Ion implantation of boron in germanium

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Abstract
The activation of boron implanted at room temperature into germanium has been studied. In sharp contrast to all other group III elements boron forms a p-type layer before any postimplant annealing steps. Variable temperature Hall effect measurements and deep level transient spectroscopy experiments indicate that all of the boron ions are electrically active as shallow acceptor centers over the entire dose range (5×1011/cm2 to 1×1014/cm2) and energy range (25–100 keV) investigated, without any postimplant annealing. The concentration of damage related acceptor centers is only 10% of the boron related, shallow accepted centers concentration for low-energy implants (25 keV), but becomes dominant at high energies (100 keV) and low doses (<1×1012/cm2). Three damage related hole traps are produced by ion implantation of 11B+. Two of these hole traps have also been observed in γ-irradiated Ge and may be oxygen-vacancy related defects, while the third trap may be divacancy related. All three traps anneal out at low temperatures (<300 °C). Room-temperature implantation of BF+2 into Ge, does not lead to substitutionally active boron without annealing. A thermal cycle of 350 °C for 30 min activates 100% of the boron.