Research Initiation Award: Chemical Kinetics and Transport Phenomena of GaAs Growth by MOCVD Using Alternative Arsenic Precursors

金属有机化学气相沉积（MOCVD）是一种通用技术，用于沉积微电子制造材料，包括金属，半导体和绝缘体，使用各种有机金属前体。在典型的热解MOCVD工艺中，将反应气体的混合物注入加热的固体衬底并沉积薄的固体薄膜。MOCVD是制备III-V和iv类化合物半导体（如GaAs、AlGaAs、InP、InGaAs、InGaAsP、ZnSe、HgCdTe等）薄外延层和异质结构的一种很有前途的技术。目前限制MOCVD用于生长化合物半导体薄膜和人工微结构（超晶格、量子阱、原子突变组成和掺杂界面）的商业应用的问题是：(1)缺乏对潜在气相和表面反应的理解；(2)缺乏对化学动力学和决定材料生长和组成均匀性的复杂传输现象之间耦合的理解；(3)常用前驱气体的高毒性引起的安全问题；特别是v族氢化物砷和膦。本研究的目的是：(a)研究在GaAs和AlxGa1-xAs MOCVD中使用的替代（更安全的）砷前体（三甲基-胂，叔丁基-胂）和常见的有机金属前体（三甲基-和三乙基-镓和铝）的分解动力学；(b)开发可替代砷前体的砷化镓生长的反应-运输模型，能够预测观察到的生长和碳掺入率；(c)利用上述前驱体生长GaAs外延层并研究其性能。前驱体的分解将在逆流扩散反应器中进行，以获得纯均匀的反应速率，并在热壁管式反应器中进行，以获得总速率。本研究的最终目标是开发有效扩大MOCVD工艺的程序，以便从更安全的前驱体气体中沉积GaAs的薄外延层，并控制均匀性，成分和形貌。

Metalorganic chemical vapor deposition (MOCVD) is a versatile technique for depositing materials for microelectronics fabrication, including metals, semiconductors, and insulators, using a variety of organometallic precursors. In a typical pyrolytic MOCVD process, a mixture of reactive gases is injected over a heated solid substrate and a thin solid film is deposited. MOCVD is a promising technique for depositing thin epitaxial layers and heterostructures of III-V and IIV compound semi-conductors such as GaAs, AlGaAs, InP, InGaAs, InGaAsP, ZnSe, HgCdTe, etc. The problems that are currently limiting commercial applications of MOCVD for growing thin films of compound semi-conductors and artificial microstructures (superlattices, quantum wells, and atomically abrupt compositional and doping interfaces) are:(1) lack of understanding of the underlying gas-phase and surface reactions, (2) lack of understanding of the coupling between chemical kinetics and complex transport phenomena that determines the growth and compositional uniformity of the material, and (3) safety issues arising from the high toxicity of commonly used precursor gases, especially of the group-V hydrides arsine and phosphine. The objectives of this research is: (a) to study the decomposition kinetics of alternative (safer) arsenic precursors (trimethyl-arsine, tertiary-butyl-arsine) and common organo-metallic precursors (trimethyl- and triethyl- gallium and aluminum) used in MOCVD of GaAs and AlxGa1-xAs; (b) to develop reaction-transport models of GaAs growth from alternative arsenic precursors capable of predicting observed growth and carbon incorporation rates; (c) to grow GaAs epitaxial layers from the above precursors and study their properties. The decomposition of the precursors will be performed in a counterflow diffusion reactor to obtain purely homogeneous reaction rates and in a hot-wall tubular reactor to obtain overall rates. The ultimate goal of this research is to develop procedures for efficient scale-up of the MOCVD process for depositing thin epitaxial layers of GaAs from safer precursor gases and with controlled uniformity, composition, and morphology.