Comparison study of GaN films grown on porous and planar GaN templates

The GaN thick films have been grown on porous GaN template and planar metal-organic chemical vapor deposition(MOCVD)-GaN template by halide vapor phase epitaxy(HVPE). The analysis results indicated that the GaN films grown on porous and planar GaN templates under the same growth conditions have similar structural, optical, and electrical properties. But the porous GaN templates could significantly reduce the stress in the HVPE-GaN epilayer and enhance the photoluminescence(PL) intensity. The voids in the porous template were critical for the strain relaxation in the GaN films and the increase of the PL intensity. Thus, the porous GaN converted from β-Ga2O3 film as a novel promising template is suitable for the growth of stress-free GaN films.     

Origin,characteristics, and suppression of residual nitrogen in MPCVD diamond growth reactor

Unintentional nitrogen incorporation has been observed in a set of microwave plasma chemical vapor deposition (MPCVD)-grown samples. No abnormality has been detected on the apparatus especially the base pressure and feeding gas purity. By a comprehensive investigation including the analysis of the plasma composition, we found that a minor leakage of the system could be significantly magnified by the thermal effect, resulting in a considerable residual nitrogen in the diamond material. Moreover, the doping mechanism of leaked air is different to pure nitrogen doping. The dosage of several ppm of pure nitrogen can lead to efficient nitrogen incorporation in diamond, while at least thousands ppm of leaked air is required for detecting obvious residual nitrogen. The difference of the dosage has been ascribed to the suppression effect of oxygen that consumes nitrogen. As the unintentional impurity is basically detrimental to the controllable fabrication of diamond for electronic application, we have provided an effective way to suppress the residual nitrogen in a slightly leaked system by modifying the susceptor geometry. This study indicates that even if a normal base pressure can be reached, the nitrogen residing in the chamber can be "activated" by the thermal effect and thus be incorporated in diamond material grown by a MPCVD reactor.     

Effect of Rapid Thermal Annealing on the Formation of In-N Clusters in Strained InGaNAs

A model for the effect of rapid thermal annealing on the formation of In-N clusters in strained GalnNAs is developed according to thermodynamics. In the model, the lowest annealing temperature influencing the redistribution of atoms is introduced. The average variation of energy for formation per In-N bond is obtained by fitting the experimental values. Using the present model, we calculate the average number of nearest-neighbor In atoms per N atom after annealing. The obtained results are compared with the experiment. The qualitative analysis and quantitative analysis are in good agreement with each other. The model is helpful to explain the essence of the blueshift caused by annealing.     

UV Light-Emitting Diodes at 340nm Fabricated on a Bulk GaN Substrate

We demonstrate an ultra-violet light-emitting diode （UV-LED） fabricated on a bulk GaN substrate with elec- troluminescence （EL） emission centered at about 340 nm. The UV-LED exhibits low reverse leakage current on the order of 10^-9 A under -5 V at room temperature, which can be explained by the low defect density in the epi-structure. The evolution of EL spectra as a function of injection current levels reveals the improved heat dissipation of the LEDs with vertical geometry on the bulk GaN substrate. The unusual increase of EL intensity at elevated temperatures can be explained by thermally assisted p-dopant ionization.     

Optical and Structural Properties of Cr-Doped GaN Grown by HVPE Method

Single crystalline Cr-doped GaN fihns are successfully grown by hydride vapor phase epitaxy. The structure analysis indicates that the film is uniform without detectable Cr precipitates or clusters and the Cr atoms are substituted for Ga sites. The impurity modes in the range 510 530cm^-1 are observed by the Raman spectra. The modes are assigned to the host lattice defects caused by substitutional Cr. The donor-aeceptor emission is found to locate at Ec - 0.20 eV by analyzing the photoluminescence spectrum obtained at different temperatures, and the emission is attributed to the structural defects caused by CrGa-VN complex. The superconductor quantum interference device results show that the Cr-doped GaN film without detectable Cr precipitates or clusters exhibits paramagnetic properties.     

