Influence of growth parameters on the properties of InGaN/GaN multiple quantum well grown by metalorganic chemical vapor deposition

The effects of growth parameters such as barrier growth time, growth pressure and indium flow rate on the properties of InGaN/GaN multiple quantum wells (MQWs) were investigated by using photoluminescence (PL), high resolution X-ray diffraction (HRXRD), and atomic force microscope (AFM). The InGaN/GaN MQW structures were grown on c-plane sapphire substrate by using metalorganic chemical vapor deposition. With increasing barrier growth time, the PL peak energy is blue-shifted by 18 nm. For InGaN/GaN MQW structures grown at different growth pressures, the PL intensity is maximized in the 300 Torr – grown structure, which could be attributed to the improved structural quality confirmed by HRXRD and AFM results. Also, the optical properties of InGaN/GaN MQW are strongly affected by the indium flow rate.     

InGaN/GaN多量子阱的组分确定和晶格常数计算

采用金属有机化学气相沉积(MOCVD)技术以蓝宝石为衬底在n型GaN单晶层上生长了InGaN/GaN多量子阱结构外延薄膜，利用高分辨X射线衍射(HRXRD)，卢瑟福背散射/沟道(RBS/channeling)，以及光致发光(PL)技术对InGaN/GaN多量子阱结构薄膜分别进行了平均晶格常数计算、In原子替位率计算和In组分的定量分析.研究表明：InGaN/GaN多量子阱的水平和垂直方向平均晶格常数分别为a_epi=0.3195nm，c_epi=0.5198nm，In原子的替位率为99.3%，利用HRXRD和RBS/channeling两种分析技术计算In的组分分别是0.023和0.026，并与样品生长时设定的预期目标相符合，验证了两种实验方法的准确性；而用室温条件下的光致发光谱(PL)来计算InGaN/GaN多量子阱中In的组分是与HRXRD和RBS/channeling的实验结果相差很大，说明用PL测试In组分的方法是不适宜的. 关键词： InGaN/GaN多量子阱 高分辨X射线衍射 卢瑟福背散射/沟道 光致发光     

InN分凝的InGaN薄膜的光致发光与吸收谱

我们用低压MOCVD在蓝宝石衬底生长了InGaN/GaN外延层.用X射线衍射(XRD),光致发光谱(PL),光吸收谱等测量手段,研究了InGaN的辐射发光机制.In组分利用Vegard定理和XRD测量得到.我们发现随着In组分的增加,在光吸收谱上发现吸收边的红移和较宽的Urbach带尾;PL谱中低能端的发射渐渐成为主导,并且在PL激发谱中InGaN峰也变宽.我们认为压电效应改变了InGaN的能带结构,从而影响了光学吸收特性.而在InN量子点中的辐射复合则是InGaN层发光的起源.     

Laser reflectometry in situ monitoring of InGaAs grown by atmospheric pressure metalorganic vapour phase epitaxy

InGaAs layers on undoped GaAs (0 0 1) substrates were grown by atmospheric pressure metalorganic vapour phase epitaxy (AP-MOVPE). In order to obtain films with different indium composition (x_In), the growth temperature as a growth parameter, was varied from 420 to 680 °C. Furthermore, high-resolution X-ray diffraction (HRXRD) measurements were used to quantify the change of x_In. Crystal quality has been also studied as a function of growth conditions. On the other hand, laser reflectometry (LR) at 632.8 nm wavelength, was employed to in situ monitor epitaxy. Reflectivity-time signal was enabled to evaluate structural and optical properties of samples. We have fitted experimental data to determine optical constants and growth rate of InGaAs at 632.8 nm. In addition, the fitting provided InGaAs thickness as a function of growth time. Based on ex situ characterization by scanning electronic microscopy (SEM) and HRXRD, we propose a practical method, relating the contrast of first reflectivity maximum with the X-ray diffraction peak angular difference between the substrate and epitaxial layer, to determine in situ the In solid composition in InGaAs alloys.     

