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

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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 NT, the volume capture rate cn, the absolute photoionisation cross section sigma n, the effective radius of the centre rT*, the Huang-Rhys factor S, the Franck-Condon shift dFC, the optical ionisation energy ET and its dependence on temperature. They are NT=1.4*1014 cm-3, cn=1.3*10-8 cm3 s-1 at 100K, sigma n=7.1*10-18 cm2 at 100K and at 0.4682 eV, rT*=11 AA, S=3.5, dFC=0.11 eV, ET=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.