A growth method to obtain flat and relaxed In0.2Ga0.8As on GaAs (001) developed through in situ monitoring of surface topography and stress evolution

Abstract

In this paper we develop a growth process for obtaining flat and relaxed In 0.2 Ga 0.8 As layers on GaAs (001). The process designed is based on the results obtained by in situ and real time characterization of surface morphology and layer relaxation. In particular our results show that for growth temperatures T s ≤ 200 ºC, the relaxation of In 0.2 Ga 0.8 As layers is inhibited and the morphology does not evolve to a crosshatched pattern. After growth thermal treatments of these low temperature (LT) In 0.2 Ga 0.8 As layers induce the development of a very faint (rms = 0.5 nm) crosshatched-like morphology. The relaxation process during the thermal annealing is strongly asymmetric and the layers present a high final strain state. By growing on top of the LT layer another In 0.2 Ga 0.8 As layer at higher temperature, relaxation is increased up to R ≈ 70% and becomes symmetric. Depending on the growth process of the top layers morphology evolution differs, resulting better morphologies for top layers grown by atomic layer molecular beam epitaxy (ALMBE) at T s = 400 ºC. We have obtained 400 nm In 0.2 Ga 0.8 As layers with a final degree of relaxation R = 70% and very flat surfaces (rms = 0.9 nm).