Identification of a defect in a semiconductor:EL2 in GaAs

We present here a complete set of experimental results, obtained by electron paramagnetic resonance (EPR) and deep-level transient spectroscopy (DLTS), on the so-called EL2 defect in GaAs. It is obtained on semi-insulating materials and specially doped materials grown as semi-insulating ones, which have been submitted to electron irradiation, thermal treatments, and annealing followed by a quench. First, we show that there are two types of defects which give rise to the same EPR spectrum associated with the antisite ${\mathrm{As}}_{\mathrm{Ga}}$: the one associated with EL2, since it presents its well-characterized metastable property, and another one associated with the isolated ${\mathrm{As}}_{\mathrm{Ga}}$, which is not metastable. Second, we demonstrate that an EL2 defect can be transformed into an isolated ${\mathrm{As}}_{\mathrm{Ga}}$ by a thermal treatment. Third, we describe how EL2 defects can be regenerated by a low-temperature treatment in materials which have been annealed and quenched. These results, together with considerations on self-diffusion in GaAs, allow us to conclude that EL2 is a complex formed by an isolated ${\mathrm{As}}_{\mathrm{Ga}}$ and an intrinsic interstitial defect, namely ${\mathrm{As}}_{\mathrm{i}}$ or ${\mathrm{Ga}}_{\mathrm{i}}$. Finally, we studied the kinetics of EL2 regeneration by DLTS in quenched material; since this regeneration occurs through the interstitial mobility and since the associated activation energy is similar to the one found for ${\mathrm{As}}_{\mathrm{i}}$ mobility in electron irradiated p-type material, we deduce that EL2 is the complex ${\mathrm{As}}_{\mathrm{Ga}+{\mathrm{As}}_{\mathrm{i}}}$. All these results, as well as the ones provided by the literature, can be understood if the stable state of EL2 corresponds to ${\mathrm{As}}_{\mathrm{i}}$ in second-neighbor position of ${\mathrm{As}}_{\mathrm{Ga}}$ while the metastable state corresponds to ${\mathrm{As}}_{\mathrm{i}}$ in first-neighbor position.