We demonstrate that x-ray irradiation can be used to induce an insulator-me
tal transition in Si-doped Al0.35Ga0.65As, a semiconductor with DX centers.
The excitation mechanism of the DX centers into their shallow donor state
was revealed by studying the photoconductance along with fluorescence. The
photoconductance as a function of incident x-ray energy exhibits an edge bo
th at the Ga and As K edge, implying that core-hole excitation of Ga and As
are efficient primary steps for the excitation of DX centers. A high quant
um yield (>1) suggests that the excitation is indirect and nonlocal, due to
secondary electrons, holes, and fluorescence photons. (C) 2001 American In
stitute of Physics.