The Ga-Sb-S-H system was thermodynamically treated in order to estimate the maximum level of sulphur doping in GaSb single crystals grown by the Czochralski technique without encapsulant in a flowing atmosphere of hydrogen, the growth rate being 1.2 cm h-1. The calculated concentration of dissolved sulphur in GaSb solid was 1016-1017 atoms/cm3, which is in good agreement with the experimentally measured values of about 1017 atoms/cm3 in the GaSb single crystals. After exceeding approximately 1.5*1018 atoms/cm3 in the melt, the second phase (Ga2S) started to separate spontaneously in the melt; the single-crystalline growth was impaired and became either polycrystalline or twin-like.
The luminescence properties of In doped GaSb single crystals have been studied by the cathodoluminescence (CL) technique in the scanning electron microscope. It has been found that indium induces a certain reduction on the native acceptor concentration in contrast to what occurs with other isoelectronic dopants (e.g. aluminium). Large In concentrations lead to the formation of the ternary compound InxGa1-xSb as revealed by CL spectra and x-ray measurements. In particular, a luminescence band and x-ray diffraction peaks observed in highly doped samples are attributed to the presence of InxGa1-xSb.
The influence of the doping level on the radiative recombination properties of GaSb:Se crystals has been investigated by cathodoluminescence (CL) microscopy and spectroscopy in the scanning electron microscope. CL images evidence a high dislocation density and dopant segregation around the dislocation cores in highly-doped crystals. A progressive reduction of the Se content leads to a lower dislocation density and a more uniform luminescence spatial distribution. CL spectra reveal the existence of three Se-related emission bands, centred in all the samples investigated at about 765, 740 and 719 meV, whose relative intensity is influenced by the doping level. Measurements carried out at different temperatures and excitation densities indicate that these bands can be attributed to transitions from the conduction band to deep acceptor levels.
GaSb 1 µm-thick layers were grown by molecular beam epitaxy on GaAs (0 0 1). The effects of the growth conditions on the crystalline quality, surface morphology, electrical properties and optical properties were studied by double crystalline x-ray diffraction, atomic force microscopy, Hall measurement and photoluminescence spectroscopy, respectively. It was found that the surface roughness and hole mobility are highly dependent on the antimony-to-gallium flux ratios and growth temperatures. The crystalline quality, electrical properties and optical properties of GaSb layers were also studied as functions of growth rate, and it was found that a suitably low growth rate is beneficial for the crystalline quality and electrical and optical properties. Better crystal quality GaSb layers with a minimum root mean square surface roughness of 0.1 nm and good optical properties were obtained at a growth rate of 0.25 µm h−1.