Preparation And Characterization Of AIN Thin Films

In this thesis,A1N thin films are prepared by medium frequency magnetron sputtering.The effects of the substrate temperature and annealing temperature on the studied and properties of A1N thin films have been studied,especially,the optical properties and photoluminescence of the A1N thin films have been studied.Crystallization material A1N,with direct band gap of 6.28eV,is transparent at rear violet region,if doped,A1N thin films,can be used for photoelectronic devices in the range of violet.Because of its high hardness,high thermal conductance,high temperature resistance,corrosion resistant and good temperature adaptation with Si and GaAs,A1N materials are good electronic packaging ones.A1N materials are not influenced by electromagnetism radiation and ions and electrons bombardment.In addition,by alloy of A1N and GaN,AlGaN can be formed,which is very interesting materials,for photoelectronic devices in the range of violet and green.A1N thin films are prepeared generally by reaction magnetron sputtering,RF or DC mode.This technology is cheap.In DC mode,although pure A1 target is used,if sputtered directly,insulating A1N thin films will also be deposited on the target surface and the components in vacuum,resulting in target poison and anode disappearance.In order to solve these problems,medium frequency(MF) power supply and twin targets technique have been employed.In this technique,the twin targets act as negative and positive pole mutually during sputtering.The application of A1N thin films is related to the quality of the films. Therefore,the effect of preparation conditions such as different substrate and substrate temperature and annealing temperature on the microstructure and the properties of the films has been studied to get optimal conditions for good quality of the films.It is formed that A1N thin films on different substrates show different preferred orientation and the performance are also different.The films on quartz crystal substrates are with preferred orientation of(101),the surface are smooth and the crystallites are fine,as examined by AFM.The films on the glass substrates show preferred orientation of(002) which means c axle is vertical to the surface of the samples,better crystallization and a rather large grain size in average.The films on Si substrate show preferred orientation of(100) and(110),the c axle of which is parallel and decline to the surface of the sample,respectively.For A1N thin film on Si substrate,the roughness is relatively large with a preferred orientation of (110) and the weak intensity of XRD is peak for the sample with the substrate temperature of 190℃.The surface roughness,preferred orientation and the intensity of XRD peak would be changed for different substrate temperature.When the temperatures increases farther,it is helpful to prepare the thin films with a preferred orientation of(110),however,the surface roughness will be large.The effect of the annealing condition on the structure and surface topography of A1N thin films is discussed in this thesis.The as-sputtered samples are annealed at different temperature in an atmosphere of N₂.After annealing the surface of the samples would be smooth,generally.It is found that 700℃is optimal annealing temperature.For the samples annealed at a temperature higher than 700℃,the crystallization become worse.1stOpt software is used to obtain the optical constants of the A1N thin films with the help of the physical model proposed by Forouhi and Bloomer by fitting the experimental reflective curve.In the spectral wavelength range of 400-800 nm,refractive index n is 1.9-2.3,and it decreases with wavelength,extinctive coefficient k is less than 0.006,which means the films have good light transmission. It is found that the higher annealing temperature is helpful to obtain the high refractive index of the A1N thin films. The photoluminescence of the samples are studied the position of luminescence spectrum peak is nearly identical and the intensity of the peak is different when a sample is illuminated with different excitation wavelength in the range of violet.The peak of the photoluminescence spectrum is relative to the impurity energy level.Therefore,the result show that various kinds of impurity exist in the sample.For the thin films on different substrate the position of the peak is different.This means that different impurities exist for different substrate.The effect of preparation condition on the photoluminescence and impurities related is also studied by PL.