Optical absorption edge shifts in electrodeposited ZnO thin films

Abstract

Electrodeposited wurtzite ZnO thin films exhibit shifts in their optical absorption edges with changes in thickness (0.2 – 2 μm), deposition potential (-0.80 V to -1.50 V), and aging time (days to months under ambient conditions). Increases in absorption edge energy are consistent with H+ incorporation as a shallow donor (Burstein-Moss effect) due to deposition in the presence of electrochemically evolved hydrogen. Diffuse reflectance spectroscopic data and Raman spectroscopic data show both potential- and thickness-dependent changes in defect levels and absorption edges, which suggests that H+ can be trapped in secondary defects. Such defects also increase the diffusion time for H+ and lead to the observed decay in absorption edge energy with aging.