INFLUENCES OF ALLOY DISORDER AND INTERFACE ROUGHNESS ON OPTICAL-SPECTRA OF INGAAS/GAAS STRAINED-LAYER QUANTUM-WELLS

We present studies of alloy composition and layer thickness dependences of excitonic linewidths in InGaAs/GaAs strained-layer quantum wells grown by MBE, using both photoluminescence and optical absorption. It is observed that linewidths of exciton spectra increase with indium content and well size. Using the virtual crystal approximation, the experimental data are analyzed. The results obtained show that the alloy disorder is the dominant mechanism for line broadening at low temperature. In addition, it is found that the absorption spectra related to light hole transitions have varied from a peak to a step-like structure as temperature increases. This behavior can be understood by the indirect space transitions of light holes.

Aggregation and precipitation in high dose as ion implanted Ge0.5Si0.5 alloy

Thermally stimulated redistribution and precipitation of excess arsenic in Ge0.5Si0.5 alloy has been studied by X-ray photoelectron spectroscopy (XPS), cross sectional transmission electron microscopy (XTEM) and X-ray energy disperse spectrometry (EDS). Samples were prepared by the implantation of 6 X 10(6) As+ cm(-2) and 100 keV with subsequent thermal processing at 800 degrees C and 1000 degrees C for 1 h. The XPS depth profiles from the implanted samples before and after the thermal annealing indicate that there is marked redistribution of the elements in heavily arsenic-implanted Ge0.5Si0.5 alloys during the annealing, including: (1) diffusion of As from the implanted region to the surface; (2) aggregation of Ge in the vicinity of the surface. A high density of precipitates was observed near the surface which were by XTEM and EDS identified as an arsenide. It is suggested that most of the implanted As in Ge0.5Si0.5 alloy exists in the form of GeAs.

射频分子束外延生长AlInGaN四元合金

利用射频等离子体辅助分子束外延(RF-MBE)技术在蓝宝石衬底上外延了铝铟镓氮(AlInGaN)四元合金,通过改变Al源的束流生长了不同组分的AlInGaN四元合金,材料生长过程中采用反射式高能电子衍射(RHEED)进行了在位检测.通过扫描电镜(SEM)、卢瑟福背散射(RBS)、X射线衍射(XRD)和阴极荧光(CL)等测试手段表征了AlInGaN四元合金的结构和光学特性.研究结果表明:在GaN层上生长AlInGaN外延层时,外延膜呈二维生长;当铝炉的温度为920℃时,外延AlInGaN四元合金外延薄膜中Al/In接近4.7,X射线衍射摇摆曲线的半高宽最小为5arcmin,四元合金的阴极荧光发光峰的半高宽为25nm,AlInGaN四元合金外延层具有较好的晶体质量和光学质量.

Resonant Raman Scattering and Photoluminescence Emissions from Above Bandgap Levels in Dilute GaAsN Alloy

The transitions of E0 ,E0 ＋A0, and E＋ in dilute GaAs（1-x） Nx alloys with x = 0.10% ,0.22% ,0.36% ,and 0.62% are observed by micro-photoluminescence. Resonant Raman scattering results further confirm that they are from the intrinsic emissions in the studied dilute GaAsN alloys rather than some localized exciton emissions in the GaAsN alloys. The results show that the nitrogen-induced E E＋ and E0 ＋ A0 transitions in GaAsN alloys intersect at a nitrogen content of about 0.16%. It is demonstrated that a small amount of isoelectronic doping combined with micro-photoluminescence allows direct observation of above band gap transitions that are not usually accessible in photoluminescence.

Metal-organic Vapor Phase Epitaxy Growth and Characterization of InAlGaN Epilayers

In order to improve crystal quality for growth of quaternary InAlGaN, a series of InAlGaN films were grown on GaN buffer layer under different growth temperatures and carrier gases by low-pressure metal-organic vapor phase epitaxy. Energy dispersive spectroscopy (EDS) was employed to measure the chemical composition of the quaternary, high resolution X-ray diffraction (HRXRD) and photoluminescence (PL) technique were used to characterize structural and optical properties of the epilayers, respectively. The PL spectra of InAlGaN show with and without the broad-deep level emission when only N2 and a N2+H2 mixture were used as carrier gas, respectively. At pressure of 1.01×104 Pa and with mixed gases of nitrogen and hydrogen as carrier gas, different alloy compositions of the films were obtained by changing the growth temperature while keeping the fluxes of precursors of indium (In), aluminum (Al), gallium (Ga) and nitrogen (N2) constant. A combination of HRXRD and PL measurements enable us to explore the relative optimum growth parameters-growth temperature between 850℃ and 870℃,using mixed gas of N2+H2 as carrier gas.

