Deposition of Na–N dual acceptor doped p-type ZnO thin films and fabrication of p-ZnO:(Na, N)/n-ZnO:Eu homojunction

Sodium and nitrogen dual acceptor doped p-type ZnO (ZnO:(Na, N)) films have been prepared by spray pyrolysis technique at a substrate temperature of 623 K. The ZnO:(Na, N) films are grown at a fixed N doping concentration of 2 at.% and varying the nominal Na doping concentration from 0 to 8 at.%. The XRD results show that all the ZnO:(Na, N) films exhibited (0 0 2) preferential orientation. The EDX and elemental mapping analysis shows the presence and distribution of Zn, O, Na and N in the deposited films. The Hall measurement results demonstrate that the Na–N dual acceptor doped ZnO films show excellent p-type conduction. The p-type ZnO:(Na, N) films with comparatively low resistivity of 5.60 × 10−2 Ω cm and relatively high carrier concentration of 3.15 × 1018 cm−3 are obtained at 6 at.%. ZnO based homojunction is fabricated by depositing n-type layer (Eu doped ZnO) grown over the p-type layer ZnO:(Na, N). The current–voltage (I–V) characteristics measured from the two-layer structure show typical rectifying characteristics of p-n junction with a low turn on voltage of about 1.69 V. The ZnO:(Na, N) films exhibit a high transmittance (about >90%) and the average reflectance is 8.9% in the visible region. PL measurement shows near-band-edge (NBE) emission and deep-level (DL) emission in the ZnO:(Na, N) thin films.