarization.
AlGaN and AlInGaN EBLs at 500-mA injection current when the polarization values are considered with 0% [Fig. 5(a)] and 40% [Fig. 5(b)], respectively. In Fig. 5(a), the stimulated recom-bination rate of laser diodes with different EBLs is nearly iden-tical when the built-in polarization is not considered. However, by taking the 40% polarization into account, the stimulated re-combination rate of the laser diode with the AlGaN EBL is rela-tively lower than that of the laser diode with the AlInGaN EBL, as shown in Fig. 5(b). Therefore, the large electron leakage cur-rent induced by the lower barrier height at the InGaN/AlGaN interface of the laser diode with the AlGaN EBL lowers the stim-ulated recombination rate in the quantum wells. By employing
Fig. 6. Percentage of electron leakage current versus built-in polarization charges for laser diodes with AlGaN and AlInGaN EBLs.
Fig. 7. Laser threshold current versus percentage of built-in polarization charges for laser diodes with AlGaN and AlInGaN EBLs.
the AlInGaN EBL, the electron leakage current obviously de-creases, and the stimulated recombination rate can significantly be enhanced.
In order to further understand the effects of the built-in polar-ization on the electron leakage current, the percentage of elec-tron leakage current versus built-in polarization charges for laser diodes with AlGaN and AlInGaN EBLs is shown in Fig. 6. The percentage of the electron leakage current is defined as the ratio of the electron current overflowed to the p-type layer to that injected into the active region of the laser diodes. Since the effective energy barrier provided by the AlGaN EBL is re-duced with increasing polarization charges, the percentage of the electron leakage current increases with the amount of po-larization charges as well. The difference of the percentage of the electron leakage between the laser structures with AlGaN and AlInGaN EBLs becomes more obvious with increasing po-larization charges. In the case of no popo-larization, the electron leakage of the laser structure with the AlInGaN EBL is slightly larger than that of the laser structure with the AlGaN EBL. It is attributed to the difference of conduction-band offset between the InGaN barrier layer and the EBLs. Note that the energy bar-riers provided by the AlGaN and AlInGaN EBLs are 264 and 242 meV, respectively. Although the same band offset ratio is considered in our simulation, the conduction- and valence-band edges will be modified by strain effects. Therefore, after taking this effect on the bandgap of the EBL into account, the energy barrier created by the AlInGaN EBL is lower, which leads to a
slightly larger electron leakage when the built-in polarization is omitted.
Fig. 7 shows the laser threshold current versus built-in polarization charges for the laser structures with the AlGaN and AlInGaN EBLs. In the condition of no polarization, the threshold current of the laser structure with the AlInGaN EBL is slightly smaller than that of the laser structure with the AlGaN EBL even though the electron leakage is larger, as shown in Fig. 6. To understand this simulation result, we compare the quantum-well optical confinement factors of the two laser structures. The calculated results show that the quantum-well optical confinement factor of the laser structure with the AlInGaN EBL is larger than that of the laser structure with the AlGaN EBL due to the higher refractive index of the AlInGaN layer. The values of the quantum-well optical confinement factors are 1.2% and 1.6% for laser structures with AlGaN and AlInGaN EBLs, respectively. Furthermore, the threshold current becomes higher with increasing built-in polarization, owing to the increase of electron leakage current. The improve-ment of the threshold current for InGaN quantum-well laser with AlInGaN EBL is more obvious for high level of built-in polarization. Therefore, according to the simulation results, the InGaN quantum-well lasers using a quaternary AlInGaN EBL can effectively inhibit the electron leakage current and lower the threshold current when the built-in polarization is taken into account in our simulation.
V. CONCLUSION
In conclusion, the built-in polarization of the EBL plays an important role in the InGaN quantum-well lasers. The large amount of polarization charges at the interface between the InGaN barrier layer and the conventional AlGaN EBL are found to dramatically enhance the electron leakage and cause an additional increase in the threshold current. In order to reduce this polarization effect, the InGaN quantum-well lasers with AlGaN and AlInGaN EBLs are systematically investigated in this paper. By comparing the effects of the electron leakage and the threshold current of the laser structures with different EBLs, the simulation results suggest that the laser performance can be markedly improved by employing the quaternary AlInGaN EBL. In the meantime, the simulation results also show that the quantum-well optical confinement factor increases for the laser structure with an AlInGaN EBL due to its higher refractive index when compared to the conventional AlGaN EBL.