AlInGaN材料的生长及其光学性质的研究

研究AlInGaN材料的生长特性及其光学性质.通过对不同生长温度生长的三个AlInGaN样品的测量,发现In的掺入量随着生长温度的降低而增加,而Al的掺入几乎没什么变化;在较低温度下生长的材料具有较好的材料质量与光学特性,其原因直接与In组分的掺入有关,In组分的掺入可以减少材料的缺陷,改善材料的质量.同时,用时间分辨光谱研究了AlInGaN材料的发光机理,发现其发光强度随时间变化(荧光衰退寿命)不是指数衰减,而是一种伸展的指数衰减.通过对这种伸展的指数衰减特性的研究,发现AlInGaN发光来自于局域激子的复合,且这种局域化中心呈现量子点的特性,延伸指数衰减行为是由不同局域态之间的局域激子的跳跃(hopping)造成的.此外,进一步研究了荧光衰退寿命随发光能量的变化关系和发光的辐射复合和非辐射复合特性,进一步证实了局域化中心的量子点特性.

AlInGaN合金的发光机制研究

用变温光致发光谱和时间分辨光谱研究了AlInGaN合金的发光机制。实验结果表明，发光强度随时间并不是呈指数衰减关系，而可以用伸展指数哀减函数来描述，表明材料中存在明显的无序。形成这种无序的原因是In组分不均产生的微结构(如量子点)。伸展衰减函数中弥散指数β不仅随温度变化，在250K也不随辐射能量变化，表明载流子的弥散过程由局域态之间的跳跃所主导。进一步实验表明局域态在250K时仍然表现出零维特性。

Metalorganic Chemical Vapor Deposition of GaNAs Alloy Using Dimethylhydrazine as Nitrogen Precursor

GaNAs alloy is grown by metalorganic chemical vapor deposition (MOCVD) using dimethylhydrazine (DMHy) as the nitrogen precursor. High-resolution X-ray diffraction (HRXRD) and secondary ion mass spectrometry (SIMS) are combined in determining the nitrogen contents in the samples. Room temperature photoluminescence (RTPL) measurement is also used in characterizing. The influence of different Ga precursors on GaNAs quality is investigated. Samples grown with triethylgallium (TEGa) have better qualities and less impurity contamination than those with trimethylgallium (TMGa). Nitrogen content of 5.688% is achieved with TEGa. The peak wavelength in RTPL measurement is measured to be 1278.5nm.

Characterization of Ga N_x As_(1 - x) Alloy Grownon Ga As by Molecular Beam Epitaxy

集成光电子学国家重点实验室基金,国家863计划,国家自然科学基金,中科院项目

Effect of rapid thermal annealing on the Raman spectrum of Si0.33Ge0.67/Si (100) alloy

The effect of thermal annealing on the Raman spectrum of Si0.33Ge0.67 alloy grown on Si (100) by molecular beam epitaxy is investigated in the temperature range of 550-800 degrees C. For annealing below 700 degrees C, interdiffusion at the interface is negligible and the residual strain plays the dominant role in the Raman shift. The strain-shift coefficients for Si-Ge and Ge-Ge phonon modes are determined to be 915 +/- 215 cm(-1) and 732 +/- 117 cm(-1), respectively. For higher temperature annealing, interdiffusion is significant and strongly affects the Raman shift and the spectral shape.

Pressure behavior of Te isoelectronic centers in S-rich ZnS1-xTex alloy

The photoluminescence from ZnS1-xTex alloy with 0 < x < 0.3 was investigated under hydrostatic pressure up to 7 GPa. Two peaks were observed in the alloys with x < 0.01, which are related to excitons bound to isolated Te isoelectronic impurities (Te-1 centers) and Te pairs (Te-2 centers), respectively. Only the Te-2 related emissions were observed in the alloys with 0.01 < x < 0.03. The emissions in the alloys with 0.03 < x < 0.3 are attributed to the excitons bound to the Te-n (n greater than or equal to 3) cluster centers. The pressure coefficient of the Te-1 related peak is 89(4) meV/GPa, about 40% larger than that of the band gap of ZnS. On the other hand, the pressure coefficient of the Te-2 related emissions is only 52(4) meV/GPa, about 15% smaller than that of the ZnS band gap. A simple Koster-Slater model has been used to explain the different pressure behavior of the Te-1 and Te-2 centers. The pressure coefficient of the Te-3 centers is 62(2) meV/GPa. Then the pressure coefficients of the Te-n centers decrease rapidly with further increasing Te composition.

Strain relaxation of GeSi alloy with low dislocation density grown on low-temperature Si buffers

We have developed a low-temperature (LT) growth technique. Even with Ge fraction x upto 90%, the total thickness of fully relaxed GexSi1-x buffers can he reduced to 1.7 mu m with dislocation density lower than 5 x 10(6) cm(-2). The surface roughness is no more than 6 nm. The strain relaxation is quite inhomogeneous From the beginning. Stacking faults generate and form the mismatch dislocations in the interface of GeSi/LT-Si. (C) 1999 Elsevier Science B.V. All rights reserved.