Model for thickness dependence of mobility and concentration in highly conductive zinc oxide

The dependences of the 294 and 10 K mobility mu and volume carrier concentration n on thickness (d = 25 to 147 nm) are examined in aluminum-doped zinc oxide (AZO). Two AZO layers are grown at each thickness, one with and one without a 20-nm-thick ZnON buffer layer. Plots of the 10 K sheet concentration n(s) versus d for buffered (B) and unbuffered (UB) samples give straight lines of similar slope, n = 8.36 x 10(20) and 8.32 x 10(20) cm(-3), but different x-axis intercepts, delta d = -4 and +13 nm, respectively. Plots of n(s) versus d at 294 K produce substantially the same results. Plots of mu versus d can be well fitted with the equation mu(d) = mu(infinity)/left perpendicular1 + d*/(d -delta d)right perpendicular, where d* is the thickness for which mu(infinity) is reduced by a factor 2. For the B and UB samples, d* = 7 and 23 nm, respectively, showing the efficacy of the ZnON buffer. Finally, from n and mu(infinity) we can use degenerate electron scattering theory to calculate bulk donor and acceptor concentrations of 1.23 x 10(21) cm(-3) and 1.95 x 10(20) cm(-3), respectively, and Drude theory to predict a plasmonic resonance at 1.34 mu m. The latter is confirmed by reflectance measurements. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. [DOI: 10.1117/1.OE.52.3.033801]