Room-Temperature Continuous-Wave Operation of InGaN-Based Blue-Violet Laser Diodes with a Lifetime of 15.6 Hours

We report our recent progress of investigations on InGaN-based blue-violet laser diodes (LDs). The room-temperature (RT) cw operation lifetime of LDs has extended to longer than 15.6 h. The LD structure was grown on a c-plane free-standing (FS) GaN substrate by metal organic chemical vapor deposition (MOCVD). The typical threshold current and voltage of LD under RT cw operation are 78 mA and 6.8 V, respectively. The experimental analysis of degradation of LD performances suggests that after aging treatment, the increase of series resistance and threshold current can be mainly attributed to the deterioration of p-type ohmic contact and the decrease of internal quantum efficiency of multiple quantum well (MQW), respectively.

Abnormal photoabsorption in high resistance GaN epilayer

Unintentionally doped GaN epilayers are grown by the metalorganic chemical vapor deposition (MOCVD). Photovoltaic (PV) spectroscopy shows that there appears an abnormal photoabsorption in some undoped GaN films with high resistance. The peak energy of the absorption spectrum is smaller than the intrinsic energy band gap of GaN. This phenomenon may be related to exciton absorption. Then metal-semiconductor-metal (MSM) Schottky photodetectors are fabricated on these high resistance epilayers. The photo spectrum responses are different when the light individually irradiates each of the two electrodes with the photodetector which are differently biased. When the excitation light irradiates around the reverse biased Schottky junction, the responsivity is almost one order of magnitude larger than that around the forward biased junction. Furthermore, when the excitation light irradiates the reverse biased Schottky junction, the peak energy of the spectrum has a prominent red-shift compared with the peak energy of the spectrum measured with the excitation light irradiating the forward biased Schottky junction. The shift value is about 28 meV, and it is found to be insensitive to temperature. According to the analyses of the distribution of the electric field within the MSM device and the different dependences of the response on the electric field intensity between the free carriers and excitons, a reliable explanation for the different response among various areas is proposed.

GROWTH OF GASB AND GAASSB IN THE SINGLE-PHASE REGION BY MOVPE

GaSb layers are grown on GaSb substrates; the effects of input partial pressure of trimethylantimony and the V/III ratio are studied. A model of the MOVPE phase diagram for the growth of GaSb and GaAsxSb1-x is developed which assumes thermodynamic equilibrium to be established at the solid-vapor interface.

Stoichiometric defects in semi-insulating GaAs

The influences of arsenic interstitials and dislocations on the lattice parameters of undoped semi-insulating (SI) GaAs single crystals were analyzed. It was shown that the dislocations in such crystals serve as effective gettering sites for arsenic interstitials due to the deformation energy of dislocations. The average excess arsenic in GaAs epilayers grown by molecular-beam epitaxy (MBE) at low temperatures (LT) is about 1%, and the lattice parameters of these epilayers are larger than those of liquid-encapsulated Czochralski-grown (LEG) SI-GaAs by about 0.1%. The atomic ratio, [As]/([Ga] + [As]), in SI-GaAs grown by low-pressure (LP) LEC is the nearest to the strict stoichiometry compared with those grown by high-pressure (HP) LEC and vertical gradient freeze (VGF). After multiple wafer annealing (MWA), the crystals grown by HPLEC become closer to be strictly stoichiometric.

Assessment of the structural properties of GaAs/Si epilayers using X-ray (004) and (220) reflections

We improved the method previously used to determine the lattice constants and misorientation of GaAs/Si by recording the patterns of X-ray (004) and (220) reflections. The (220) reflection was measured from the (110) cross section of a GaAs/Si epilayer. The structural properties of the GaAs/Si epilayers grown by metal-organic chemical-vapor deposition (MOCVD) using an ultrathin a-Si buffer layer were investigated. The rotation angle of GaAs/Si epilayers grown by MOCVD using an a-Si buffer layer is very small and the lattice constants of these GaAs/Si epilayers agree quite well with elastic theory.

