Cathodoluminescence study of In_xGa_1-xSb crystals grown by the Bridgman method

The nature and the spatial distribution of radiative defects in In _xGa_1-xSb grown by the vertical Bridgman method have been studied by cathodoluminescence (CL) in a scanning electron microscope. The CL results have been complemented by X-ray microanalysis and backscattered electron imaging to relate the local luminescence properties to the chemical composition. Measurements of the band-gap energy from the CL spectra, supported by X-ray compositional mappings, reveal an effective incorporation of In in the matrix, leading to the formation of the ternary alloy in the whole volume of the ingot. A low gradient of the In content along the growth axis has been found. The CL spectra of the ternary alloy exhibit similar general features to those reported for GaSb. An observed red shift of the near band edge luminescence in In_xGa_1-xSb, relative to that of GaSb, is due to the reduction in the band gap with increasing x. A band often observed in the CL spectra, peaked at about 20meV below the band-gap energy, is attributed to the presence in the ternary alloy of an acceptor level that would correspond to the V_Ga-Ga_Sb acceptor in GaSb.