Growth of GaP and AlGaP on GaP(1 1 1)B using gas-source molecular-beam-epitaxy

Abstract

We present an initial study of the influence of the growth parameters on the surface morphology and on the interface quality of homoepitaxial GaP(111) and heteroepitaxial GaP/AlGaP(111) grown on GaP(111)B substrates using Gas-Source Molecular Beam Epitaxy (GSMBE). Three different surface reconstructions are identified in the RHEED patterns during the growth runs. The Root Mean Square (RMS) surface roughness measured post-growth by AFM ranges from 3 to 10nm over 10×10µm2 areas, for a film thickness of 100–600nm. The results of 2θ-ω XRD scans on (111) and (311) planes reveal a stacking disorder in the AlGaP layer and further XRD phi-scan measurements on GaP (311) show strong peaks with 3-fold rotational symmetry and additional of 3-fold weak peaks indicating only a negligible fraction of the twinned crystal orientation in the substrate. TEM images of these samples show a smooth interface between the AlGaP layer and GaP substrate, and reveal the presence of a high density of extended defects such as stacking faults, twinning and dislocations lines in AlGaP layer whereas the GaP layer appears as pure Zinc-Blende. Further TEM analysis reveals composition and local strain variations for GaP/AlGaP samples associated with an undulated surface.