Plasma-activated nitrogen-doped p-type ZnO thin films with multi-buffer-layers grown on sapphire (0 0 0 1) by L-MBE

Nitrogen-doped ZnO (ZnO:N) thin films with multi-buffer-layers, Mg_0.1Zn_0.9O / ZnO super-lattice structure, were grown on sapphire (0 0 0 1) by plasma-activated laser molecular beam epitaxy (L-MBE) using an atomic nitrogen source. High resolution X-ray diffraction (HR-XRD) measurement demonstrated that all the ZnO:N samples are (0 0 0 2) oriented and the residual strain along c-axial are effectively controlled. Room temperature (RT) Hall measurements indicate that the 200 °C sample shows a p-type behavior with a mobility of 4.08 cm²/V s and a carrier density of 1.47 × 1 0¹⁷ cm^-3. The 300 °C sample shows a weak p-type behavior with a mobility of 0.75 cm²/V s and a carrier density of 4.40 × 1 0¹⁶ cm^-3. However, the 200 °C sample is not stable and reverted back to n-type conductivity in about 5 days. The X-ray photoelectron spectra (XPS) of N1s display two peaks at 404 eV and 396 eV which are related to (N₂)_Oand N_O, respectively. The 10 K low temperature photoluminescence (PL) spectra of the 200 °C sample exhibits an acceptor bound exciton peak at 3.351 eV and a donor-acceptor pair (DAP) peak at 3.228 eV, associated with N_O acting as acceptors.