Fabrication And Properties Of InN And GaN

Indium nitride is one of aⅢ-Ⅴnitride semiconductor with a direct band gap of 0.7eV. It has the smallest effective electron mass of all the group-Ⅲnitrides,which leads to high mobility and high saturation velocity, and a large drift velocity at room temperature. Due to these properties of InN, it has potential applications in optoelectronic devices, such as LDs and high efficiency solar cells, as well as high frequency (high power) electronic devices. Because InN has a very low decomposition temperature and requires a large overpressure of N, it is very difficult to synthesize. In recent years, the realization of some pivotally technical methods and the development of materials growth and devices technics made InN to be the research focus of the world. There are some reports on thin film deposition of InN by radio frequency reactive sputtering, MOCVD and MBE i.e. Among these methods, MOCVD is the most important and widely used by researchers. But now large-scale application of InN devices is confined for the reason of costly equipments and complicated technics. Many research institutes and universities in the world are trying to grow InN materials with simple and low cost methods.In this dissertation, InN powders have been synthesized by nitriding In2O3 powders in a flow of NH3 at 700℃for 140 min. A very comprehensive investigation is conducted into the optimum nitridation condition, the structural , the component, the chemical bonding states, optical characterization. The thermal decomposition behaviors of indium nitride powders in the air and in the pure nitrogen gas are investigated. The InN thin film was synthesized by ammoniating the In thin film in an open quartz tube inside a horizontal quartz tube. The structural and the surface morphology of these films have been investigated.From the X-ray diffraction (XRD) patterns, It is found that the optimum nitridation condition is at a NH3 flow rate of 500ml/min and at a nitridation temperature of 700℃for 140min. InN powder belongs to the hexagonal structure. The nitridation is incomplete below 600℃and InN can be easily turned into In2O3 above 700℃and decomposed and turned into In and N2 above 800℃. The chemical reaction formula is as follows, In2O3 + 2NH3=2InN + 3H2OIndium nitride can be hydrolyzed easily by air moisture. It is unavoidable that a typical X-ray photoelectron spectroscopy (XPS) wide scan spectrum of indium nitride includes In, N, O and C peaks, among which O and C peaks come from the surface adosorption of CO2, H2O and O2 from air and few In2O3 powders. The thermal stability of InN powders under two different conditions (air, nitrogen gas) are analyzed by using X-ray diffraction (XRD) and Fourier transform infrared (FTIR). InN was steady in the open air below 400℃.A majority of InN was converted into In2O3 when the thermal temperature exceeded 500℃. When the temperature was increased to 600℃, InN was all turned into In2O3. The chemical reaction formula is as follows, 2InN + 3O2== 2In2O3In the environment of nitrogen gas, a few InN powders can be turned into In2O3 powders above 600℃in the purity of N2 gas. As the temperature is increased to 800℃, InN powders begin to dissociate.The In film was deposited on Si (111) using a JCK-500A r.f. magnetron sputtering system. The conditions of sputtering were as follows: the background pressure was 4.0×10-4 Pa; the distance between targets and substrates was 8 cm; the pressure of Ar (99.999%) was 3 Pa. After 30s, N2 (99.999%) instead of Ar was introduced to the chamber. The pressure of N2 was 3 Pa. The In film was grown by sputtering an indium (99.99%) target with r.f. power of 150W for 15 min. XRD and FTIR show that InN film has been grown on Si (111) by nitriding indium film under a flow of ammonia at 700℃for 2 hours.From scanning electron microscopy (SEM) images and transmission electron microscopy (TEM) images of InN films synthesized at the optimum nitridation condition, it can be found that the surfaces of InN films are smooth. and the products are hexagonal InN structure.Indium nitride can be hydrolyzed easily by air moisture. It is unavoidable that a typical X-ray photoelectron spectroscopy (XPS) wide scan spectrum of indium nitride includes In, N, O and C peaks, among which O and C peaks come from the surface adosorption of CO2, H2O and O2 from air and few In2O3.In this paper, GaN films were prepared though magnetron sputtering and ammoniating progress on Si (111) substrates. The two experiment routes are carried out to synthesize GaN films: (1) GaN films are synthesized on In middle layer deposited on Si (111) substrates. (2) GaN films are synthesized on In2O3 middle layer deposited on Si (111) substrates. The influence of nitridation temperature and nitridation time on the properties of GaN films was introduced. The results showed that the nitridation temperature and nitridation time play an import role in the crystal quality and the surface morphology of the GaN films.GaN films are synthesized on In middle layer deposited on Si (111) substrates.The morphology, structure, and components of GaN films were analyzed though X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM). The results showed that nitrided at 900℃for 15 minutes have the best crystal quality and surface morphology.GaN films are synthesized on In middle layer deposited on Si (111) substrates.The morphology, structure, and components of GaN films were analyzed though X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM). The results showed that nitrided at 900℃for 15 minutes has the best crystal quality and surface morphology.