MECHANISM OF LIGHT-INDUCED REACTIVATION OF ACCEPTORS IN P-TYPE HYDROGENATED GALLIUM-ARSENIDE

The mechanism of light-induced reactivation (LIR) of shallow substitutional acceptors in high-purity p-type hydrogenated GaAs has been investigated. Low-temperature photoluminescence was used to determine the dependence of the rate and extent of this effect on photon energy, illumination intensity, sample temperature, and chemical identity of the passivated acceptor impurities. The efficiency of LIR at T = 1.7 K increases sharply for photon energies greater than a threshold value of E(t) almost-equal-to E(g) - 7.5 +/- 0.5 meV, where E(g) is the band-gap energy of GaAs. This energy corresponds approximately to the onset of acceptor-bound exciton absorption in the material. For h-nu > E(t), the initial LIR rate depends on the square of the light intensity, indicating a bimolecular reaction involving the photogenerated carriers. For sufficiently large values of the product of the light intensity, and the illumination time, the LIR process saturates. Both the extent of the subthreshold effect for h-nu < E(t), and the saturation level that is attainable for h-nu > E(t) are independent of the photon energy, excitation power, and exposure time in the investigated ranges of these quantities. The LIR effect is practically athermal for very weakly neutralized acceptor species (e.g., Mg), but it is thermally assisted for Zn, Si, and Ge acceptors which form more stable complexes with hydrogen. From these results it is inferred, that the LIR of acceptors is electronically stimulated, possibly via a recombination-enhanced vibrational excitation of the acceptor-hydrogen complexes. A kinetic model of the LIR process, which accounts for the experimental results by assuming a reverse reaction of electronically stimulated relaxation of hydrogen toward an acceptor (light-induced passivation), is proposed.