Development of Photo-Voltaic Cells using III-V Alloy Semiconductors for Thermo-Photo-Voltaic Applications (2004)

正在进行的研究的主要目标是开发新的技术，以生长均匀的In_xGa_<1-x>As和In_xGa_<1-x>Sb三元体晶体和高质量的外延层，用于制造热光伏（TPV）能量转换系统。在这方面，进行了以下实验并进行了分析。在飞机和落塔实验中研究了微重力条件下In_xGa_<1-x>Sb晶体的结晶过程。结果表明，重力对固液界面形状和晶体成分分布有一定的影响。模拟结果表明，溶质自然对流和溶质马兰戈尼对流对晶体生长的影响非常显著。通过冷却源和种子晶体，在GaSb或InSb种子上生长出了均匀的In_xGa_<1-x>Sb体晶，其生长速率和温度梯度均可达到最优值。利用旋转Bridgman法在GaAs种子上生长出了更多x值高达0.12的x>As单晶。由于连续向In-Ga-As溶液中添加GaAs源材料，生长晶体的x值是均匀的。利用桥层生长技术成功地在图像化的III-V二元衬底上实现了高质量的In_xGa_<1-x>As外延层。为了制备高铟含量的In_xGa_<1-x>As脱膜，成功地采用了“成分转换”技术。高品质的脱毛剂中铟含量高达80%。在此基础上，详细研究了转化机制的起源。首次开发了在III-V衬底上生长具有低蚀坑密度的In_xGa_<1-x>Sb和In_xGa_<1-x>As锥体薄膜的两种选择性生长技术，即空心锥体外延技术和成分转换与空心锥体外延技术的结合。为了使锥体脱壳层用于光学器件的制备，本文详细研究了Te杂质对GaSb锥体脱壳层结构性质的影响。采用Zn扩散技术在n型GaSb衬底上生长了p型GaSb薄膜。在不同的退火条件下得到了涂层的组成曲线。少

The main objectives of the on going research are to develop new techniques to grow homogeneous In_xGa_<1-x>As and In_xGa_<1-x>Sb ternary bulk crystals and high quality epitaxial layers for the fabrication of Thermo-Photo-Voltaic (TPV) energy conversion system. In this aspect, the following experiments have been carried out and analyzed.1.The crystallization process of In_xGa_<1-x>Sb crystals has been investigated under microgravity in an airplane and a drop tower experiments. It is observed that the shape of solid-liquid interface and the composition profile of the crystals are influenced by gravity. Simulation results have shown that the effects of solutal natural convection and solutal Marangoni convection are very significant during the growth of the crystals.2.Homogeneous In_xGa_<1-x>Sb bulk crystals have been grown on GaSb or InSb seeds by cooling source and seed crystals at the optimized value estimated from the temperature gradient in the solution and the growth rate. In_xGa_<1- … More x>As single crystals with x values up to 0.12 were grown on GaAs seed by Rotational Bridgman method. The x values of the grown crystals are found to be homogeneous due to the feeding of GaAs source materials continuously into the In-Ga-As solution.3.Bridge layer growth technique has been successfully employed to realize high quality epitaxial layers of In_xGa_<1-x>As on patterned III-V binary substrates. For the growth of In_xGa_<1-x>As epilayers with high indium composition, a novel technique named as "composition conversion" has been successfully utilized. High quality epilayers have been grown with indium composition as high as 80%. Furthermore, the origins of the conversion mechanism have been studied in detail.4.Two selective growth techniques have been developed for the first time to grow In_xGa_<1-x>Sb and In_xGa_<1-x>As pyramidal epilayers with low etch pit density on III-V substrates viz., hollow pyramidal epitaxy technique, and the combination of composition conversion and hollow pyramidal epitaxy technique. In order to make use of the pyramidal epilayer for fabrication of optical devices, the effect of Te impurity on the structural properties of GaSb pyramidal epilayer has been studied in detail.5.p-type GaSb epilayers have been grown on n-type GaSb substrates by Zn diffusion technique. The composition profiles of the epilayers were obtained under various annealing conditions. Less