Lithium-nitrogen Codoping P-type ZnO And Their Application In Optoelectronic Devices

Znic oxide (ZnO) has been considered as one of the most promising candidates for application in optoelectronic devices, such as light-emitting devices (LEDs), laser diodes, and photodetectors, for its wide band gap (3.37 eV) and large exiciton binding energy (60 meV). It is accepted that two major issues have to be addressed elaborately towards ZnO-based optoelectronic devices. The first issue is that high quality films have to be prepared, which is a fundamental step towards the p-type doping and future optoelectronic applications of ZnO. The second issue is that efficient p-type doping of ZnO has to be realized, which is indispensable for the formation of p-n junctions, and it is the largest hurdle that hinders the above-mentioned applications of ZnO-based materials. The present work is focused on these two issues, and the following results have been obtained:1. ZnO films have been prepared by a plasma-assisted molecular beam epitaxy (MBE) technique. The origin of the intrinsic donors in ZnO has been investigated. It is found that oxygen vacancy (VO) may be the dominant donor source in ZnO. Based on this conclusion, by adjusting the growth parameters, high quality ZnO films with a residual electron concentration of about 1.5×1016 cm-3 has been obtained. The above results lay a ground for the future p-type doping and optoelectronic applications of ZnO. 2. By employing lithium and nitrogen as dual-acceptor dopant, p-type doping of ZnO films have been obtained. The p-type ZnO:(Li,N) films have hole concentration in the order of 1016 cm-3, and mobility of about 8.7 cm2V-1s-1. We note that p-type doping by employing Li-N as a dual-acceptor dopant shows acceptable reproducibility.3. After obtaining p-type ZnO films, p-i-n structured LEDs were designed and fabricated, and electroluminescence has been observed from the ZnO p-i-n junctions. The dominant emission peak is at around 425 nm, and an obvious purple emission can be observed from the junction area of the structure in the photograph of the structure. It is noteworthy that the LEDs can shows obvious emission after placing for about one month, and the total running time is in the order of tens of hours. The dominant purple emission reveals that the p-type ZnO films obtained via the Li-N dual-acceptor doping process is applicable in the optoelectronic devices.4. ZnO based p-i-n homojunction structured photodetectors have been prepared, and the photodetector exhibited an obvious peak responsivity at around 380 nm under 0 V bias, with a maximum responsivity about 0.45 mA/W. The maximum responsivity of the detector increases with the reverse bias voltage increasing, and it can reach 8 A/W at 10 V bias. The response decay time of the p-i-n structured photodetector is about 260 ns. This is the first report on ZnO based p-i-n homojunction structured photodetector to the best of our knowledge. Considering that p-i-n structure have several figure of merits compare with other structures, the results reported in this thesis may provide a route to high-performance ZnO based ultraviolet photodetectors.