InGaN/GaN多量子阱的变温发光特性研究

采用低压金属有机化学沉积方法制备了InGaN/GaN多量子阱.变温PL测量发现,量子阱发光强度具有良好的温度稳定性,随着温度升高(10～300K),发光强度只减小到1/3左右.分析认为,InGaN/GaN多量子阱的多峰发光结构是由多量子阱的组分及阱宽的不均匀引起的.随着温度升高,GaN带边及量子阱的光致发光均向低能方向移动,但与GaN带边不同,量子阱发光峰值变化并不与通过内插法得到的Varshni经验公式相吻合,而是与InN带边红移趋势一致,分析了导致这种现象的可能因素.还分析了量子阱发光寿命随温度升高而减小的原因.     

InGaN/GaN多量子阱电池的垒层结构优化及其光学特性调控

InGaN基量子阱作为太阳电池器件的有源区时,垒层厚度设计以及实际生长对其光学特性的影响极为重要.采用金属有机化学气相沉积(MOVCD)技术,在蓝宝石衬底上外延生长了垒层厚度较厚的InGaN/GaN多量子阱,使用高分辨X射线衍射和变温光致发光谱研究了垒层厚度对InGaN多量子阱太阳电池结构的界面质量、量子限制效应及其光学特性的影响.较厚垒层的InGaN/GaN多量子阱的周期重复性和界面品质较好,这可能与垒层较薄时对量子阱的生长影响有关.同时,厚垒层InGaN/GaN多量子阱的光致发光光谱峰位随温度升高呈现更为明显的“S”形(红移-蓝移-红移)变化,表现出更强的局域化程度和更高的内量子效率.     

GaN基量子阱激子结合能和激子光跃迁强度

采用变分法,计算了GaN基量子阱中激子结合能和激子光跃选强度。计算结果表明,GaN基量子阱中激子结合能为10－55meV,大于体材料中激子结合能,并随着阱宽减小而增加,在临界阱宽处达到最大。结间带阶同样对激子结合能有着较大的影响,更大带阶对应更大的结合能。同时量子限制效应增加了电子空穴波函数空间重叠,因此加强了激子光跃迁振子强度,导致GaN/AlN量子阱中激子光吸收明显强于体材料中激子光吸收。     

快速热退火对InGaAsSb/AlGaAsSb多量子阱材料发光特性的影响

I型InGaAsSb/AlGaAsSb量子阱是1.8～3μm波段锑化物半导体激光器的首选材料,为进一步提升分子束外延生长的InGaAsSb/AlGaAsSb量子阱材料的光学性能,本文对其进行了快速热退火处理,通过光致发光光谱研究了快速热退火对量子阱材料光致发光特性的影响。光致发光光谱测试结果表明,快速热退火会使量子阱结构中垒层、阱层异质界面处的原子互扩散,改善量子阱材料的晶体质量,促使结构释放应力,进而提高了量子阱材料的光学性能。随着退火温度升高,量子阱材料的室温光致发光谱峰位逐渐蓝移,在500,550,600℃退火后,量子阱材料光致发光谱的峰位分别蓝移了7,8,9 meV。通过变温及变功率光致发光光谱测试,确认了样品发光峰的来源,位于0.687 eV的发光峰为局域载流子的复合,位于0.701 eV的发光峰为自由激子的复合。对不同退火温度的样品进一步研究后发现,退火温度的升高降低了材料中局域态载流子复合的比例,在600℃退火温度下局域载流子与自由激子的强度比值降为500℃退火温度下的22.6%,这表明合适温度的快速热退火处理可以有效改善量子阱材料的光致发光特性。     

掺氮ZnSe外延层的光致发光研究

报导了掺氮ＺｎＳｅ外延层的光致发光,研究了与氮受主有关的发光峰随温度和激发强度的变化关系．１０Ｋ下施主－受主对发光峰随激发强度的增加向高能方向移动,且峰强呈现饱和趋势．在１０～３００Ｋ温度范围光致发光谱表明,随着温度增加,由于激子在受主束缚激子态和施主束缚激子态之间转移,施主束缚激子发光峰强度相对受主束缚激子发光峰强度增加     

生长温度对InGaN/GaN多量子阱LED光学特性的影响

利用低压MOCVD系统,在蓝宝石衬底上外延生长了InGaN/GaN多量子阱蓝紫光LED结构材料.研究了生长温度对有源层InGaN/GaN多量子阱的合金组分、结晶品质及其发光特性的影响.结果表明当生长温度从730℃升到800℃时,LED的光致发光波长从490nm移到380nm,室温下PL谱发光峰的半高全宽从133meV降到73meV,表明了量子阱结晶性的提高.高温生长时,PL谱中还观察到了GaN的蓝带发光峰,说明量子阱对载流子的限制作用有所减弱.研究表明,通过改变生长温度可以对LED发光波长及有源层InGaN的晶体质量实现良好的控制.     

