Absorption spectra of Ti-doped GaAs.

Abstract

We observed the 3${d}^{1}$ intracenter transition $^{2}\mathrm{}^{2}$${\mathrm{T}}_{2}$ in semiconductor crystals having a tetrahedral crystal field. This absorption was measured in Ti-doped melt-grown GaAs crystals. The spectrum consists of two sharp zero-phonon lines at 0.566 and 0.569 eV and of some broad phonon features with a maximum at 0.64 eV. The ${\mathrm{Ti}}^{3+}$(3${\mathrm{d}}^{1}$) spectrum can only be observed in high-resistivity GaAs crystals. In n-type conducting crystals the compensation of titanium acceptors leads to the appearance of the ${\mathrm{Ti}}^{2+}$(3${\mathrm{d}}^{2}$) intracenter transitions at 0.66 and 1.01 eV. The corresponding single acceptor level ${\mathrm{Ti}}^{3+}$/${\mathrm{Ti}}^{2+}$ was identified to be at 0.23\ifmmode\pm\else\textpm\fi{}0.01 eV below the conduction band on the basis of deep-level transient spectroscopy and capacitance transient measurements.