The Impact of Carbon on Electronic Structure of N-Doped ZnO Films: Scanning Photoelectron Microscopy Study and DFT Calculations.

Abstract

A Scanning Photoelectron Microscopy (SPEM) experiment has been applied to ZnO:N films deposited by Atomic Layer Deposition (ALD) under O-rich conditions and post-growth annealed in oxygen at 800 °C. State-of-the-Art spatial resolution (130 nm) allows for probing the electronic structure of single column of growth. The samples were cleaved under ultra-high vacuum (UHV) conditions to open atomically clean cross-sectional areas for SPEM experiment. It has been shown that different columns reveal considerably different shape of the valence band (VB) photoemission spectra and that some of them are shifted towards the bandgap. The shift of the VB maximum, which is associated with hybridization with acceptor states, was found to be correlated with carbon content measured as a relative intensity of the C1s and Zn3d core levels. Generalized Gradient Approximation (GGA) supplemented by +U correction was applied to both Zn3d and O2p orbitals for calculation of the VZn migration properties by the Nudged Elastic Band (NEB) method. The results suggest that interstitial -CHx groups facilitate the formation of acceptor complexes due to additional lattice perturbation.