InGaN/GaN和InGaN/AlGaN多量子阱中应变对光致发光特性的影响

对蓝宝石衬底上的InGaN/GaN和InGaN/AlGaN多量子阱结构和经激光剥离去除衬底的InGaN/GaN和InGaN/AlGaN多量子阱结构薄膜样品,进行了光致发光谱、高分辨XRD和喇曼光谱测量.PL测量结果表明,相对于带有蓝宝石衬底的样品,InGaN/GaN多量子阱薄膜样品的PL谱峰值波长发生较小的蓝移,而InGaN/AlGaN多量子阱薄膜样品的PL谱峰值波长发生明显的红移;喇曼光谱的结果表明,激光剥离前后E2模的峰值从569.1减少到567.5cm-1.这说明激光剥离去除衬底使得外延层整体的压应力得到部分释放,但InGaN/GaN与InGaN/AlGaN多量子阱结构中阱层InGaN的应力发生了不同的变化.XRD的结果证实了这一结论.     

InGaN/GaN和InGaN/AlGaN多量子阱中应变对光致发光特性的影响

对蓝宝石衬底上的InGaN/GaN和InGaN/AlGaN多量子阱结构和经激光剥离去除衬底的InGaN/GaN和InGaN/AlGaN多量子阱结构薄膜样品,进行了光致发光谱、高分辨XRD和喇曼光谱测量.PL测量结果表明,相对于带有蓝宝石衬底的样品,InGaN/GaN多量子阱薄膜样品的PL谱峰值波长发生较小的蓝移,而InGaN/AlGaN多量子阱薄膜样品的PL谱峰值波长发生明显的红移;喇曼光谱的结果表明,激光剥离前后E2模的峰值从569.1减少到567.5cm-1.这说明激光剥离去除衬底使得外延层整体的压应力得到部分释放,但InGaN/GaN与InGaN/AlGaN多量子阱结构中阱层InGaN的应力发生了不同的变化.XRD的结果证实了这一结论.     

ZnCdSe/ZnSe单量子阱中的双激子发光谱

在分子束外延生长的ＺｎＣｄＳｅ／ＺｎＳｅ单量子阱结构中,观察到了双激子发光谱．采用不同宽度的量子阱,得出了双激子束缚能与量子阱宽度的依赖关系．研究了双激子发光谱与激发光波长和激发功率的关系．发现在阱内激发的条件下,自由激子更容易由于相互作用而形成双激子,在～１ｍＷ／ｃｍ２的激发功率密度下即可观察到明显的双激子发光．     

InGaN/GaN 和 InGaN/AlGaN 多量子阱中应变对光致发光特性的影响

对蓝宝石衬底上的InGaN/GaN和InGaN/AlGaN多量子阱结构和经激光剥离去除衬底的InGaN/GaN和InGaN/AlGaN多量子阱结构薄膜样品，进行了光致发光谱、高分辨XRD和喇曼光谱测量. PL测量结果表明，相对于带有蓝宝石衬底的样品，InGaN/GaN多量子阱薄膜样品的PL谱峰值波长发生较小的蓝移，而InGaN/AlGaN多量子阱薄膜样品的PL谱峰值波长发生明显的红移；喇曼光谱的结果表明，激光剥离前后E2模的峰值从569.1减少到567.5cm-1. 这说明激光剥离去除衬底使得外延层整体的压应力得到部分释放，但InGaN/GaN与InGaN/AlGaN多量子阱结构中阱层InGaN的应力发生了不同的变化. XRD的结果证实了这一结论.     

