Carrier transport mechanism on ZnO nanorods/p-Si heterojunction diodes with various atmospheres annealing hydrothermal seed-layer

Annealing in various atmospheres (vacuum, N2, and O2) was employed for a hydrothermal seed-layer. The influence on ZnO nanorods (NRs) and carrier transport of ZnO NRs/p-Si heterojunction diodes (HJDs) was investigated. In this work, a hydrothermal method was employed to prepare a seed-layer on a Si substrate, and then annealing at 450 °C in various atmospheres was carried out to improve the subsequent growth of ZnO NRs according to the same method. Observations indicated that ZnO NRs with an O2-annealed seed-layer have a higher nucleation density and absorb fewer OH groups or O2− ions, and hence they have fewer defect-level centres. This leads to a very large rectification ratio of 1.9 × 105 in the ZnO NRs/p-Si HJDs because oxygen atoms compensate for the oxygen vacancy-related defects. More band-gap states are present at the ZnO/p-Si interface for the vacuum annealing sample, and this enables recombination-tunnelling transport with a rather large ideality factor of 7 at forward voltage less than 0.7 V. In contrast, diffusion–recombination transport was obtained in the N2- and O2-annealed samples with ideality factors as low as 2.4 and 2.2, respectively. - Highlights: ► Annealing in various atmospheres (vacuum, N2, and O2) for hydrothermal seed-layers. ► Carrier transport in ZnO nanorods (NRs)/p-Si heterojunction diodes (HJDs). ► Vacuum-annealed ZnO NRs/p-Si HJDs demonstrate recombination-tunnelling transport. ► N2- and O2-annealed ZnO NRs/p-Si HJDs reveal diffusion–recombination transport. ► Large rectification ratio of 1.9 × 105 in the O2-annealed ZnO NRs/p-Si HJDs.