New observation on the luminescence of CdS clusters in zeolite-Y

The excitation spectrum of CdS dusters in zeolite-Y is consistent with their absorption spectrum, both showing two absorption bands that are assigned to the Is-is and Is-lp transitions, respectively. A new emission at 400 nn is considered to be the recombination of the bounded excitons. The emission firstly increases then decreases with increasing cluster size or loading. The emission by excitation into the Is-is band is stronger and sharper than that by excitation into the Is-lp band. This phenomenon is attributed to the size inhomogeneity and the strong electron-phonon interaction of the dusters. Copyright (C) 1996 Elsevier Science Ltd

Characterization and improvement of GaAs layers grown on Si using an ultrathin a-Si film as a buffer layer

GaAs epilayers grown on Si by metalorganic chemical vapor deposition (MOCVD) using an ultrathin a-Si buffer layer were characterized by deep-level transient spectroscopy (DLTS). Six electron traps with activation energies of 0.79, 0.67, 0.61, 0.55, 0.53 and 0.32 eV below the conduction band were determined by fitting the experimental spectra. Two of the levels, C (0.61 eV) and F (0.32 eV), were first detected in GaAs epilayers on Si and identified as the metastable defects M3 and M4, respectively. In order to improve the quality of GaAs/Si epilayers, another GaAs layer was grown on the GaAs/Si epilayers grown using MOCVD. The deep levels in this regrown GaAs epilayer were also studied using DLTS. Only the EL2 level was found in the regrown GaAs epilayers. These results show that the quality of the GaAs epilayer was greatly improved by applying this growth process.

PHOTOLUMINESCENCE SPECTRUM STUDY OF THE GAAS/SI EPILAYER GROWN BY USING A THIN AMORPHOUS SI FILM AS BUFFER LAYER

Recently, we reported successful growth of high-quality GaAs/Si epilayers by using a very thin amorphous Si film as buffer layer. In this paper, the impurity properties of this kind of GaAs/Si epilayers have been studied by using PL spectrum, SIMS and Hall measurement. Compared to a typical PL spectrum of the GaAs/Si epilayers grown by conventional two-step method, a new peak was observed in our PL spectrum at the energy of 1.462 eV, which is assigned to the band-to-silicon acceptor recombination. The SIMS analysis indicates that the silicon concentration in this kind of GaAs/Si epilayers is about 10(18) cm(-3). But its carrier concentration (about 4 x 10(17) cm(-3)) is lower than the silicon concentration. The lower carrier concentration in this kind of GaAs/Si epilayer can be interpreted both as the result of higher compensation and as the result of the formation of the donor-defect complex. We also found that the high-quality and low-Si-concentration GaAs/Si epilayers can be regrown by using this kind of GaAs/Si epilayer as substrate. The FWHM of the X-ray (004) rocking curve from this regrowth GaAs epilayer is 118 '', it is much less than that of the first growth GaAs epilayer (160 '') and other reports for the GaAs/Si epilayer grown by using conventional two-step method (similar to 200 '').

METAL-ORGANIC CHEMICAL-VAPOR-DEPOSITION GROWTH OF GAN

Single-crystal GaN films have been deposited on (01 (1) over bar 2) sapphire substrates using trimethylgallium (TMGa) and NH3 as sources. The morphological, crystalline, electrical and optical characterizations of GaN film are investigated. The carrier concentration ofundoped GaN increases with decreasing input NH3-to-TMGa molar flow ratio.

OPS-VECSEL芯片的生长与光谱研究

光泵浦半导体垂直外腔面发射激光器(OPS-VECSEL)是一种新型激光器,在很多领域都具有广阔的应用前景.采用MOCVD生长了工作波长为980 nm的VECSEL芯片,测量了芯片X射线衍射(XRD)图谱,光致发光(PL)谱和反射谱,结果表明,芯片生长的准确性较高.同时采用物理光学的理论结合实际模型,运用矩阵分析方法计算了VECSEL的反射谱,计算结果与实验结果吻合良好.最后,通过对不同窗口层厚度的纵向增强因子的计算和分析得到了共振结构具有高的峰值增强,反共振结构具有大的增益带宽.在理论上提出,对于该OPS-VECSEL结构,采用共振和反共振结构之间的窗口厚度可以使其稳定工作在特定波长而又不严格限制增益带宽.

