Absorption spectra of Ti-doped GaAs

We observed the 3d¹ intracenter transition ²²{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 Ti³⁺(3d¹) 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 Ti²⁺(3d²) intracenter transitions at 0.66 and 1.01 eV. The corresponding single acceptor level Ti³⁺/Ti²⁺ was identified to be at 0.23±{}0.01 eV below the conduction band on the basis of deep-level transient spectroscopy and capacitance transient measurements.