Correlation between growth behavior, internal stress distribution and properties of ZnO:Zn crystals grown by carbon-assisted chemical vapor transport

Internal stress and stress-related defects are considered as the major obstacles that significantly hinder the growth of high-quality ZnO-based crystals. In this work, high-crystalline-quality ZnO:Zn bulk crystals were successfully grown by carbon-assisted chemical vapor transport (CVT). Internal stress in the crystal was directly measured by a neutron beam from a reactor, and stress distributions along the radial direction at different depths were obtained. The stress, temperature, and flow fields in the growth system were simulated by the finite element (FE) method, and the results agreed with the neutron stress analysis. The etch pit density (EPD), Hall properties, and optical transmittances of different crystal regions were studied in detail, and the distribution trend of the crystal properties was consistent with that of internal stress and stress-related defects in the crystal. It is found that the unique temperature filed in the growth system causes the crystal to bend to a slightly convex toward the growth direction and gives rise to a driving force for structural defect formation. The + c and -c faces of the crystal are subjected to tensile and compressive stress, respectively. The maximum stress values are about 280 MPa and -291 MPa near the central regions of +/- c faces, while the crystal periphery is basically free of internal stress. The region near the center of +c face has an EPD of 7.5 x 10(3) cm(-2) and a transmittance of 79.2% at 800 nm wavelength, while the corresponding carrier concentration and mobility are 2.27 x 10(17) cm(-3) and 159 cm(2)/V.s, respectively. By comparison, the crystal periphery has an EPD of 10(2) cm(-2) with an 80.5% transmittance at 800 nm, while the carrier concentration and mobility are 1.85 x 10(17) cm(-3) and 184 cm(2)/V.s, respectively.