Role of stoichiometry in low temperature grown GaAs for MESFET structures

In the past few years a flurry of activity has been devoted to the studies and device application of non-stoichiometric GaAs grown by the technique of Molecular Beam Epitaxy at the extremely low temperatures (LT) of 250 °C or below using in essence identical growth conditions to those of `normal', high temperature (>500 °C) grown materials. The material thus grown is highly non-stoichiometric with a massive incorporation of excess As in the lattice which then totally dominates the electrical and optical characteristics of the material. In the present studies, a detailed investigation of the growth conditions including growth dynamics has established that the non-stoichiometry of LT GaAs is not an intrinsic property but a perfectly controllable one leading to the possibility of growth of Stoichiometric Low temperature (SLT) GaAs. Epitaxial layers of both LT and SLT GaAs layers were grown and assessed as to their suitability as buffer layers in conventional MESFET structures. Both the mobility and charge density in the channel are shown to be strongly affected by the underlying buffer layer. Because of the control afforded in the growth of this structure using stoichiometric beams, a MESFET structure was entirely grown at the low growth temperature of 350 °C and yet still retained high electrical and optical properties.