Influence of Si doping on the structural and optical properties of InGaN epilayers

Influences of the Si doping on the structural and optical properties of the InGaN epilayers are investigated in detail by means of high-resolution X-ray diffraction （HRXRD）, photolumimescence （PL）, scanning electron microscope （SEM）, and atomic force microscopy （AFM）. It is found that the Si doping may improve the surface morphology and crystal quality of the InGaN film and meanwhile it can also enhance the emission efficiency by increasing the electron concentration in the InGaN and suppressing tile formation of V-defects, which act as nonradiative recombination centers in the InGaN, and it is proposed that the former plays a more important role in enhancing the emission efficiency in the InGaN.     

Combined effects of carrier scattering and Coulomb screening on photoluminescence in InGaN/GaN quantum well structure with high In content

Photoluminescence(PL) spectra of two different green InGaN/GaN multiple quantum well(MQW) samples S1 and S2,respectively with a higher growth temperature and a lower growth temperature of InGaN well layers are analyzed over a wide temperature range of 6 K-3 30 K and an excitation power range of 0.001 mW-75 mW.The excitation power-dependent PL peak energy and linewidth at 6 K show that in an initial excitation power range,the emission process of the MQW is dominated simultaneously by the combined effects of the carrier scattering and Coulomb screening for both the samples,and both the carrier scattering effect and the Coulomb screening effect are stronger for S2 than those for S1;in the highest excitation power range,the emission process of the MQWs is dominated by the filling effect of the high-energy localized states for S1,and by the Coulomb screening effect for S2.The behaviors can be attributed to the fact that sample S2 should have a higher amount of In content in the InGaN well layers than S1 because of the lower growth temperature,and this results in a stronger component fluctuation-induced potential fluctuation and a stronger well/barrier lattice mismatchinduced quantum-confined Stark effect.This explanation is also supported by other relevant measurements of the samples,such as temperature-dependent peak energy and excitation-power-dependent internal quantum efficiency.     

Influence of barrier thickness on the structural and optical properties of InGaN/GaN multiple quantum wells

The structural and optical properties of InGaN/GaN multiple quantum wells(MQWs) with different barrier thicknesses are studied by means of high resolution X-ray diffraction(HRXRD), a cross-sectional transmission electron microscope(TEM), and temperature-dependent photoluminescence(PL) measurements. HRXRD and cross-sectional TEM measurements show that the interfaces between wells and barriers are abrupt and the entire MQW region has good periodicity for all three samples. As the barrier thickness is increased, the temperature of the turning point from blueshift to redshift of the S-shaped temperature-dependent PL peak energy increases monotonously, which indicates that the localization potentials due to In-rich clusters is deeper. From the Arrhenius plot of the normalized integrated PL intensity, it is found that there are two kinds of nonradiative recombination processes accounting for the thermal quenching of photoluminescence,and the corresponding activation energy(or the localization potential) increases with the increase of the barrier thickness.The dependence on barrier thickness is attributed to the redistribution of In-rich clusters during the growth of barrier layers,i.e., clusters with lower In contents aggregate into clusters with higher In contents.     

Effects of strain-compensated AlGaN/InGaN superlattice barriers on the optical properties of InGaN light-emitting diodes

In this article, metalorganic chemical vapor deposition (MOCVD)-grown InGaN multiple-quantum-well (MQW) light-emitting diodes (LEDs) with Al_0.03Ga_0.97N and Al_0.03Ga_0.97N/In_0.01Ga_0.99N superlattices-barrier layers on c-plane sapphire were studied for the influence of the strain-compensated barrier on the optical properties of the LEDs. High-resolution X-ray diffraction (HRXRD) analysis shows that the LEDs with a strain-compensated superlattice barrier (SC-SLB) have better interface quality than those using AlGaN. This difference in quality may result from the alleviation of strain relaxation in superlattice layers to improve the crystalline perfection of the epitaxial structures. It was also found that the degree of the exciton localization effect rises considerably as InGaN grows directly on the AlGaN barrier layers. However, the increase in the strength of the polarization fields within the MQWs (as evaluated from bias-dependent photoluminescence (PL) measurement) could reduce the radiative efficiency of the LEDs and shift their PL peaks toward long wavelengths. With suitable control of crystalline quality and the reduced quantum-confined Stark effect in the MQWs, the SC-SLB LEDs operating at 150-mA-current show a 22.3% increase in light output power as compared to their conventional counterparts.     

