A new MOVPE reactor for heteroepitaxial GaAs deposition on large-scale Ge substrates

Abstract

Feasibility of manufacturing a new metalorganic vapor phase epitaxy (MOVPE) reactor for heteroepitaxial GaAs deposition on large-scale Ge substrates for the production of satellite-use solar cells was investigated. The overall deposition mechanism for GaAs growth from trimethylgallium (TMG) and AsH 3 was fully checked and revised through quantum chemistry calculations. Then, the resulting chemical kinetic scheme was used to perform 2D and 3D simulations of the reactor chamber, predicting the GaAs growth rate profile over the whole substrate. Several simulations were performed to optimize reactor shape and geometry to enlarge the so-called “flat area”. The chosen reactor geometry, with the goal of avoiding the formation of parasitic flows and back-mixings, was that of a cold wall horizontal reactor, with rotating susceptor and round-shaped outer walls, and with a single jet gas inlet apparatus. The reactor was assembled at IMEM-CNR laboratory (Parma, Italy): it is completely home made and responds to the requirement of a research and development (R and D) process in a research institute, since it is less expensive than commercially available MOVPE reactors; it is modular and expandable as new reagents lines will become necessary for the growth of III–V arsenides and phosphides; it uses a custom made control software developed on a programmable logic computer (PLC). Moreover, it integrates some new technology such as digital-controlled mass flow controllers and pressure controller and a low-consume vent line with a retroactive pressure control. Some tests were made and GaAs on Ge was successfully deposited.