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Jun-Rong Chen was born in Taichung, Taiwan,
R.O.C., on October 23, 1980. He received the B.S. degree in physics from the National Changhua Uni-versity of Education (NCUE), Changhua, Taiwan, in 2004 and the M.S. degree in optoelectronics from the Institute of Photonics, NCUE, in 2006. He is currently working toward the Ph.D. degree in the Department of Photonics and Institute of Electro-Optical Engineering, National Chiao Tung University (NCTU), Hsinchu, Taiwan.
He joined the Semiconductor Laser Technology Laboratory, NCTU, in 2006, where he was engaged in research on III-V semiconductor materials for light-emitting diodes and on semiconductor lasers
under the instruction of Prof. Tien-Chang Lu, Prof. Hao-Chung Kuo, and Prof. Shing-Chung Wang. His recent research interests include III-nitride semiconductor lasers, epitaxial growth of III-nitride materials, and numerical simulation of III-V optoelectronic devices.
Chung-Hsien Lee was born in Taiwan, R.O.C. He received the B.S. degree
in physics from Tamkang University, Taipei, Taiwan, in 2005. He is currently working toward the M.S. degree in optoelectronics at the Institute of Photonics, National Changhua University of Education (NCUE), Changhua, Taiwan.
He has been with the Laboratory of Lasers and Optical Semiconductors, NCUE, since 2005, where he has been engaged in research on III-V semicon-ductor materials for light-emitting diodes and on semiconsemicon-ductor lasers under the instruction of Prof. Yen-Kuang Kuo. His recent research interests include III-nitride semiconductor lasers, vertical-cavity surface-emitting lasers, and light-emitting diodes.
Tsung-Shine Ko was born in Tainan, Taiwan,
R.O.C., in 1978. He received the B.S. degree in physics from the National Changhua University, Changhua, Taiwan, in 2001 and the M.S. degree in atomic science from the National Tsing Hau University, Hsinchu, Taiwan, in 2004. Since 2004, he has been working toward the Ph.D. degree at the Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu.
After he received the B.S. degree in 2001, he was a Practice Teacher for one year with. He was engaged in research on the design of masks for extreme ultraviolet, the synthesis of gold nanoparticles, and the growth of Si/Ge nanostructures under the instruction of Dr. J. Shieh, Prof. H. L. Chen, and Prof. T. C. Chu. His current research in-terests include the fabrication of nanostructure oxide materials and the epitaxial growth of nonpolar GaN-based materials under the instruction of Prof. T. C. Lu, Prof. H. C. Kuo, and Prof. S. C. Wang.
Yi-An Chang was born in Taipei, Taiwan, R.O.C.,
on March 13, 1978. He received the B.S. and M.S. degrees in physics from the National Changhua Uni-versity of Education (NCUE), Changhua, Taiwan, in 2001 and 2003, respectively. He is currently working toward the Ph.D. degree at the Institute of Electro-op-tical Engineering, National Chiao Tung University, Hsinchu, Taiwan.
He was with the Laboratory of Lasers and Optical Semiconductors, NCUE, in 2000, where he was en-gaged in research on passive Q-switching with solid-state saturable absorbers and III-nitride semiconductor materials for light-emit-ting diodes and semiconductor lasers under the instruction of Prof. Yen-Kuang Kuo. His current research interests include III-nitride and InGaAsN semicon-ductor devices and infrared vertical-cavity surface-emitting lasers under the in-struction of Prof. Hao-Chung Kuo and Prof. Shing-Chung Wang.
Tien-Chang Lu (M’07) received the B.S. degree
in electrical engineering from the National Taiwan University, Taipei, Taiwan, R.O.C., in 1995, the M.S. degree in electrical engineering from the University of Southern California, Los Angeles, in 1998, and the Ph.D. degree in electrical engineering and computer science from the National Chiao Tung University, Hsinchu, Taiwan, in 2004.
