| ZnO is currently receiving much attention due to its fundamental advantages over its main competitor GaN in the request for blue/ultraviolet emitters and detectors, and high-speed electronic devices. One of the greatest difficulties, however, is reliably fabricating p-type ZnO with wide-range hole concentration, high mobility, and low resistivity. Although substantial research is currently being carried out world wide towards this goal, the effective p-type dopant and its doping process have not yet been identified, which significantly hinders the development of ZnO-based optoelectronic and electronic devices.; In this dissertation, group V elements N, P, Sb, and Bi have been used as primary dopants to make ZnO p type. By mixing N2 and O2 through a radio-frequency plasma source with proper ratios, N-doped p-type ZnO films were successfully achieved with a molecular-beam epitaxy system. However, the highest hole concentration was obtained only in the level of 1016 cm-3, which results from the low solubility of N and/or incomplete N activation in ZnO. For phosphorus doping, a GaP effusion cell was used to provide a high-purity P2 beam as the phosphorus dopant source. A narrow growth window was identified to produce p-type ZnO films with high hole concentration in the range of 1.2--6.0 x 1018 cm -3. But the conduction type heavily depends on the growth conditions. To seek better p-type dopant candidates, Sb was tried. It shows that Sb-doped ZnO on Si (100) possesses reliable and superior p-type conduction with high concentration of 0.13--1.7 x 1018 cm-3, Hall mobility of 20.0--28.0 cm2/V s, and resistivity of 0.2--1.7 O cm. Finally Bi, as the last element of group V has been attempted. Bi-doped ZnO films show a decrease of electron concentration as the increase of Bi incorporation.; Based on the successful fabrication of Sb-doped p-type ZnO, a p-ZnO/n-Si p-type Schottky diode was fabricated. The current-voltage measurements show good rectifying characteristics. Electroluminescence was observed under both forward and reverse biases with yellow-band emission at 570-600 nm. Compared with the low-temperature photoluminescence, this emission was found to originate from oxygen interstitial deep levels, where electrons and holes recombine with each other to generate photons. |