利用金属有机物化学气相沉积技术生长的a面GaN表面形貌和位错的研究

采用金属有机物化学气相淀积技术在r面蓝宝石衬底上制备了a面GaN薄膜,用熔融的KOH在400 ℃对样品分别腐蚀1.0,1.5和2.0 min.用扫描电镜、原子力显微镜、X射线衍射谱和阴极射线荧光对腐蚀前后的表面形貌进行分析.研究表明,400 ℃下腐蚀1.5 min后出现了长平行四边形的条纹状,这是由于无极化的a面GaN表面极性各向异性,c向与m向上N原子悬挂键密度不同,同时稳定性不同,对OH^-离子的吸附能力不同造成的,其中沿c方向易于腐蚀.同时,a面GaN腐蚀后出现了六角突起.我们认为这与穿透位错有关,而其形貌则与GaN薄膜的位错局部极性有关. 关键词： a面GaN')" href="#">a面GaN 堆垛层错 极性     

表面钝化前后Al0.22Ga0.78N/GaN异质结势垒层应变的高温特性

用高分辨X射线衍射仪(HRXRD)研究了表面钝化前后Al0.22Ga0.78N/GaN异质结势垒层应变的高温特性,温度变化范围从室温到813K.结果表明,对未钝化的异质结,当测试温度高于523K时,Al0.22Ga0.78N势垒层开始出现应变弛豫;钝化后,在Al0.22Ga0.78N势垒层中会产生一个附加的平面拉伸应变,并随着温度的增加,势垒层中的平面拉伸应变会呈现出一个初始的增加,接着应变将减小,对100nm厚的Al0.22Ga0.78N势垒层,应变只是轻微地减小,但对于50nm厚的Al0.22Ga0.78N势垒层,则出现了严重的应变弛豫现象.     

GaN1-xPx薄膜的结构特性研究

用金属有机物化学气相沉积技术在蓝宝石衬底上外延了高P组分的GaN1-xPx 薄膜.利用x射线衍射仪和拉曼光谱仪研究了P对GaN1-xPx晶体结构的影响.研究结果表明:随着P组分比的增加,GaN1-xPx(0002)衍射峰逐渐向小角度移动,即晶格常数变大;与非掺杂GaN相比,GaN1-xPx薄膜的拉曼光谱中出现了4个新的振动模式,将它们分别归因于P族团引起的准局部振动模式、Ga-P键振动引起的间隙模,以及来自缺陷引起的无序激活散射.同时,随着P组分比的增加,A1(LO)模式的频率向低频方向移动,这种红移现象起因于合金化和应变的影响.     

GaN1-xPx薄膜的结构特性研究

用金属有机物化学气相沉积技术在蓝宝石衬底上外延了高P组分的GaN_1-xP _x 薄膜.利用x射线衍射仪和拉曼光谱仪研究了P对GaN_1-xP_x晶体结构 的影响.研究结果表明：随着P组分比的增加，GaN_1-xP_x（0002）衍射 峰逐渐向小角度移动，即晶格常数变大；与非掺杂GaN相比，GaN_1-xP_x薄 膜的拉曼光谱中出现了4个新的振动模 关键词： 1-xP_x')" href="#">GaN_1-xP_x 金属有机物化学气相沉积 x射线衍射 拉曼光谱     

Strain and Phonon Confinement in Self－Assembled Ge Quantum Dot Superlattices Superlattices ＊

Raman scattering measurements were carried out in self-assembled Ge quantum dot superlattices grown bymolecular beam epitaxy. The characteristics of the Ge-Ge, Si-Ge, Si-SiLoc and Si-Si peaks were investigated,especially the Ge-Ge optical phonon frequency shift was emphasized, which was tuned by the phonon confinementand strain effects. The experimentally observed frequency shift values of the Ge-Ge peak frequency caused byoptical phonon confinement and strain in Ge quantum dots were discussed with quantitative calculations.