Magnesium doping in InAlAs and InGaAs/Mg films lattice-matched to InP grown by MOVPE

Mg-doped InAlAs and InGaAs films were grown at 560 °C lattice matched to InP semi-insulting substrate by metalorganic vapor phase epitaxy (MOVPE) under various Cp₂Mg flow conditions. Hall effect, photoluminescence (PL), high-resolution X-ray diffraction (HR-XRD), and secondary ion mass (SIMS) were the tools used in this work. The crystalline quality and the n-p conversion of the InAlAs and InGaAs/Mg films are described and discussed in relation to the Cp₂Mg flow. Distinguishing triple emission peaks in PL spectra is observed and seems to be strongly dependent on the Cp₂Mg flow. SIMS is employed to analyze the elements in the epitaxial layers. The variation of indium and magnesium components indicates a decrease of magnesium incorporation during the growth of InAlAs layers leading to a contracted lattice. In addition, the magnesium incorporation in the InGaAs lattice during growth has been confirmed by SIMS.     

蓝光激光器结构中InGaN/GaN多量子阱界面效应的精细光致发光光谱研究

金属有机化学气相沉积(MOCVD)方法制备InGaN/GaN多量子阱结构时,在GaN势垒层生长的N2载气中引入适量H2,能够有效改善阱/垒界面质量从而提升发光效率.本工作利用光致发光(PL)光谱技术,对蓝光激光器结构中的InGaN/GaN多量子阱的发光性能进行了精细的光谱学测量与表征,研究了通H2生长对量子阱界面的调控...     

Photoluminescence and Raman scattering in spatially inhomogeneous heteroepitaxial InGaN layers

Spatial inhomogeneities of the indium distribution in In _x Ga_1–x N epitaxial layers grown on sapphire substrate with a GaN buffer layer were investigated using photoluminescence (PL) in addition to confocal scanning Raman spectroscopy (RS) and PL. Broad emission bands from In-enriched InGaN nanoclusters (700–900 nm) and from the volume outside the clusters (about 460 nm) were observed in PL spectra of an epitaxial InGaN layer with an average In content of 25.7%. It was established that larger micro-PL intensities corresponded to energetically shallower clusters. The observed broadly asymmetric A₁(LO) RS band of InGaN confirmed that the In concentration in the layer was highly variable. Modeling the LO phonon band by two Lorentzian curves gave an average In concentration of 21% in the volume outside the clusters and 37% in the nanoclusters, which was considerably higher than the average concentration in the layer and agreed well with their PL band positions.     

Atmospheric-pressure metal–organic vapor-phase epitaxy of GaAsBi alloys on high-index GaAs substrates

We investigated the growth characteristics and properties of GaAsBi layers grown by atmospheric-pressure metal–organic vapor-phase epitaxy on different GaAs substrate orientations. The surface morphology of GaAsBi alloys was investigated by means of scanning electron microscopy. The structural and optical properties of the alloys were examined using high-resolution X-ray diffraction (HRXRD) and photoreflectance spectroscopy, respectively. HRXRD results show that the GaAsBi growth rate was significantly lower on (1 1 5)A than on (0 0 1), (1 1 1)A and (1 1 4)A GaAs. The highest Bi content was obtained for GaAsBi layers grown on (1 1 5)A GaAs substrates.     

