ALD growth of ZnO on p-Si and electrical characterization of ZnO/p-Si heterojunctions

The growth of ZnO on p-Si by thermal atomic layer deposition (ALD) was carried out and the electrical properties of ZnO/p-Si heterojunctions were investigated. The ZnO surface became rougher with increasing the ZnO thickness from 9 to 19 nm. The current–voltage (I–V) characteristics showed the normal p-n junction behaviors for 9 nm thick ZnO whereas those became reversal for 19 nm thick ZnO. In the forward bias log(I)–log(V) plots, the wider linear region was observed for 9 nm thick ZnO. The analysis on the plots of reverse saturation current vs. 1/kT produced the activation energies of 0.11 and 0.42 eV for 9 and 19 nm thick ZnO, respectively, indicating that tunneling occurred through a single type of defects. According to X-ray reflectivity measurements, Zn deficient ZnO layer was formed near the ZnO/p-Si interface for 19 nm thick ZnO. These results suggest that the density of donor-type defects decreased for 19 nm thick ZnO.