Mercury cadmium selenide for infrared detection

Samples of HgCdSe alloys were grown via molecular beam epitaxy on thick ZnTe buffer layers on Si substrates. Two Se sources were used: an effusion cell loaded with 5N source material that produced a predominantly Se6 beam and a cracker loaded with 6N material that could produce a predominantly Se2 beam. The background electron concentration in as-grown samples was significantly reduced by switching to the Se cracker source, going from 1017–1018 cm−3 to 3–5 × 1016 cm−3 at 12 K. The concentration remained low even when the cracking zone temperature was lowered to produce a predominantly Se6 beam, which strongly suggests that a major source of donor defects is impurities from the Se source material rather than Se species. Secondary ion mass spectroscopy was performed. Likely donors such as F, Br, and Cl were detected at the ZnTe interface while C, O, and Si were found at the interface and in the top 1.5 μm from the surface in all samples measured. The electron concentration for all samples increased when annealed in a Cd or Hg overpressure and decreased when annealed under Se. This suggests the presence of native defects such as vacancies and interstitials in addition to impurities. Overall, by switching to higher purity Se material and then annealing under Se overpressures, the background electron concentration was reduced by an order of magnitude, with the lowest value achieved being 9.4 × 1015 cm−3 at 12 K.