Influence of As doping on the properties of nonpolar ZnO

In this paper the properties of nonpolar arsenic (As) doped ZnO films obtained by molecular beam epitaxy on r oriented sapphire were analyzed. Optical and electrical properties of a-ZnO thin films with varying concentration of As were studied by several experimental techniques such as Hall effect measured at room temperature, temperature dependent photoluminescence, transmittance, secondary ion mass spectrometry (SIMS), angle dependent micro-Raman spectroscopy and X-ray diffraction. All as-grown samples showed n-type conductivity but we found that the concentration of As atoms (measured by SIMS) increases much faster with the increase of As effusion cell temperature than the concentration of electrons. Such behavior may suggest an amphoteric nature of the As-dopant and presence of n-type As-related defects instead of the expected p-type ones. The luminescence (PL) spectra strongly depend on the concentration of As-dopant. In particular, at low temperatures, PL lines due to donor-bound excitons ((DX)-X-0) dominate, however the intensity of the (DX)-X-0 lines decreases with increasing As concentration suggesting that isolated As atoms are not responsible for n-type conductivity. In the presented paper it is also shown that the disorder in ZnO layers increases with As concentration and its manifested as an increase of the widths of the luminescence, Raman and diffraction peaks as well as an increase of Urbach energy.

Automated summary

The properties of nonpolar arsenic (As) doped ZnO films grown by molecular beam epitaxy on r oriented sapphire were analyzed in this paper. It was found that the concentration of As atoms increased faster with temperature than the concentration of electrons, suggesting an amphoteric nature of the As-dopant. Additionally, the luminescence spectra strongly depended on the concentration of As-dopant.