Growth and properties of n- and p-type ZnO

We will focus our attention on growth and properties of low-resistivity, n-type ZnO single crystals (/spl mu//sub e/ /spl sim/ 230 cm/sup 2//V-s, n/sub e/ /spl sim/ 1 /spl times/ 10/sup 17//cm/sup 3/, at RT), including study and identification of their characteristic shallow residual donors that are thought to control the high electrical conductivity observed in as-grown, n-type ZnO crystals. We will also direct some of our attention to study of the electrical and optical properties of recently demonstrated, nitrogen-doped, homoepitaxial p-type ZnO films grown by molecular beam epitaxy (MBE), either on low-resistivity (/spl rho/) substrates, or on Li-diffused, semi-insulating ZnO substrates. Hall mobilities, carrier concentrations and resistivities of the p-type ZnO films ranged from /spl mu//sub p/ = 1-2 cm/sup 2//V-s, n/sub p/ = 9 /spl times/ 10/sup 16//cm/sup 3/ to 1-5 /spl times/ 10/sup 18//cm/sup 3/, and /spl rho/ /spl sim/ 10-40 ohm-cm, respectively. SIMS profiles have shown that the p-type films, with thickness typically in the range of 1-2 /spl mu/m, contained large concentrations of N-atoms (as high as 1 /spl times/ 10/sup 19//cm/sup 3/ in the films) against a background of N in the substrates /spl sim/ 1 /spl times/ 10/sup 17//cm/sup 3/, and temperature-dependent Hall measurements of activation energies have shown that the binding energy (BE) of N-acceptors in ZnO is -146 meV, comparable to the BE of shallow Mg acceptors in GaN (/spl sim/ 165 meV); conductivity measurements have shown that at least one of our p-type films is prone to instability and type conversion at cryogenic temperatures and under illumination with room light. MBE growth conditions necessary to achieve p-type ZnO:N films/ZnO are discussed together with the characteristic bandedge photoluminescence (PL) signatures of the p-type layers.