The Growth Of High Quality ZnO Thin Films At Low Temperature By PECVD & Study Of Its Properties

Recently much attention has been paid to short wavelength lasers for use in high density information storage, information display, UV communication, medical treament & diagnisis, and so on, which make it become an important basal research with extensive application. It is widely accepted that ZnO is one of the most promising materials for producing an ultraviolet laser at room temperature due to its wide direct band gap (Eg=3.3eV) and large excitonic binding energy of 60 meV, which was testified by the results of optically pumped stimulated emission and lasing from ZnO thin films. Like GaN compound, the reasearch about ZnO has burned white hot in the range of wide band gap.To study its properties and obtain high quality thin films, a variety of techniques have been used such as molecular beam epitaxy (MBE), metal organic chemical vapor deposition (MOCVD), magnetron sputtering, pulsed laser deposition, to prepare ZnO thin films. In order to otain high quality ZnO thin films, we, for the first time, employ the plasma enhanced chemical vapor deposition (PECVD) to prepare high quality ZnO thin film at low temperature using a zinc organic source (Zn(C2H5)2) and carbon dioxide (CO2) gas mixtures. The effects of the growing condiction and the native oxide layer of Si substrate on the quality of ZnO thin films was studied in detail. To prepare p-ZnO and overcome the dufficulty of reverse due to the interaction between the N atomic, we obtain high qulaity p-ZnO by a easy way of thermal Zn3N2. The major results lists as following:1 The relationships between the substrate temperature, the gas flow ratio of Zn(C2H5)2 to CO2, and the rf power and the properties of ZnO films are studied in detail. For the first time,we obtain a (002) orientated high quality ZnO thin films with the full width at half maximum (FWHM) of 0.2o located at 34.42o at a low temperature of 180℃.2 The optical properties of ZnO prepared by the PECVD are studied in detail. The relationship between the optical characteristic of ZnO and the preparing condition is studied. A strong excitonic effect on ZnO thin films at room temperature is observed in optical absorption spectra. An excellent free exciton emission with a narrow FWHM of 90 meV is obtained. 3 For the first time, the effects of rf power on the properties of ZnO are studied. With an increase of inputting rf power (6-19 W), the crystal quality of ZnO thin film is improved, however, a further increasing rf power, the crystal quality become poor. The ZnO thin film prepared at rf power of 19 W shows an excellent optical character identified by photoluminescence, a smooth suface testified by AFM. With increasing the inputting rf power further, the intensity of visible band emission increase, on the contrary, the intensity of UV band decreas. The surface also becomes rough as further increasing rf power.4 The cleanout and the passivation of Si surface was carried out by a two-step process to overcome the surface oxide layer and balance the charge between the substrate and epitaxy. By this way, the crystal quality and emission characteristic of ZnO thin films can be improved, which provide a way to resolve the native oxide layer of Si substrate. 6 The Zn3N2 is prepared on focus glass substrate at low temperature. And for the first time, a p-ZnO with a carrier density of 1017?cm-3 is obtained by thermal Zn3N2 in an oxygen ambient. The difficulty can be overcomed that the N atom is not easy to be doped into ZnO. If we control the annealing condition, the residual nitrogen atoms will become acceptors in ZnO:N films. As a result, we can obtain P-type ZnO thin films with a high carrier density. density. Success in realizing p-type ZnO in an easy way will undoubtedly widen the range of application for ZnO in a great extent.