Compensation mechanisms related to boron implantation in GaAs

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Abstract
Two different compensation mechanisms are shown to be responsible for the carrier removal observed after boron implantation in n-type GaAs: (i) Compensation due to complex lattice defects corresponding to implantation damage and which mainly give rise to two narrow bands in the band gap centered at Ec−0.55 eV and Ev+0.70 eV. These defects and the related compensation vanish after annealing for half an hour at temperatures between 350 and 550 °C by exodiffusion. (ii) Compensation due to chemical effects which consists in the formation of complexes between impurities already present in the wafer and the created defects or the boron atoms themselves. These complexes, which are not observed to exodiffuse, are stable at much higher temperatures, up to around 800 °C. It is shown that these complexes do not generate deep levels. Furthermore, it is established that a boron implantation at relatively high dose (1014 at cm−2) followed by an annealing at 860 °C, leads to a depletion of both the electrically active Cr atoms and the deep donor defect EL2 in the implanted region. The presence of boron does not seem to affect the electrical properties of implanted layers further annealed at 860 °C, as far as its concentration does not exceed 1–2×1017 cm−3. But larger concentrations, sometimes noticed in liquid-encapsulated Czochralski (LEC) semi-insulating substrates, might have a real influence.