Photoconductivity, electron traps and level-broadening in GaAs:O

The steady state and transient photoconductivity of n-type GaAs doped with oxygen (2 Omega cm at 300K) was measured between 90 and 150K as a function of the intensity of filtered (1-3 mu m) light. Besides two deep levels which provided photoexcited electrons, discrete levels at 0.23 eV (5*10 14 cm -3 ) and at 0.15 eV (3*10 14 cm -3 ) below the conduction band were found. The main discovery was of a complex of traps at 0.05 eV which exhibited level-broadening. The broadening could be shown to possess a Gaussian form, and to have a half-width of about 10 meV. The capture cross-section associated with the 0.05 eV complex was 1*10 -19 cm 2 at 100K rising with temperature, with an activation energy of 0.077 eV with about 10% error. Confirmation of shallow trapping with this temperature dependence was obtained from measurements of photoconductivity produced by a pulsed CO 2 -laser at 10.6 mu m. Rough values of the capture cross-sections for the other centres were also obtained.