The Preparation Of ZnO Thin Films By L-MBE And The Study Of ZnO-TFT

ZnO, a kind of semiconductor material with a direct wide band-gap, possesses larger exciton binding energy than GaN and is easy to realize ultraviolet excitonic emission at room temperature. In recent years, ZnO has become a popular topic in semiconductor fields for its great potentiality in bright light-emitting diode and short wave-length laser diode.With the development of study,it is found that ZnO is an excellent photoelectric material with many advantages such as high transmitence, low deposition temperature, high breakdown voltage, strong prevention to radiation, high electron saturate excurtion speed and so on. Recently, a research on the field effect transistor with ZnO as a active channel layer (ZnO-TFT) has been made abroad. It is notable that this kind of field effect transistor can be made at low temperature and do not require substrate rigorously. Furthermore, this transistor can be made into entirely transparent. So, it is anticipated to work wonderful in thin film transistor liquid crystal displays (TFT-LCD). On this background, this paper worked on the following aspects: 1.High quality ZnO films was deposited on Al₂O₃, SiO₂/Si,SiNx/Si substrats by laser molecule beam epitaxy(L-MBE) with optimized technics. We foucses on the effect of anneal process on the films including crystal quality, surface morphology, photoluminescence, transmitence, optical band energy, resistivity and so on. Through the study, it is found that anneal process can release stress in the films effectly. It can highten the crystalization of film and improve the photoluminescence. The film which annealed over 500℃ almost cannot be seen any deep level emission in the spectra of PL.This anneal process can also increase the optical transmitence and the resistivity of the film.The preparation of so high quality ZnO films is the base of the realization of the ZnO photoelectrics. 2.On the base of the present study of ZnO-TFT as well as the conditions of our lab,We designs a reasonable structure ZnO-TFT. That is first growing one insulated layer(SiO₂ or SiNx) on p-type silicon substrate, then deposite ZnO layer on this insulated layer by L-MBE, and prapare the drain and source polar to form channel by vaporation equipment and a mask in the end. This is the first filed effect transistor with ZnO as a cative channel layer in domestic. By electric test it is found that the transistor works well on N channel enhancement mode and exhibits excellent saturation and pinch-off characteristics. It has high Ion/Ioff ratio, and the threshold voltage is 17.5V, the mobility rate is 1.05 cm2/V·S. As was stated, ZnO, a promising material, has a good future and can be used in fild effect device.