带非吸收窗口的大功率657 nm半导体激光器

在激光器腔面处制作非吸收窗口(NAW)可以有效地减少光吸收,防止激光器过早出现光学灾变损伤(COD),是提高大功率半导体激光器的功率特性的重要手段之一.采用金属有机化学气相沉积(MOCVD)技术二次外延生长了大功率657 nm红光半导体激光器结构,通过闭管扩散Zn的方法在腔面附近制作了非吸收窗口.实验发现扩散温度550 ℃,扩散时间20 min时,得到的非吸收窗口最为有效,激光器连续工作的无扭折输出功率大于100 mW,超过常规的无窗口结构激光器的最大输出功率的两倍,激光器的斜率效率提高了23%.测量该类器件的温度特性发现,环境温度为20～70 ℃时,其输出功率均可大于50 mW,计算得到激光器的特征温度约为89 K,波长增加率约为0.24 nm/℃.

GaInP/GaAs/Ge三结叠层光电池光谱响应的温度特性

利用金属有机物化学气相沉积法(MOCVD)制备了转化效率达27.1%的GaInP/GaAs/Ge三结叠层电池,并对其光谱响应的温度特性进行了测量研究.通过光谱响应曲线观察到各子电池的吸收边随温度升高发生红移,这主要归因于电池材料禁带宽度的变窄效应.根据光谱响应数据计算得到的GaInP/GaAs/Ge叠层电池各子电池在室温下的短路电流密度分别为12.9,13.7和17 mA/cm~2,且叠层电池的短路电流密度的温度系数为8.9 μA/(cm~2·℃).最后,根据叠层电池的串联结构推导了其电压温度系数为-6.27 mV/℃.

GaN基垂直腔面发射激光器的研制

作者在我国大陆首次实现了GaN基垂直腔面发射激光器（VCSEL）的激射．首先采用金属有机物化学气相沉积（MOCVD）技术在蓝宝石衬底上进行高质量氮化物增益区的外延生长．然后在表面沉积高反射介质膜分布布拉格反射镜（DBR）．将样品键合到其它支撑片上后，采用激光剥离技术将蓝宝石衬底去除．再在去除蓝宝石后露出的氮化物表面沉积第二组介质膜DBR制成VCSEL．在室温光泵条件下，观察到VCSEL的激射．激射波长449．5nm。阈值6．5mJ／cm~2．激射峰的半高宽小于0．1nm，这些指标达到了国际领先水平．本文为进一步研制实用化氮化物VCSEL奠定了重要的基础．

Low-Temperature Growth of ZnO Films on GaAs by Metal Organic Chemical Vapor Deposition

ZnO thin films were grown on GaAs （001） substrates by metal-organic chemical vapor deposition （MOCVD） at low temperatures ranging from 100 to 400℃. DEZn and 1-12 O were used as the zinc precursor and oxygen precursor, respectively. The effects of the growth temperatures on the growth characteristics and optical properties of ZnO films were investigated. The X-ray diffraction measurement （XRD） results indicated that all the thin films were grown with highly c- axis orientation. The surface morphologies and crystal properties of the films were critically dependent on the growth temperatures. Although there was no evidence of epitaxial growth, the scanning electron microscopy （SEM） image of ZnO film grown at 400℃ revealed the presence of ZnO microcrystallines with closed packed hexagon structure. The photoluminescence spectrum at room temperature showed only bright band-edge （3. 33eV） emissions with little or no deep-level e- mission related to defects.

Zn-doped InGaAs Base Heterojunction Bipolar Transistors Grown by Low Pressure Metal Organic Chemical Vapor Deposition

High performance InP/InGaAs heterojunction bipolar transistors(HBTs) have been widely used in high-speed electronic devices and optoelectronic integrated circuits. InP-based HBTs were fabricated by low pressure metal organic chemical vapor deposition(MOCVD) and wet chemical etching. The sub-collector and collector were grown at 655 ℃ and other layers at 550 ℃. To suppress the Zn out-diffusion in HBT, base layer was grown with a 16-minute growth interruption. Fabricated HBTs with emitter size of 2.5×20 μm~2 showed current gain of 70~90, breakdown voltage(BV_(CE0))>2 V, cut-off frequency(f_T) of 60 GHz and the maximum relaxation frequency(f_(MAX)) of 70 GHz.