Exciton wavefunction coupled surface plasmon resonance for In-rich InGaN film with perforated aluminum cylindrical micropillar arrays

The optical characterization of excitons coupled with surface plasmon resonance (SPR) for InGaN/GaN heterostructures with perforated cylindrical micropillar arrays is investigated. We analyze the optical characteristics of excitons coupled with SPR for InGaN/GaN heterostructures with perforated cylindrical micropillars, as shown in measurements of the photoluminescence (PL) spectra over a broad range of temperatures between 20 and 300 K. From the temperature-dependent PL spectra, we observe the better SPR coupling effects, resulting in less carrier confinement in the InGaN energy band. The magnitude of the redshift of the emission peak shown by the sample with the coated aluminum (Al) pattern is larger than that shown by the sample with no metal film. This was due to the presence of more exciton coupling surface plasmons within the Al/InGaN interface. The enhancement of the PL intensity of the sample with the deposited Al pattern film can be attributed to a stronger SPR coupling interaction with the excitons. The experimental results indicate that a perforated Al cylindrical micropillar array can significantly affect carrier confinement, enhancing the quantum efficiency of Al/In-rich InGaN heterostructures due to the interaction of the SPR coupling effect between the InGaN quantum dot-like region and the Al film.     

掺硅InGaN和掺硅GaN的光学性质的研究

采用光致发光方法研究了采用金属有机化学气相沉积(MOCVD)在蓝宝石衬底上生长的掺硅InGaN和掺硅CaN材料的光学性质。在室温下．InGaN材料带边峰位置为437．0nm，半高宽为14．3nm；GaN材料带边峰位置为363．4nm．半高宽为9．5nm。进行变温测量发现．随温度的升高．两种材料的发光强度降低，半高宽增大；GaN材料的带边峰值能量位置出现红移现象．与Varshini公式符合较好；InGaN材料的带边峰值能量位置则出现红移-蓝移-红移现象．这与InGaN材料的局域态、热效应以及由于电子-空穴对的形成而造成的无序程度增加有关．对大于140K的峰值能量位置的红移用Varshini公式拟合．符合较好。     

Structural and Optical Properties of ZnO Nanotips Grown on GaN Using Metalorganic Chemical Vapor Deposition

ZnO nanotips are grown on epitaxial GaN/c-sapphire templates by metalorganic chemical vapor deposition. X-ray diffraction (XRD) studies indicate that the epitaxial relationship between ZnO nanotips and the GaN layer is (0002)ZnO||(0002)GaN and (101̄0)ZnO||(101̄0)GaN. Temperature-dependent photoluminescence (PL) spectra have been measured. Sharp free exciton and donor-bound exciton peaks are observed at 4.4 K with photon energies of 3.380 eV, 3.369 eV, and 3.364 eV, confirming high optical quality of ZnO nanotips. Free exciton emission dominates at temperatures above 50 K. The thermal dissociation of these bound excitons forms free excitons and neutral donors. The thermal activation energies of the bound excitons at 3.369 eV and 3.364 eV are 11 meV and 16 meV, respectively. Temperature-dependent free A exciton peak emission is fitted to the Varshni’s equation to study the variation of energy bandgap versus temperature.     

多层In_(0.55)Al_(0.45)As/A_(0.5)Ga_(0.5)As量子点的变温光致发光研究

测量了自组织多层In0.55Al0.45As/Al0.5Ga0.5As量子点的变温光致发光谱,同时观察到来自浸润层和量子点的发光,首次直接观察到了浸润层和量子点之间的载流子热转移.分析发光强度随温度的变化发现浸润层发光的热淬灭包括两个过程:低温时浸润层的激子从局域态热激发到扩展态,然后被量子点俘获;而温度较高时则通过势垒层的X能谷淬灭.利用速率方程模拟了激子在浸润层和量子点间的转移过程,计算结果与实验符合得很好     

Efficient near IR photoluminescence from gallium nitride layers doped with arsenic

Photoluminescence in the 1.2–1.4 eV spectral range from GaN:As layers grown on (0001) Al₂O₃ substrates was observed and studied. The photoluminescence is attributed to radiative recombination in GaAs nanocrystallites, self-organized in the GaN matrix during growth. The photoluminescence intensity attains a maximum at a growth temperature of ～780°C, which is explained by the competition between several temperature-dependent processes that affect the formation of GaAs nanocrystallites. Sharp emission lines were observed at the high-energy edge of the photoluminescence band. These lines are caused by an emission of bound excitons in the GaAs nanocrystallites and by phonon replicas of the bound-exciton emission. The energies of the corresponding optical phonons are typical of GaAs. The photoluminescence-excitation spectra exhibit features related to resonantly excited free and bound excitons as well as to excitons formed simultaneously with the emission of optical phonons.     

