Fabrication And P-type Doping Of ZnO Thin Film By MOCVD

Zinc Oxide is a semiconductor material that has many applications. Traditionally, ZnO is used in acoustic wave devices (SAW), bulk acoustic devices (BAW), Gas sensors, varistors, and transparent electrodes and so on. Compared with GaN, the most successful wide-band semiconductor material at present, ZnO has many promising advantages: high-quality ZnO with very low defect densities can be synthesized at relatively low temperature; ZnO has large excitonic binding energy (60mev at RT), which promises strong photoluminescence from bound excitonic emissions at room temperature. Furthermore, it has been considered as a prime candidate for ultraviolet light emitting diodes and lasers.However, ZnO has largely failed to live up to its potential, because it has proved too difficult to produce high-conductivity p-type ZnO due to (i) self-compensation by intrinsic defects, (ii) a too deep dopant energy level, and (iii) a too low p-type dopant solubility. According to theoretical prediction, among all possible acceptors, N is the best candidate to produce a shallow acceptor level in ZnO, and several groups have achieved p-type ZnO with N as the dopant. But it either had low N concentration and high resistivity, or was not stable although had high N concentration, but the electrical properties degraded after several days. 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.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. By now, we have grown low resistivity and stable N-doped p-type ZnO thin films using our self-assembly low-pressure MOCVD system.The main content of this thesis is as follows:1 , When the substrate temperature is 420℃ and chamber pressure is 1 Torr, We have grown a high crystalline quality hexagonal ZnO thin film on sapphire with the FWHM of (002) peak by X-ray rocking curve is only 190arcsec.2, A low temperature ZnO thin film on substrate can improve the crystalline quality of ZnO, the optimization of substrate temperature is 420℃.3, We characterize the electronic properties of ZnO thin films deposited on different temperature or variable growth parameters of gas flow rate. And achieved reproducible p-type ZnO with the lowest resistivity of 3.02 Ω cm and the related hole concentration of 1.97×10¹⁸ cm^-3 , the flow rates of NO and N₂O were 40 sccm and 15sccm respectively.4,Four months later, mostly p-type ZnO samples still show p-type conduction. It means the sample which was deposited in our experiment is most stable.5,The relationship between annealing temperature and crystalline quality of ZnO was studied. We also found that a relative rapid thermal annealing can effectively activate N and conduct to p-type trasimission.