Preparation And Properties Of P-type ZnO:Li By PLD

Zinc oxide (ZnO) with a direct band gap and a large exciton binding energy has recently attracted considerable attention because of its promising applications in UV light emitting diodes (LEDs) and laser diodes (LDs). To realize these device applications, an imperative issue is to fabricate both high-quality p-type and n-type ZnO films. It can be easily doped high-quality n-type, but it is difficult to dope p-type. ZnO has largely failed to live up to its potential due to its "asymmetric doping" limitation, such as self-compensation, deep acceptor level, and low solubility of the acceptor dopants. So the greatest challenge in exploiting ZnO, as in the case of GaN, is in achieving p-type doping.Among group-V elements, N has been used as a popular p-type dopant, while p-type samples have also been successfully obtained with other dopants such as P and As. Theoretically, substitutional group-I elements behave as shallower acceptors, and for LiZn, almost no lattice relaxations occurs around the impurity atom. Thus, Li-doping is really a promising way to fabricate p-type ZnO film with good quality. Nowadays, it is a great breakthrough for our lab to realize the p-type ZnO by Li monodoping using DC reactive magnetron sputtering.Pulsed laser deposition (PLD) technique has been realized to be more useful in growing high quality thin films of metal oxide materials compared with other techniques because of its good features. The system is simple hardware, atomic-layer control achieved by adjusting the laser effluence and the pulse repetition rate, and has the possibility of in situ processing of the multilayer hetero-structures by using the multiple target arrangements.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. Lithium-doped p-type ZnO thin films have been realized by pulsed laser deposition (PLD). The films exhibit good (002) preferential orientation and good transparency of above 85%.2. The effect of substrata temperature on conduction type, carrier concentration, Hall mobility, and resistivity of ZnO thin films have been investigated. The Li-doped ZnO film prepared at 450°C possessed the lowest resistivity of 34 Q cm with a Hall mobility of 0.134cm2V"'s"' and hole concentration of 1.37X 10I8cm"3.3. The effect of pressure of O2 prepared at 450°C on conduction type, carrier concentration, Hall mobility, and resistivity of ZnO thin films have been investigated. The p-type Li-doped ZnO film was realized at the pressure of O2 in rang of 30Pa to 60Pa, with the lowest resistivity of 19.9Qcm, a Hall mobility of 0.144cm2V"'s"' and hole concentration of 2.18 X 10 cm".4. Using N2O replaceing O2 as the atmosphere for preparing Li-ZnO, we realize the p-type ZnO at a lower pressure of N2O.