Preparation of p-/n- type ZnO:Al thin films by RF diode sputtering for solar and optoelectronic applications

Aluminum - doped ZnO thin films (ZnO:Al) and Al - N co-doped (ZnOALN) thin films were prepared by RF diode sputtering from a ceramic target (ZnO+2 wt. % AI₂O₃) in Ar and Ar/25divide75 %N₂ atmosphere. The ZnOAl films exhibited n-type conduction with a minimum resistivity (2times10^-3 Omegacm), a high visible transmittance (> 82 %, including Corning glass substrate) and an optical band gap E_g ~ 3.3 eV. The p-type doping efficiency of the nitrogen was investigated as a function of the nitrogen content in the sputtering gas. The ZnO:Al:N thin films with p-type conduction were obtained for 75 % N₂ in the Ar/N₂ gas. Their resistivity and the hole concentration were 21 Omegacm and 7.8times10¹⁷ cm^-3 respectively. The micro-Raman scattering measurements revealed N - related local vibrational modes (LVMs) at 276.44 cm^-1 and 518.47 cm^-1 in the spectra of the films grown with nitrogen and proved that the p-type conduction was a result of the nitrogen incorporation and formation of N_O acceptors. The average transmittance (74divide86%, including Corning glass substrate) and E_g (3.22 - 3.10 eV) depended on the N₂ content in the sputtering gas. The p-/n-type ZnO thin films were utilized for preparing p-n heterojunction structures on (100) n-type and (111) p-type silicon substrates. Rectification was clearly observed for both structures.