He was with the Union Optronics Corporation as a Manager of Epitaxy Department in 2004. Since August 2005, he has been with the National Chiao Tung University as a member of the faculty in the Department of Photonics. His research work included the design, epitaxial growth, process, and characteriza-tion of optoelectronic devices such as Fabry–Perot-type semiconductor lasers, vertical-cavity surface-emitting lasers, resonant-cavity light-emitting diodes (LEDs), wafer-fused flip-chip LEDs, solar cells, etc. He has been engaged in
the low-pressure MOCVD epitaxial technique associated with various material systems including InGaAlAs, InGaAsP, AlGaAs, InGaAlP, and InGaAlN as well as the corresponding process skills. He is also interested in the structure design and simulations for optoelectronic devices using computer-aided software.
Hao-Chung Kuo (S’98–M’99–SM’06) received the
B.S. degree in physics from the National Taiwan Uni-versity, Taipei, Taiwan, R.O.C., in 1990, the M.S. de-gree in electrical and computer engineering from Rut-gers University, Camden, NJ, in 1995, and the Ph.D. degree in electrical and computer engineering from the University of Illinois at Urbana–Champaign in 1999.
He has an extensive professional career both in re-search and industrial rere-search institutions, which in-cludes as follows: Research Consultant with Lucent Technologies, Bell Lab, Holmdel, NJ, (from 1995 to 1997), R&D Engineer with the Fiber-optics Division, Agilent Technologies (from 1999 to 2001), and R&D Manager with LuxNet Corporation (from 2001 to 2002). Since September 2002, he has been with the National Chiao Tung University, Hsinchu, Taiwan, as a member of the faculty at the Institute of Electro-Optical Engineering. He has authored or coauthored over 60 publications. His current research interests include the epitaxy, design, fabrication, and measurement of high-speed InP-and GaAs-based vertical-cavity surface-emitting lasers, as well as GaN-based lighting-emitting devices and nanostructures.
Yen-Kuang Kuo was born in Chia-Yi, Taiwan,
R.O.C., on July 19, 1959. He received the B.S. degree in electrophysics from the National Chiao Tung University, Hsinchu, Taiwan, in 1982, the M.S. degree in electrical engineering from the National Taiwan University, Taipei, Taiwan, in 1984, and the Ph.D. degree in electrical engineering from the University of Southern California (USC), Los Angeles, in 1994.
From 1984 to 1991, he was with the Aeronautical Research Laboratory, Chung Shan Institute of Science and Technology, Taichung, Taiwan. He was a Postdoctoral Research Fellow with the Center for Laser Studies, USC, from 1994 to 1995, where he was engaged in research on passive Q-switching with solid-state saturable absorbers. From 1995 to 1997, he was with the Aerospace Industrial Develop-ment Corporation, Taichung. Since 1997, he has been a member of the faculty in the Department of Physics, National Changhua University of Education, Changhua, Taiwan, where he is currently a Professor with the Department of Physics and Institute of Photonics and also the Head of the Laboratory of Lasers and Optical Semiconductors. His current research interests include passive Q-switching with solid-state saturable absorbers and semiconductor materials for light-emitting diodes, organic light-emitting diodes, and semiconductor lasers.
Shing-Chung Wang (M’79–SM’03–LM’07)
re-ceived the B.S. degree in electrical engineering from the National Taiwan University, Taipei, Taiwan, R.O.C., the M.S. degree in electrical engineering from the National Tohoku University, Sendai, Japan, and the Ph.D. degree in electrical engineering from the Stanford University, Stanford, CA, in 1971.
He has an extensive professional career both in academic and industrial research institutions, which includes as follows: member of the faculty at the National Chiao Tung University, Hsinchu, Taiwan (from 1965 to 1967), Research Associate with Stanford University (from 1971 to 1974), Senior Research Scientist with Xerox Corporation (from 1974 to 1985), and Consulting Scientist with Lockheed-Martin Palo Alto Research Lab-oratories (from 1985 to 1995). Since 1995, he has been a member of the faculty at the Institute of Electro-Optical Engineering, National Chiao Tung University. He has authored or coauthored over 160 publications. His current research interests include semiconductor lasers, vertical-cavity surface-emitting lasers, blue and UV lasers, quantum-confined optoelectronic structures, optoelectronic materials, diode-pumped lasers, and semiconductor-laser applications.
Prof. Wang is a fellow of the Optical Society of America and the recipient of the Outstanding Scholar Award from the Foundation for the Advancement of Outstanding Scholarship.
