Photoconductivity in n-type GaAs:O associated with the deep level at 0.4 eV

Abstract

The photoconductivity of GaAs:O (2 Omega cm at 300K) has been studied between 90-200K using a pulsed HF gas laser, in addition to conventional steady-state and chopped-light techniques. The substantial power available has been exploited to study photoresponse up to saturation level. Besides confirming the existence of a broadened trap distribution of width 160 meV below the conduction band, the authors have determined for the 0.4 eV centre the density N_T, the volume capture rate c_n, the absolute photoionisation cross section sigma _n, the effective radius of the centre r_T*, the Huang-Rhys factor S, the Franck-Condon shift d_FC, the optical ionisation energy E_T and its dependence on temperature. They are N_T=1.4*10¹⁴ cm^-3, c_n=1.3*10^-8 cm³ s^-1 at 100K, sigma _n=7.1*10^-18 cm² at 100K and at 0.4682 eV, r_T*=11 AA, S=3.5, d_FC=0.11 eV, E_T=0.420-7*10^-5 TeV. The spectral dependence of sigma _n agrees with a new model by Ridley (1980) rather than with the Lucovsky model, and this new model is exploited in the derivation of the above quantities. It is pointed out that the Franck-Condon shift may be more a property of the host crystal than of the defect.