Doping and Compensation in Wide-Band-Gap Oxides*
Wide-band-gap oxides are extensively used as active or passive elements in various electronic and optoelectronic devices. Advantages include transparency, high breakdown voltages, and a wide range of conductivities, from semi-insulating to highly conducting. The conductivities are controlled by donors (ND) and acceptors (NA) so it is important to know their identities (impurities or defects), concentrations, formation energies, and electronic energies (ED and EA). In this talk, we will concentrate on three important oxides, Ga2O3, ZnO, and InGaZnO. The values of ND, NA, and ED, are determined by theoretical fits of temperature-dependent Hall-effect measurements and the donor and acceptor identities are determined by comparison with SIMS and positron annihilation measurements, as well as density functional theory (DFT). For Ga2O3 and ZnO, it is easy to achieve ND > 5 x 1020 cm-3 by doping with Si or Ga, respectively, and indeed we find that ND ≈ [Si] in Ga2O3:Si, and ND ≈ [Ga] in ZnO:Ga. Moreover, the resulting high Fermi levels can drive the formation of native acceptors, Ga and Zn vacancies, respectively, so that, e.g., NA ≈ [VZn] in ZnO:Ga, rather than consisting of impurity-type acceptors. Optical measurements are also affected by the high carrier concentrations; e.g, bulk plasmons can produce a strong reflectance near hν ≈ 1 eV, for n ≈ 1021 cm-3. Finally, we can observe interesting quantum corrections to the resistivity, some following expected theoretical dependences on temperature and magnetic-field strength, and some not.
*Air Force Research Laboratory Sensors Directorate, and NSF (DMR-1305193)
Look, D. C.
(2018). Doping and Compensation in Wide-Band-Gap Oxides*. .