Electrical Properties of DC Reactive Magnetron Sputtered ZnO:Al Films from Optical Spectra

Abstract

Reactive direct current (DC) sputtered ZnO:Al films were prepared using the plasma emission monitoring (PEM) system. Films were deposited using PEM setpoints ranging from 50 to 80%. Transmittance and reflectance of the films were measured by using the UV-VIS-NIR Lambda 900 double beam spectrophotometer. The sheet resistance was measured using the four-point probe. Films optical spectra were fitted with the Drude model to determine their charge carrier concentration, mobility and the alternating current (AC) resistivity. The highest values of mobility and charge carrier concentration were 8.31cm²/Vs and 2.14 x 10^21cm-3 respectively. The lowest value of the AC resistivity was given by the ZnO:Al film with the highest value of the product (Nμ) of charge carrier concentration (N) and mobility (μ). The DC and AC resistivity were of the same orders of magnitude. The optical bandgap was found to increase with the increase in charge carrier concentration. A linear variation of N^2/3 with the optical bandgap, which concurs with the
Burstein-Moss shift theory, was obtained.

Keywords: ZnO:Al, PEM, Drude model, transmittance, reflectance, sputtering.