Identification of a defect in a semiconductor:<i>EL</i>2 in GaAs

TLDR

EL2 defects arise in semi‑insulating GaAs that have undergone electron irradiation, thermal treatments, annealing, and quenching. The study presents comprehensive EPR and DLTS experimental results on the EL2 defect in GaAs. The authors used electron paramagnetic resonance and deep‑level transient spectroscopy to investigate the EL2 defect. The study demonstrates that EL2 is a complex of an isolated As_Ga antisite with an interstitial (As_i or Ga_i), that two defect types produce the same EPR spectrum but only the EL2 complex is metastable, that EL2 can be converted to isolated As_Ga by thermal treatment and regenerated by low‑temperature treatment, and that its regeneration kinetics involve As_i mobility with activation energy matching that of As_i in irradiated p‑type material, implying the stable state has As_i in a second‑neighbor position and the metastable state in a first‑neighbor position.

Abstract

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.