Molecular beam epitaxial growth of GaAs on CaF2/Si(111) substrate

Abstract

In this work, molecular beam epitaxial (MBE) growth of GaAs on CaF2/Si(111) substrates has been studied with both Rutherford backscattering spectroscopy and transmission electron microscopy. It has been observed that, under certain conditions, a chemical reaction between As adatoms and CaF2 layers can be induced, by which a more stable As layer on the CaF2 surface is formed. The existence of the As layer improves the Ga wettability on the CaF2 surface and, if properly controlled, leads to two-dimensional (2D) nucleation of GaAs on the CaF2/Si(111) surface as opposed to the more commonly observed three-dimensional growth. In subsequent growth, two kinds of twins have been observed. All samples were observed to have microtwins near the GaAs/CaF2 interface. These twins can be suppressed during the first 1000 Å, if the layer is grown in a narrow optimal growth window. Otherwise, the growth will be in a 3D mode at lower temperature, or, it will suffer from the formation of big rotational twins at higher temperature. It has been observed that growth on the vicinal substrates tilted to [1̄1̄2] azimuth is helpful in suppressing the development of rotational twins so that growth on these substrates have a wider optimal growth window.