Temperature dependent growth of InGaN/GaN single quantum well

InGaN/GaN single quantum well (SQW) structures under various InGaN growth temperatures have been grown by metal organic chemical vapor deposition (MOCVD), the surface morphologies and optical properties are investigated. The radius of the typical V-pits on the SQW surface is affected by the InGaN well-temperature, and the surface roughness decreased as the well-temperature reduced. Room-temperature photoluminescence (PL) and cathode luminescence (CL) shows the quantum well and quantum dot (QD)-like localized state light emission of the SQWs grown at 700 and 690 °C, respectively, whereas the samples grown at 670 and 650 °C present hybrid emission peaks. Excitation power dependent PL spectra indicates the QD-like localized state emission dominates at low excitation power and the quantum well emission starts to take over at high excitation power.     

Fabrication and optical properties of InGaN/GaN multiple quantum well light emitting diodes with amorphous BaTiO3 ferroelectric film

BaTiO3 （BTO） ferroelectric thin films are prepared by the sol,el method. The fabrication and the optical properties of an InGaN/GaN multiple quantum well light emitting diode （LED） with amorphous BTO ferroelectric thin film are studied. The photolumineseence （PL） of the BTO ferroelectric film is attributed to the structure. The ferroeleetric film which annealed at 673 K for 8 h has the better PL property. The peak width is about 30 nm from 580 nm to 610 nm, towards the yellow region. The mixed electroluminescence （EL） spectrum of InGaN/GaN multiple quantum well LED with 150-nm thick amorphous BTO ferroelectric thin film displays the blue-white light. The Commission Internationale De L＇Eclairage （CIE） coordinate of EL is （0.2139, 0.1627）. EL wavelength and intensity depends on the composition, microstructure and thickness of the ferroelectric thin film. The transmittance of amorphous BTO thin film is about 93% at a wavelength of 450 nm-470 nm. This means the amorphous ferroelectrie thin films can output more blue-ray and emission lights. In addition, the amorphous ferroelectric thin films can be directly fabricated without a binder and used at higher temperatures （200 ℃-400 ℃）. It is very favourable to simplify the preparation process and reduce the heat dissipation requirements of an LED. This provides a new way to study LEDs.     

Growth of In0.52Al0.48As on InP substrates by molecular beam epitaxy: some effects of V/III flux ratio variation

Growth of In_0.52Al_0.48As epitaxial layers on InP(100) substrates by molecular beam epitaxy at a wide range of arsenic overpressure (V/III flux ratio from 30 to 300) is carried out. Analysis performed using low-temperature photoluminescence (PL) and double-axis X-ray diffraction (XRD) showed a strong and prominent dependence of the PL and XRD linewidths on the V/III flux ratio. Under our growth conditions, both the PL and XRD linewidths exhibit a minimum point at a V/III flux ratio of 150 which corresponds to a maximum in the PL intensity and XRD intensity ratio. Flux ratios exceeding 150 results in an increase in both the PL and XRD linewidths corresponding to a reduction in their associated intensities. Room-temperature Raman scattering measurements show a narrowing in the InAs-like and AlAs-like longitudinal-optic (LO) phonon linewidths which broaden at high flux ratios, while the LO phonon frequencies exhibit a gradual reduction as the flux ratio is increased. PL spectrum taken at increasing temperature show a quenching of the main emission peak followed by the evolution of a broad lower energy emission which is possibly associated with deep-lying centres. This effect is more prominent in samples grown at lower V/III flux ratios. Hall effect measurements showed a gradual reduction in the mobility in correspondence to an increase in the electron concentration as the flux ratio is increased.     

