Study Of Processing And Luminescent Properties Of AlN Films Prepared By Reactive Magnetron Sputtering

Aluminum nitride (AlN) thin films are receiving a great deal of attention due to their potential as materials for optoelectronic devices in the blue to ultraviolet spectral range. In this dissertation, aluminum nitride thin films are prepared on glass substrates by reactive magnetron sputtering, and the processing behaviour and the effect of preparation conditions on the properties of thin films are investigated. In addition, the luminescent properties of copper (Cu) and manganese (Mn) doped AlN films are also studied.In the case of AlN film growth using magnetron sputtering in mixtures of argon and nitrogen, parameters such as the discharge power, the total gas pressure and the N2 partial pressure have a strong influence on the properties of the resulting films and the process. Also, these parameters are often highly interdependent, and the understanding of its underlying physical and chemical processes is still insufficient. In addition, high temperatures are required to attain the AlN films of good quality, which, in most cases, is not compatible with the present semiconductor technology. In this respect, amorphous AlN (a-AlN) films represent an alternative approach to producing compounds at relatively low temperatures. In the present work aluminum nitride films have been deposited on glass by means of reactive magnetron sputtering. The films have been characterized by X-ray diffraction (XRD), energy dispersive X-ray fluorescence spectrometer (EDX) and atomic force microscopy (AFM).The optical properties of the films have been tested by spectrophotometry. XRD results show the amorphous structure of AlN thin films. EDX results confirm the formation of AlN. The optical transmittance is measured as a function of a wavelength by a spectrophotometer. Nitrogen concentrations and target power are the two most important factors on the optical properties of AlN films.There is an optimum nitrogen concentrations and target power that the optical constants is the best. The total gas pressure is also a factor on the optical properties, and the AlN films at lower total gas pressure possess better optical properties.Reactive sputtering processes frequently exhibit stability. That is because that the relationship between the reactive gas flow and the other processing parameter such as deposition rate, film composition, partial pressure of the reactive gas and cathode voltage is very complex and nonlinear and usually exhibits hysteresis effects. To describe the reactive sputtering process of AIN films quantitatively, a new reactive sputtering model has been developed. The model is fundamentally based on a simple reactive gas balance model proposed by Berg et al.in 1988,but includes the change in the secondary electron emission coefficient of target. Calculated results are in good agreement with measurements.The static behavior of the reactive sputtering process of AIN films has been carefully investigated by this model.In addition, the methods of eliminating the hysteresis effect are discussed by this model.It is important to study the dynamic behavior to gain a more complete understanding of the process of AIN films. This work is intended to present a basic model for the dynamic behaviour of the reactive sputtering process. The influence of the processing parameters on the transient behaviour of AIN films is discussed. Because AlN is highly insulating film, the serious problem encountered during the reactive deposition of AIN films is the build-up of an electrically insulating layer on the cathode surface with the resultant charge accumulation and arcing. The arcing can cause severe problems such as inducing defects into the growing film. Now pulsed DC reactive sputtering in the mid-frequency range(10-200 kHz) has developed into an arc-free process under certain conditions. The dynamic model is used to study the arc response characteristic of the process AIN films, and a maximum arc response shutdown time is proposed.Sulfide-based phosphors have dominated the performance, production, and research for thin film electroluminescent (TFEL) device flat panel displays applications, but they have intrinsic problems such as chemical instability and sensitivity to moisture, which make them difficult to pattern the phosphors by chemical etching or photolithography. In addition, owing to their chemical instability, particularly in regard to moisture, sulfide TFEL devices degrade within a short time when operated in the atmosphere. Therefore scientists attempt to find a better phosphor recently. In the past few years, rare earth(RE)-or transition metal(TM)-activatedⅢ-Ⅴnitride, such as AIN films, have received an increasing amount attention due to their unique properties such as higher chemical and thermal stability than sulfide-based phosphors. In addition, AIN films are reported to be an excellent phosphor host material for use in the full-color TFEL display devices since they have a large enough bandgap to emit visible light from the luminescent center without significant absorption. In spite of the advances achieved in this field, RE-or TM-related light emission from AIN is only observed for the films grown at temperature higher than 600℃or after annealing at temperatures of the order of～1000℃. It is desirable to use glass substrate for the deposition of phosphor films from a viewpoint of reducing the production cost, but the softening point of glass substrates is about 600℃.With these points in mind, the low temperature preparation of AIN phosphor layer is one of the most important subjects in developing the devices of this material. Luminescence studies of amorphous AIN doped with pure Mn or Cu were performed at room temperature.Thin films of Mn and Cu amorphous AIN are grown on glass substrates using mid frequency reactive sputtering. X-ray diffraction shows that the films are amorphous. Photoluminescence (PL) measurements are made using a fluorimeter with 325 nm excitation. The AlN:Mn films show a strong emission band at 650nm (FWHM-20nm).A theoretical analysis of the spectroscopic results suggested that Mn ions should be incorporated in tetrahedral lattice sites. Photoluminescence shows that Cu incorporated amorphous AlN films have strong emission in the blue (-430nm). Cu+ ions have the electron configuration of 3d10, and the emission spectra of AlN:Cu results from the 3d94s→3d10. The results indicate the suitability of Cu or Mn doped amorphous AIN films for light-emitting device applications.