Electrical and optical properties of Cu- and Ga-doped Hg _1-xCd_xTe layers grown by liquid-phase epitaxy

The influence of Cu (acceptor) and Ga (donor) on the electrical and optical properties of Hg_1-xCd_xTe (x=0.2) layers was investigated. The layers were grown by liquid-phase epitaxy from Te-rich solutions and the dopants were intentionally introduced during the growth process. Doping efficiencies between 0.025 at a hole concentration of p=6×10 ¹⁸ cm^-3 and 0.15 at p=6×10¹⁷ cm^-3 were found for Cu. The electron concentration in the as-grown Ga-doped layers saturated at n=2×10¹⁷ cm^-3, but increased significantly to n=8×10¹⁸ cm^-3 as a result of an annealing process. The doping efficiency was 0.02. The doping and electrical properties of the layers are explained by assuming incorporation of both electrically active and electrically inactive impurity atoms. The high free electron concentrations in the Ga-doped layers resulted in a strong Burstein-Moss shift [T. S. Moss, G. J. Burrell, and B. Ellis, in Semiconductor Optoelectronics (Butterworths, London, 1973), p. 42] of the absorption edge, and effects of plasma frequency. These effects are analyzed and discussed.