Optical Properties of Silicon—doped InGaN and GaN Layers

The optical properties of Silicon—doped InGaN and GaN grown on sapphire by MOCVD have been investigated by photoluminescence (PL) method. At room temperature, the band—gap peak of InGaN is 437.0 nm and its full width of half—maximum (FWHM) is about 14.3 nm. The band—gap peak and FWHM for GaN are 364.4 nm and 9.5 nm, respectively. By changing the temperature from 20 K to 293 K, it is found that the PL intensity of samples decreases but the FWHM broadens with the increasing of the temperature.GaN sample shows red—shift, InGaN sample shows red—blue—red—shift. The temperature dependence of peak energy shift is studied and explained.     

Temperature-dependent electroluminescence in InGaN/GaN multiple-quantum-well light-emitting diodes

We present a comparative study on temperature dependence of electroluminescence (EL) of InGaN/GaN multiple-quantum-well (MQW) light-emitting diodes (LEDs) with identical structure but different indium contents in the active region. For the ultraviolet (UV) and blue LEDs, the EL intensity decreases dramatically with decreasing temperature after reaching a maximum at 150 K. The peak energy exhibits a large redshift in the range of 20–50 meV with a decrease of temperature from 200 K to 70 K, accompanying the appearance of longitudinal-optical (LO) phonon replicas broadening the low energy side of the EL spectra. This redshift is explained by carrier relaxation into lower energy states, leading to dominant radiative recombination at localized states. In contrast, the peak energy of the green LED exhibits a minimal temperature-induced shift, and the emission intensity increases monotonically with decreasing temperature down to 5 K. We attribute the different temperature dependences of the EL to different degrees of the localization effects in the MQW regions of the LEDs.     

Photoluminescence characteristics of GaN/lnGaN/GaN quantum wells

Photoluminescence (PL) characteristics of GaN/lnGaN/GaN single quantum wells (QWs) and an InGaN/GaN single heterojunction were studied using continuous wave (CW) and pulsed photoluminescence in both edge and surface emitting configurations. Samples were grown on c-plane sapphire substrates by atmospheric pressure metalorganic chemical vapor deposition (MOCVD). Room temperature and 77K PL measurements were performed using a CW Ar-ion laser (305 nm) and a frequency tripled (280 nm), pulsed, mode-locked Ti: sapphire laser. CW PL emission spectra from the quantum wells (24, 30, 80Å) were all blue shifted with respect to the reference sample. The difference (i. e., the blue shift) between the measured value of peak emission energy from the QW and the band-edge emission from the reference sample was attributed to quantum size effects, and to strain arising due to a significant lattice mismatch between InGaN and GaN. In addition, stimulated emission was observed from an InGaN/GaN single heterojunction in the edge and surface emitting configu-ration at 77K. The narrowing of emission spectra, the nonlinear dependence of output emission intensity on input power density, and the observation of a strongly polarized output are presented.     

Temperature dependence of performance of InGaN/GaN MQW LEDs with different indium compositions

The temperature dependence of performance of InGaN/GaN multiple-quantum-well (MQW) light-emitting diodes (LEDs) with different indium compositions in the MQWs was investigated. With increasing In composition in the MQWs, the optical performance of the LEDs at room temperature was increased due to an increase in the localized energy states caused by In composition fluctuations in MQWs. As the temperature was increased, however, the decrease in output power for LED with a higher In composition in the MQWs was higher than that of LED with a lower In composition in the MQWs. This could be due to the increased nonradiation recombination through the high defect densities in the MQWs resulted from the increased accumulation of strain between InGaN well and GaN barrier.     

Growth of InxGa(1−x)N compound semiconductors and high-power InGaN/AlGaN double heterostructure violet-light-emitting diodes

In_xGa(_1−x)N films were grown on GaN films with an indium mole fraction x up to X = 0.33 at temperatures between 720°C and 850°C. The growth rate of InGaN films had to be decreased sharply to obtain high-quality InGan films when the growth temperature was decreased. Band-gap energies between 2.67 eV and 3.40 eV obtained by room-temperature photoluminescence measurements fit quite well to parabolic forms previously obtained by Osamura et al. on the indium mole fraction x assuming that the band-gap energies for GaN and InN are 3.40 and 1.95 eV, respectively. High-power InGaN/AlGaN double-heterostructure violet-light-emitting diodes were fabricated. The typical output power was 1000 μW and the external quantum efficiency was as high as 1.5% at a forward current of 20 mA at room temperature. The peak wavelength and the full width at half-maximum of the electroluminescence were 380 nm and 17 nm, respectively.