Implant isolation of Zn-doped GaAs epilayers: effects of ion species, doping concentration, and implantation temperature

Abstract

The electrical isolation of Zn-doped GaAs layers grown by metalorganic chemical vapor deposition was studied using H, Li, C, and O ion implantation. The ion mass did not play a significant role in the stability of isolation, and a similar activation energy of ∼(0.63±0.03 eV) was obtained for isolation using either H or O ions. Furthermore, the isolation was stable against isochronal annealing up to 550 °C as long as the ion dose was 2–3.5 times the threshold dose for complete isolation, Dth, for the respective ion species. By studying the thermal stability and the temperature dependence of isolation, we have demonstrated the various stages leading to the production of stable isolation with the increasing dose of 2 MeV C ions. For ion doses less than 0.5Dth,point defects which are stable below 250 °C are responsible for the degradation of hole mobility and hole trapping. The stability of isolation is increased to ∼400 °C for a dose Dth due to the creation of defect pairs. Furthermore, the hopping conduction mechanism is already present in the damaged epilayer implanted to Dth. Higher order defect clusters or complexes, such as the arsenic antisite, AsGa, are responsible for the thermal stability of implantation isolation at 550 °C. The substrate temperature (−196–200 °C) does not have an effect on the isolation process further revealing that the stability of isolation is related to defect clusters and not point-like defects. An average number of eight carbon ions with energy of 2 MeV are required to compensate 100 holes, which provides a general guideline for choosing the ion dose required for the isolation of a GaAs layer doped with a known Zn concentration. A discussion of the results on the implantation isolation of p-GaAs previously reported in the literature is also included.