Electrical and optical properties of as-grown and electron-irradiated ZnO

Large-diameter (up to 3-inch), n-type ZnO boules grown by a new vapor-phase transport method were studied by temperature-dependent Hall-effect (TDH) and photoluminescence (PL) measurements. From fits to the TDH data, the dominant donor has a concentration N_D of about 1×10¹⁷ cm^-3 and an energy of about 60 meV, close to the expected hydrogenic value, whereas the total acceptor concentration N_A is much lower, about 2×10¹⁵ cm^-3. The 2-K PL data include a series of at least seven sharp lines over the energy range 3.356-3.366 eV, and from polarization, magnetic-field, and annealing (up to 1000°C) experiments, these lines are interpreted as donor-bound excitons associated with donor complexes having different spacings between the atomic species. Electron-irradiation experiments show an electrical and optical threshold, attributed to Zn displacements, at an electron bombardment energy of about 1.3 MeV. The irradiation creates acceptors and destroys shallow donors, but these effects are produced at much lower rates than those found in most other common semiconductor materials, such as Si, GaAs, and GaN