Nanostructure, optical and electrical properties of p-NiO/n-Si heterojunction diodes

Evolutions on structural, morphological, optical and electrical characteristics of Pt/p-NiO/n-Si/Al thin-film heterojunction diodes before and after various thermal annealing temperatures have been investigated in details. Increases in the annealing temperature improve the crystalline structures of the films, i.e., stress on the film decreases and grain size of the film increases after annealing. The surface roughness of the films enhances from 3.60 to 4.59 nm, especially after 600 degrees C annealing. This rise in the surface roughness is possible due to the increase in the grain size of the films which causes swelling effect after high-temperature annealing. The energy band gap of the NiO films changes from 3.43 eV to 3.34 eV after annealing temperature up to 450 degrees C, while it slightly increases after 600 degrees C annealing process. These observed variations on the band gap values are due to the changes on the crystalline, microstructure and interfacial parameters of the films. On the other hand, the surface modifications also affect the electrical characteristics of the heterojunction diodes. The lowest sheet resistance is obtained to be 65.2 Omega /sq after 450 degrees C annealing process. Reverse saturation current increases up to 34.1 nA and barrier height also decreases from 0.82 eV to 0.75 eV depending on the annealing temperature. In addition, the lowest value of the ideality factor is obtained to be 1.51 for the diodes annealed at 450 degrees C. It can be concluded that the annealing-induced surface modifications significantly affect the electrical performance of the diodes and the optimum annealing temperature is 450 degrees C for the heterojunction diode applications of the p-NiO/n-Si films.