应力导致InAs/In0.15Ga0.85As量子点结构中In0.15Ga0.85As阱层的合金分解效应研究

利用固源分子束外延技术，在In_0.15Ga_0.85As/GaAs量子阱生长了两个InAs/In_0.15Ga_0.85As量子点(DWELL)样品.通过改变其中一个InAs DWELL样品中的In_0.15Ga_0.85As阱层的厚度和生长温度，获得了量子点尺寸增大而且尺寸分布更均匀的结果.结合光致发光光谱(PL)和压电调制光谱(PzR)实验结果，发现该样品量子点的光学性质也同时得到 关键词： 合金分解效应 0.15Ga_0.85As量子点')" href="#">InAs/In_0.15Ga_0.85As量子点 光致发光光谱 压电调制光谱     

硅衬底生长的InGaN/GaN多层量子阱中δ型硅掺杂n-GaN层对载流子复合过程的调节作用

为了解决在单晶硅衬底上生长的InGaN/GaN多层量子阱发光二极管器件发光效率显著降低的问题,使用周期性δ型Si掺杂的GaN取代Si均匀掺杂的GaN作为n型层释放多层界面间的张应力。采用稳态荧光谱及时间分辨荧光谱测量,提取并分析了使用该方案前后的多层量子阱中辐射/非辐射复合速率随温度（10~300 K）的变化规律。实验结果表明引入δ-Si掺杂的n-GaN层后,非辐射复合平均激活能由（18±3）meV升高到（38±10）meV,对应非辐射复合速率随温度升高而上升的趋势变缓,室温下非辐射复合速率下降,体系中与阱宽涨落有关的浅能级复合中心浓度减小,PL峰位由531 nm左右红移至579 nm左右,样品PL效率随温度的衰减受到抑制。使用周期性δ型Si掺杂的GaN取代Si均匀掺杂的GaN作为生长在Si衬底上的InGaN/GaN多层量子阱LED器件n型层,由于应力释放,降低了多层量子阱与n-GaN界面、InGaN/GaN界面的缺陷密度,使得器件性能得到了改善。     

Epitaxial Nd-doped α-(Al(1-x)Ga(x))2O3 films on sapphire for solid-state waveguide lasers

Single-crystal aluminum-gallium oxide films have been grown by molecular beam epitaxy in the corundum phase. Films of the (Al(1-x)Ga(x))(2)O(3) alloys doped with neodymium have favorable properties for solid-state waveguide lasers, including a high-thermal-conductivity sapphire substrate and a dominant emission peak in the 1090-1096 nm wavelength range. The peak position is linearly correlated to the unit cell volume, which is dependent on film composition and stress. Varying the Ga-Al alloy composition during growth will enable the fabrication of graded-index layers for tunable lasing wavelengths and low scattering losses at the interfaces.     

MOCVD生长的InGaN合金的发光特性

研究了用金属有机化学气相沉积(MOCVD)法在蓝宝石基底上生长的InGaN样品的发光特性。样品XRD谱中存在InGaN、In、InN相,表明样品中存在相分离;透射谱能看到由于F-P腔调制引起的震荡;相对氙灯激发发光谱,激光激发的发光谱其发光峰位置发生蓝移。由于样品上下表面形成F-P腔,对发光谱产生强烈的调制,在较高强度激发下,在室温下带边峰分成三个峰,其中波长较短的两个发光峰表现出相同的特征,其发光机制可能为以In量子点为局域中心的局域化激子复合发光,而波长较长的发光峰,是一个超线性受激发光峰,其发光机制可能是电子-空穴等离子的散射。不同温度的PL谱表明两个主要的发光峰表现出不同的温度特征,利用F-P干涉理论分析可知,当温度高于120K后样品折射率随着温度的升高而增大。     

纳米β-FeSi2/a-Si多层膜室温光致发光分析

采用射频磁控溅射的方法,在Si（100）基片上制备了纳米β-FeSi₂/Si多层结构,利用X射线衍射、透射电子显微镜、光致发光光谱等表征技术,研究了β-FeSi₂/Si多层结构的结构、成分和光致发光特性.研究结果表明：利用磁控溅射法得到的Fe/Si多层膜,室温下能够检测到β-FeSi₂的1.53 μm处光致发光信号;未退火时多层膜是（非晶的FeSi₂+β-FeSi₂颗粒）/非晶Si结构,退火后则是 关键词： 2')" href="#">β-FeSi₂ 磁控溅射 XRD 光致发光光谱