Infrared Spectroscopy of Light Impurities in GaSb

In our work we study the doping behaviour of sulphur in Czochralski grown GaSb by means of the high resolution Fourier transform infrared spectroscopy and the secondary ion mass spectroscopy. We have revealed that the sulphur impurity forms an effective mass like donor state bound to the L-minimum of the conduction band. From the far infrared spectrum of this donor we derive the effective band masses of the L band minimum. We also observe local vibrational modes related to the arsenic and phosphorus isoelectronic impurities. From the nearest neighbour isotope splittings of these modes we conclude that the arsenic impurity occupies a tetrahedral substitutional site and the phosphorus impurity — a low symmetry lattice site.