STRAINED LAYER EPITAXY OF INGAAS BY MBE AND MIGRATION ENHANCED EPITAXY - COMPARISON OF GROWTH MODES AND SURFACE QUALITY

Our measurements on a series of pseudomorphic n-type modulation doped field effect transistors have shown that the mobility of the two-dimensional carriers appears to suffer from increased interface roughness as the strain increases. Reflection high energy electron diffraction oscillation studies in In(x)Ga1-xAs grown by molecular beam epitaxy show that as the strain in the overlayer increases, the growth modes change from layer-by-layer to three-dimensional island growth. However, in migration enhanced epitaxy, we find that the growth remains in the layer-by-layer mode even for high strain. Reflection high energy electron diffraction oscillations also show that surface roughness in strained layers grown by molecular beam epitaxy can be smoothed by just a few monolayers grown by migration enhanced epitaxy. This suggests that for pseudomorphic devices most of the strained active layer might be grown by molecular beam epitaxy but just a few monolayers before interface formation by migration enhanced epitaxy to produce an abrupt interface. Our device results validate this observation.