Synthesis And Characteristics Of P-ZnO Thin Films

Zinc oxide (ZnO) is an II-VI group wide-band-gap (3.37eV) semiconductor with a high exciton binding energy (60 meV) , so it has a lot of applications in short-wave optoelectronic device. Therefore, the country in the world is studying this material actively. The ZnO films, grown on sapphire or silicon substrates, have been investigated by several methods such as Molecular Beam Epitaxy, Sputtering, and metal-organic chemical vapor deposition (MOCVD) and so on. Among them, MOCVD, MBE, and PLD can obtain high quality ZnO films. Besides, MOCVD is adapted to industry manufacture. In this paper, high quality ZnO thin films on sapphire substrate have been obtained by MOCVD system designed by ourselves. At the same time, the properties of doped ZnO films have been investigated in details, and good results have been achieved. Diethyl zinc (DEZn), O2 and N2O were used as precursors in plasma-assisted MOCVD. Different growing temperatures were used to achieve high quality ZnO thin films. The effects of growth temperature on the optical and electronics properties of ZnO thin films, grown on n-Si (100) substrate by plasma-assisted MOCVD, were investigated by X-ray diffraction (XRD), X-ray photoelectron spectrometer (XPS), Photoluminescence (PL), and Hall measurements. The XRD patterns of the samples indicated that the crystallinity of the ZnO films grown in 500℃ was improved. The XPS spectra showed that ZnO films changed from O-rich to Zn-rich after increasing temperature from 400℃ to 500℃. Moreover, Hall measurements indicated that the resistivity in 400℃ (>10~4 O-cm) was higher than that in 500℃ (3.48x10~3O-cm). The PL spectrum also showed that the ultraviolet emission peak in 400℃ was stronger than that in 500℃. By controlling, great changes have been observed in the structural, optical and electrical properties of ZnO films. The film with the best structural and optical quality was grown under a moderate N2O plasma flux of 70sccm, and the highest resistivity is 1.24xl0~5Ocm with an electron concentration of 1.53X10~13 cm~3. As to N doping in ZnO films, N in ZnO films can be produced by R.F. plasma, and the crystal quality and optical characteristic of ZnO films can not be changed. Ultrasonic spray pyrolysis (USP) is used to grow ZnO based films at atmosphere and manufactures light emitting diode (led).