X-ray photoelectron spectroscopy (XPS) is used to compare the composition as a function of depth of as-grown ZnO films heavily doped with Ga and similar samples annealed in air for 10 min. at 600 °C, with particular attention given to the near-surface region. These films were grown by pulsed laser deposition (PLD) using a ZnO target containing 3 wt% Ga₂O₃. The electrical properties of these samples were determined from temperature-dependent Hall-effect measurements. The as-grown film has the following characteristics: i) a ~1:1 Zn:O ratio with a Ga concentration of ~ 3.3 atomic percent; ii) no excess Ga in the near-surface region; and iii) excellent electrical characteristics: ρ=2.42×10^-4 Ω-cm, n=8.05×10²⁰ cm^-3, and μ=32.1 cm²/V-s at 300 K. For the annealed sample: i) the Zn:O ratio remains ~ 1:1, but the Ga concentration is ~ 3 atomic percent which is ~10% lower than in the as-grown film; ii) ~7 at% Ga is measured in the near-surface region; and iii) a significant increase in resistivity to ρ = 0.99 Ω-cm, n = 1.97×10¹⁸ cm^-3, and μ=3.2 cm²/V-s at 300 K. Analysis of the O chemical shift suggests formation of a mixed ZnO/Ga₂O₃ surface layer ≤ 5 nm thick accounts for the observed changes in the Ga profile after annealing.

Date Published: 18 March 2013
PDF: 8 pages
Proc. SPIE 8626, Oxide-based Materials and Devices IV, 862606 (18 March 2013); doi: 10.1117/12.2009394

Published in SPIE Proceedings Vol. 8626:
Oxide-based Materials and Devices IV
Ferechteh Hosseini Teherani; David C. Look; David J. Rogers, Editor(s)