FUNDAMENTAL ISSUES OF DEVICE-RELEVANT LOW-TEMPERATURE GAAS AND RELATED MATERIALS PROPERTIES

In the past few years, a flurry of activity has been devoted to the st udies and device applications of non-stoichiometric GaAs grown by mole cular beam epitaxy at the extremely low temperature (LT) of 250 degree s C or below using, in essence, identical growth conditions to those o f 'normal'. high temperature (> 500 degrees C) grown materials. These materials are highly non-stoichiometric, containing a massive amount o f excess As in the lattice which totally dominates the electro-optical characteristics. This essentially defect-controlled material, in both its as-grown state and after annealing, leads thereafter to a number of device concepts and applications ranging from buffer layers to fast photoconductors. In this study, a detailed investigation of the growt h conditions, including growth dynamics, has established that the non- stoichiometry of LT GaAs is not an intrinsic property but a perfectly controllable one. We report here on new phenomena associated with the growth of GaAs and related compounds at less than or equal to 250 degr ees C and present data on highly electrically and optically active mat erial demonstrating electro-optical qualities comparable to those grow n at high temperatures, as evidenced by photoluminescence (PL) of quan tum wells and sheet densities and mobilities in HEMT structures. It is therefore surmised that non-stoichiometry in low-temperature-grown Ga As can be overcome, leading to the growth of stoichiometric low temper ature (SLT) materials possessing properties similar to those of conven tional, high-temperature-grown layers. (C) 1997 Elsevier Science S.A.