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

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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.