The Study Of Fabrication And Properties Of Phosphorus-doped P-type ZnO Thin Films By MOCVD Method

Zinc oxide (ZnO) is a direct-bandgap optoelectronic semiconductor, which is widely used in surface acoustic wave devices (SAW), bulk acoustic wave devices (BAW), Gas sensors, varistors, and transparent electrodes and so on. In particular, it has been considered as a prime candidate for ultraviolet light emitting diodes (LEDs) and laser diodes (LDs) due to the larger exciton binding energy (60 meV, versus 25meV for GaN) at room temperature, and this property should translate to an even brighter light emission than that obtained with GaN photonics.To realize these device applications, an imperative issue is to fabricate both high-quality p-type and n-type ZnO films. However, ZnO has largely failed to live up to its potential due to its "asymmetric doping" limitation. It can be easily doped high-quality n-type, but it is difficult to dope p-type. So the greatest challenge in exploiting ZnO, as in the case of GaN, is in achieving p-type doping. Group-V dopants have been considered as possible dopants for p-type ZnO, and nitrogen is most similar to O in terms of atomic size. While Several groups have claimed achievements of p-type ZnO by doping with the acceptor NO, there is still lack of reliable and reproducible p-type doping. To further pursue p-type ZnO, other group-V dopants have been tried. Several research groups have recently reported p-type conductivity in ZnO with large-size-mismatched dopants such as P, As, and Sb. Interestingly, ZnO:P thin films showed good stability and reproducibility.A few papers have claimed achievements of p-type ZnO by radio-frequency sputtering, pulsed laser deposition (PLD), molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD). And among these methods, MOCVD has the advantage of potential industrial application, and is frequently employed for the growth of ZnO. So, it is very important if reliable p-type ZnO could be realized by MOCVD.In this thesis, based on a comprehensive review of the theories and fabricating techniques of ZnO material preparation and p-type doping, we conducted a detailed study of ZnO p-type doping.The main content of this thesis is as follows:1. Phosphorus-doped p-type ZnO thin films have been realized by metalorganic chemical vapor deposition (MOCVD). The films exhibit (002) preferential orientation and good transparency of about 90%.2. The effect of substrata temperature and growth parameters of gas flow rate on conduction type, carrier concentration, Hall mobility, and resistivity of ZnO thin films have been investigated. The p-type ZnO thin films grown at 420°C has the lowest resistivity of 11.3 Q. cm and the highest hole concentration of 8.84x 1018 cm"3.3. Annealing was treated at 550°C under atmosphere for all the films grown at the O2 flow rate of 40sccm and DEZn flow rate of 20|im/min. The electrical properties were improved comparing with the as-grown samples.