Metal–organic chemical vapor deposition of mercury cadmium telluride epitaxial films

Abstract

The interdiffused multilayer process (IMP) has been implemented on a computer controlled metal–organic chemical vapor deposition (MOCVD) system to improve the compositional uniformity of epitaxial films grown by this technique. Currently, this process is giving compositional uniformity of ≂3% over 1 cm2 on CdTe substrates. Full temperature Hall measurements have been performed to show that as-grown mercury cadmium telluride (MCT) (x∼0.2 and 0.3 epilayers have consistent p-type conductivity with carrier levels in the range of 2.5×1016 cm−3 to 1.7×1017 cm−3 at 77 K. For MCT with composition in the range x=0.2 to 0.3, the acceptor levels increased as an alkyl source was exhausted, but improved when a new source was introduced. The as-grown MCT layers have mobilities typically of 350 cm2 V−1 s−1 at 77 K, consistent with p-type material, and the mobility shows a high degree of reproducibility. Preliminary mercury annealing experiments to identify residual impurity levels were performed. A 15 μm MOCVD layer of composition x=0.19 on a CdTe substrate was isothermally annealed at 250 °C and gave an extrinsic carrier density of 2.2×1014 cm−3 and a mobility of 4.9×105 cm2 V−1 s−1 measured at 9 K. As a consequence of the layer’s composition and low extrinsic properties, the extrinsic level was not reached at 77 K and a donor level of 6.0×1014 cm−3 and a mobility of 3.2×105 cm2 V−1 s−1 were found.