Surface Studies at Atmospheric Pressure and Under UHV Conditions During Growth of GaAs

Abstract

A fundamental step in OMVPE growth of GaAs on GaAs (100) is the decomposition of an organometallic reagent such as trimethyl gallium (TMG) or triethyl gallium (TEG) on or above a GaAs (100) substrate which is believed to be clean, atomically smooth and As-rich. The absence of significant levels of carbon incorporation is somewhat surprising to a surface chemist since if reactive species such as ethyl or methyl radicals are produced either on the substrate surface or in the gas-phase via pyrolysis of the organometallic, then chemical intuition suggests that some carbon incorporation must occur. Thus it is necessary to invoke specific surface processes capable of removing carbon containing species at a rate considerably higher than the growth rate or assume that alternative decomposition pathways are available for the organometallic. At typical growth temperatures employed in QMVPE growth of GaAs (≈ 600°C) it is highly likely that some gas-phase pyrolysis of the organometallic occurs. Yet recent studies by Stringfellow and co-workers suggest that for the growth of GaAs from TMG and AsH3, the decomposition product is mainly CH4 and forms via addition of hydrogen resulting from the decomposition of AsH3 i.e. the H2 carrier gas is not involved in the decomposition of the organometallic. Thus it is concluded that the average gas-phase free radical concentration is very small.