Growth and characterization of substrate-quality ZnSe single crystals using seeded physical vapor transport

Crystallographic and optical characterization techniques were carried out on ZnSe single-crystal samples grown by the seeded physical vapor transport (SPVT) and by high-pressure Bridgman techniques. A comparison of etch pit densities shows much lower values for the SPVT material. The distribution of etch pits across a wafer is uniform in SPVT samples but extremely nonuniform in the Bridgman samples. X-ray topography studies reveal that the SPVT material has few defects and no grain boundaries while the Bridgman material shows both low and high angle grain boundaries. Photoluminescence (PL) data at 12 K on the SPVT material reveal an absence of donor acceptor pair (DAP) emissions. The spectrum is dominated by the I^d₁ Cu-related line and its phonon replicas and only weak Cu_g and Cu_r emissions are observed. No thermoluminescence (TL) is seen from the SPVT samples but they do give thermally stimulated conductivity (TSC) signals due to the release of holes from Cu_Zn centers with activation energies of 0.33 eV and 0.71 eV. Only hole states are seen in the SPVT material. In contrast the Bridgman samples show intense DAP PL lines, as well as I^d₁ lines. They show Cu_g and Cu_r emission, give strong TL and TSC signals, and reveal an array of both electron and hole states.