PROCEEDINGS ARTICLE | March 11, 2011

Proc. SPIE. 7940, Oxide-based Materials and Devices II

KEYWORDS: Semiconductors, Scattering, Argon, Electrons, Indium, Phonons, Zinc oxide, Neodymium, Gallium, Temperature metrology

Transparent conductive electrodes are an important part of LCD displays, solar cells, and lightemitting
diodes, but a replacement must be found for indium tin oxide (ITO), which has become
very expensive. One of the prime candidates is ZnO doped with Al, Ga, or In. Here we present a
convenient analytical mobility model that yields donor N<sub>D</sub> and acceptor N<sub>A</sub> concentrations from
Hall-effect measurements at a single temperature, including room temperature (RT). This model
includes scattering from phonons and boundary imperfections as well as from ionized impurities and
point defects. We apply it to films grown by pulsed laser deposition at 200 °C in 10 mTorr of pure
Ar. For a film of thickness 275 nm, the Hall-effect measurements yield a RT resistivity ρ = 1.9 x 10<sup>-4</sup> Ω-cm, mobility μ = 28 cm<sup>2</sup>/V-s, and carrier concentration n = 1.1 x 10<sup>21</sup> cm<sup>-3</sup>, and the mobility
model gives N<sub>D</sub> = 1.6 x 10<sup>21</sup> cm<sup>-3</sup> and N<sub>A</sub> = 4.9 x 10<sup>20</sup> cm<sup>-3</sup>. Also, the transmittance is above 90% in
the visible range. Annealing in forming gas gives ρ = 1.5 x 10<sup>-4</sup> Ω-cm, mobility μ = 42 cm<sup>2</sup>/V-s,
carrier concentration n = 1.0 x 1021 cm-3, ND = 1.1 x 1021 cm-3 and N<sub>A</sub> = 1.0 x 1020 cm<sup>-3</sup>. If the
compensation ratio K = NA/ND can be maintained at about 0.1, and N<sub>D</sub> increased to about 3 x 1021
cm<sup>-3</sup>, then the model predicts a RT resistivity of less than 7 x 10<sup>-5</sup> Ω-cm, well below present ITO
values.