We obtain room-temperature resistivities as low as ρ =1.4 x 10^-4 Ω-cm in transparent Ga-doped ZnO grown on Al₂O₃ by pulsed laser deposition (PLD) at 200 °C in 10 mTorr of pure Ar and then annealed in a Zn enfivironment. Donor N_D and acceptor N_A concentrations are calculated from a recently developed scattering theory that is valid for any degenerate semiconductor material and requires only two input parameters, mobility μ and carrier concentration n measured at any temperature in the range 5 - 300 K. By comparison with SIMS and positron annihilation measurements, it has been shown that the donors in these samples are mostly Ga_Zn, as expected, but that the acceptors are point defects, Zn vacancies V_Zn. PLD growth in Ar at 200 °C produces a high concentration of donors [Ga_Zn] = 1.4 x 10²¹ cm^-3, but V_Zn acceptors are produced at the same time, due to self-compensation. Fortunately, a large fraction of the V_Zn can be eliminated by annealing in a Zn environment. The theory gives N_D and N_A, and thus [Ga_Zn] and [V_Zn], at each step of the growth and annealing process. For convenience, the theory is presented graphically, as plots of μ vs n at various values of compensation ratio K = N_A/N_D. From the value of K corresponding to the experimental values of μ and n, it is possible to calculate N_D = n/(1 - K) and N_A = nK/(1 - K).

Date Published: 10 February 2012
PDF: 9 pages
Proc. SPIE 8263, Oxide-based Materials and Devices III, 826302 (10 February 2012); doi: 10.1117/12.910923

Published in SPIE Proceedings Vol. 8263:
Oxide-based Materials and Devices III
Ferechteh H. Teherani; David C. Look; David J. Rogers, Editor(s)