It is shown that Li diffusion of GaAs can give rise to semi-insulating samples with electrical resistivity as high as ${10}^7$ Ω cm in undoped, n-type, and p-type starting materials. The optical properties of the compensated samples are correlated with the depletion of free carriers caused by the Li diffusion. The radiative recombination of the Li-compensated samples is dominated by emissions with excitation-dependent peak positions that shift to lower energies with increasing compensation. The photoluminescence properties are characteristic of fluctuations of the electrostatic potential in strongly doped, compensated crystals.

• Received 26 August 1992

DOI:https://doi.org/10.1103/PhysRevB.47.9418