Correlations of photoluminescence with defect densities in semi-insulating gallium arsenide

Room-temperature luminescence response to a Kr-Ar laser has been used to obtain two-dimensional dislocation maps of LEC GaAs wafers by rastering the laser beam across a wafer surface and storing the response in a computer for subsequent display. One-dimensional line scans of photoluminescence can also be made and indicate a high degree of correlation with the dislocation density. Epitaxial layers, however, show almost no correlation between PL and dislocations and are much "brighter" than bulk-grown material, while Cr-doped HB wafers show only a slight correlation and are much "dimmer" than LEC material. A degradation of luminescence with time is observed when the laser beam is maintained on a single spot, and this decrease is faster as the incident power is increased. Surface recombination, nonradiative recombination, and refractive index variations have been investigated to explain the PL behavior and the result is that non-radiative recombination (or radiative recombination at energies less than I.1 eV) is dominant, and that the effect of dislocations in LEC material is to getter nonradiative recombination centers.