Electron-irradiation defects in $n$-type GaAs

We have studied the production and annealing of defects produced by 1-MeV electron irradiation of $n$-type GaAs. Two of these defects lie at 0.15 and 0.31 eV from the conduction band, respectively; in addition, there is at least one acceptor much closer to the valence band. The carrier-removal rate depends upon sample purity but is independent of the irradiation flux. The removal rate is also highly dependent upon the position of the the Fermi level, an effect which is considered in some detail. At about 200°C, the defects recover in two stages, with the respective recovery rates given by ${\lambda }_1\simeq 3\times {10}^8\exp (-\frac{1.2}{\mathrm{kT}})$ and ${\lambda }_2\simeq 1\times {10}^{12}\exp (-\frac{1.6}{\mathrm{kT}})$ where the energies are in eV; ${\lambda }_2$ is somewhat dependent upon sample purity. In the highest-purity samples a reverse recovery phenomenon sometimes occurs, on about the same scale as ${\lambda }_1$. We present models for the production and recovery which are consistent with most of these results, as well as with other data found in the literature. It is suggested that the activation energies found in ${\lambda }_1$ and ${\lambda }_2$ may well be dissociation energies, rather than motional energies. Although the observed defects cannot be specifically identified, it appears that the level at 0.31 eV is a donor, and that at 0.15 eV is an acceptor; however, these conclusions are not firm.