Thermal annealing studies on boron-implanted HgCdTe diodes

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Abstract
Junction profiles of B+-implanted Hg1−xCdxTe are examined using reverse bias capacitance–voltage measurements. All devices are fabricated on residual copper-doped, low vacancy concentration, p-type bulk material with a net doping of 1.5×1015 cm−3. The junction profiles showed the as-implanted junctions to be abrupt with one side of the junction doped in the low- to mid-1014 cm−3 range. These data and related circumstantial evidence are consistent with an n−/p junction after implantation. Type conversion in the immediate vicinity of the junction is postulated to result from indiffusion of interstitial Hg that is created by implant damage, the annihilation of group-II site vacancies by the Hg, and the associated movement of the highly mobile copper acceptor away from the low vacancy concentration region via an interstitial gettering mechanism. An immobile background donor concentration produces the n− region in the copper denuded region. During thermal anneal treatments, grading of the junction and improvement of the reverse-recovery lifetime was observed. The junction grading due to some anneals accounts for the markedly lower tunnel-limited leakage currents. Secondary ion mass spectrometry profiles show no movement of the boron away from the implant region. With previous information showing the damage region to be n+, it is concluded that the overall structure of the as-implanted and annealed junctions is n+/n−/p with the important junction properties determined by the n−/p region.

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