Epitaxial growth from organometallic sources in high vacuum

Abstract

Herein we describe a process that combines some of the principal advantages of molecular beam epitaxy and metal-organic chemical vapor deposition (MOCVD) systems. We call this process vacuum chemical epitaxy (VCE). In this process, multiple group III-alkyl molecular beams are directed through a water-cooled gas distribution block onto wafers providing for the growth of uniform films over large areas with high group III-alkyl utilization efficiency. The group V source, on the other hand, is injected at a single point on one side of the deposition zone. The group V molecules are confined and undergo molecular flow across the deposition zone. The utilization efficiency of the group V source material can be enhanced by the use of a thermal cracker at the point of group V gas injection. This high group V gas utilization efficiency, combined with the fact that all of the reactants are contained within a stainless-steel vacuum chamber equipped with an air lock for wafer loading, leads to a safer MOCVD scaleup reactor. In this paper our VCE reactor is described in some detail along with the properties of III–V films grown with this equipment. The fabrication of a GaAsSb solar cell with an active area energy conversion efficiency of 26.7% demonstrates that VCE has the capability of producing high-performance devices.