Role of the radio frequency magnetron sputtered seed layer properties on ultrasonic spray pyrolyzed ZnO thin films

Herein, we investigated structural and electrical properties of ultrasonic spray pyrolyzed ZnO thin films (ZnO(USP)) deposited on radio frequency sputtered ZnO nanocolumns (ZnO(Seed)) under various oxygen atmosphere on p-Si substrates. X-ray diffraction data of the samples showed that the samples had a hexagonal structure with a strong (002) preferred orientation. The grain size of ZnO(USP) samples prepared on the seed layer sputtered in 25% and 50% oxygen atmosphere decreased and surface morphology was nanopebbles. ZnO samples prepared on the seed layers exhibited sharp and predominant ultraviolet luminescence at approximately 380 nm. The current-voltage characteristics of the n-ZnO(USP)/n-ZnO(seed)/p-Si heterojunctions were significantly affected by the seed layer preparation conditions. Backward diode behavior was observed for the n-ZnO(USP)/n-ZnO(seed)/p-Si heterojunctions with high donor concentration, in which the seed layers prepared in 100% and 75% argon atmosphere. The carrier concentration value was decreased for the films with the seed layer, obtained at higher oxygen content in the sputtering atmosphere.