Zinc oxide heterojunctions and Schottky junctions for ultraviolet detectors.

摘要

The semiconductor ZnO has a band gap of 3.3 eV and has potential in applications as transparent and conducting layers for electronic devices. In the present work, experiments have been carried out to deposit thin films of ZnO on glass and silicon substrates by RF magnetron sputtering. The deposition experiments were performed at substrate temperatures in a range from room value to 400°C. Resistivity measurements were performed on the films. The resistivity increased as the substrate temperature was increased from room value to 400°C. The films on the silicon substrates were then processed into ZnO(n)-Si(p) heterojunctions whereas the ones on glass substrates were processed into metal-ZnO-metal MSM devices. Dark current-voltage and capacitance-voltage characteristics of the fabricated devices have been studied in order to determine the effects of substrate temperature during the deposition. In addition, post deposition heat treatment experiments were performed and the effects were examined by the electrical measurements. For the samples deposited at room temperature, the resistivity was observed to decrease drastically after a heat treatment at 150°C for 30 minutes.;Illuminated characteristics of both the heterojunctions and MSM devices were also studied in a wavelength range from 300 to 700 nm. It was observed that UV responsivity for the ZnO-Si heterojunctions shows an increase from 210 to 300°C and a large decrease at 400°C. Under illumination, the current at given voltage increases for all samples and this has been confirmed to be mainly due to the bandgap absorption. From the post deposition heat treatment experiments carried out at low temperatures, the dark current was observed to increase with heat treatment time. However, the photocurrent was also observed to increase with the heat treatment time.