Enhancement of Al-N co-dopant solubility in ZnO by high temperature thermal annealing

Abstract

In this paper, we have developed a method to enhance the Al-N co-dopant solubility in bulk ZnO prepared by solid state reaction method. Reactive donor Al and acceptor N were mobilized by annealing the samples at various temperatures from 650 to 850 °C with a step of 50 °C in a programmable furnace. The solubility enhancement argument was verified by the conductivity measurements which showed that the conductivity of annealed films increases as the annealing temperature increases. The activation energy was calculated by the Arrhenius plot and was found to be (0.08 eV) very close to activation energy of shallow acceptor (nitrogen). To further strengthened our argument, we have also performed XRD, FTIR, Raman Spectroscopy and SEM measurements. XRD data suggested that only ZnO phases were present and no evidence for the presence of AlN, Al2O3 or Zn3N2 phases. We have also observed weakening and peak shifting of (002) with annealing temperature that suggested the incorporation of more acceptor defects in the crystal of ZnO. FTIR results verified the presence of Zn-O bond (437 cm−1) along with week vibration of Al-N bond at 917 cm−1. Raman spectroscopy data consists of 2E2, A1 (LO) and E2(high) modes of ZnO but sample annealed at 800 °C has additional nitrogen related mode at 507 cm−1. SEM images demonstrated the crystalline nature of samples having smooth surface but sample annealed at 800 °C has rough surface which indicated the enhancement of acceptor defects density.