In this thesis, we will try to grow m-plane InGaN blue light-emitting diodes (LEDs) and discuss the characteristics. First, pure m-plane GaN on the m-sapphire grown by plasma assisted molecular beam epitaxy (PAMBE) had been achieved. ¢½/¢» ratio and the growth temperature are the most important factors in the growth sequence. M-GaN film with better crystal quality was grown successfully by tuning these two factors. Indium composition in the InGaN layer is an important issue in the growth of blue LEDs; In/Ga ratio could affect the bandgap i.e. the target wavelength of a LED. We have to regard the crystal quality and the target wavelength of the InGaN layer in growth procedure. Structural properties were investigated by X-ray diffraction (XRD). XRD measurements showed that the crystal orientation of GaN films was pure m-plane. From cathodoluminescence (CL) spectra, the luminescence wavelength of InGaN layer is in the blue-light range. The crysatalline of m-plane InGaN blue LEDs were analyzed by XRD and Electron Back-Scattered Diffraction (EBSD). Electroluminescence (EL) was measured under the different inject current conditions; the polarization of EL was also measured. Moreover, the current-voltage curve and current-output curve were carried out.

In this article, we report the study of defects between single and bulk GaN nanorods in temperature dependence. High quality of GaN nanorods have been investigated by £g-photoluminescence. Optical properties and surface morphology have been analyzed by a series of measurements, including field-emission electron microscopy (FESEM), and cathodoluminescence (CL). CL data reveal that the intensity of surface state emission is larger than near-band-edge emission at 20K . The 3.21eV peak reveals the structural defect at GaN/Si interface. The surface state emission from bottom is larger than top.

We invistegated the characteristic of GaN grown on LiAlO2 substrate by molecular epitaxy beam. First of all , we try to changed the growth ratio and concluded some relation between the quality of thin film. We expect to improve the quality of M-plane GaN and the size and density of c-plane GaN single-crystals by changing growth conditions. we found that when the N / Ga flow ratio decreased, that is much favor to the growth of M-plane GaN, is not favor to the growth of c-plane GaN. Further research indicates that, on entering the PA-MBE growth prior to phosphoric acid ratio of 1:50 with water to etch the surface of LAO substrate for a minute, is more suitable for M-plane GaN growth, can effectively inhibit Growth of c-plane GaN. The last series of samples, we will LAO substrate into PA-MBE system, DI water before soaking for ten minutes, we found the study can help to improve the c-plane GaN growth.

We will discuss the growth and characterization of AlxGa1-xN/GaN on sapphire substrate by plasma-assisted molecular beam epitaxy. By performing the X-ray diffraction (XRD) of our sample, we could control the fraction of Aluminum in about 0%, 16%, and 31% with varying the equivalent pressure of Aluminum. Under the investigation of field emission scanning electron microscopy (FESEM) and reflection high energy electron diffraction (RHEED) pattern, we can determinate the samples are N-polarity. The photoluminescence (PL) spectra show the bowing coefficient of AlGaN is about 1.38 eV. Furthermore, The Hall mobility could be improved from 8.2 cm2/Vs to 453 cm2/Vs or 796 cm2/Vs at room temperature or liquid nitrogen temperature respectively, after changing the structure of AlxGa1-xN, such as fraction of Aluminum, the thickness of i-AlxGa1-xN and n-AlxGa1-xN, and cap layer.

The materials based on GaN have successfully developed on short-wavelength laser diodes (LDs), light-emitting diodes (LEDs) and ultraviolet photodetector. In this study, GaN epitaxial layers have been successfully grown on sapphire substrates. We used several methods including the growth temperature and time of amorphous nucleation layer before growing epilayer and the growth temperature of GaN epilayer to study it. From the results of the photoluminescence (PL) measured at 77K, the X-Ray diffraction measurement, SEM cross sectional views to realize the characteristic and we get a better qualities of GaN epilayers after using the foregoing methods. In this study, the re-crystallization of the amorphous nucleation layer would occur while temperature re-rise to high temperature, and the phenomenon have different crystallinity under the different growth conditions of nucleation layer, which influence the quality and morphology of GaN epilayers seriously. According to the results of the experiments, we study the mechanisms of yellows luminescence and donor-acceptor pair.

Using a numerical method to simulate the Metal-Organic Chemical Vapor Deposition (MOCVD). A study of the GaN films were growth on sapphire substrates, and a new design method which The position of carrier gas inlets and outlets, the gas in inlets by a showerhead reactor, the modified susceptor. The purpose of this research is to maintain deposited GaN film thickness variation range by controlling those parameters which may affect the deposition.

Using contactless Electroreflectance spectroscopy to determine the face terminate of GaN.

The first-principles calculation method has been used to calculate the total energy and the dipole moment per disk of an array of four-atomic-layers thick GaN nanodisks as functions of their separation. The dipole moment per disk is found to increase with the separation of the disks and saturates at a separation between the edges of neighboring disks of about 11Å. This trend indicates that there exists a charge transfer effect, which gives rise to a dipole moment in opposite direction to the dipole moment associated with the two Ga-N bilayers when disks are close enough. The approximate total energy after the adjustment of the charge transfer effect is found to decrease with the increase of the separation of disks, which indicates that the intrinsic dipoles of the nanodisks gives rise to repulsive interactions among them.

The main purpose of this study is focused on the defects within the layers of GaN over AlN thin films which were grown on the substrates of silicon (111) and LiAlO2 (100), respectively. The growth of three sapphire crystals is also addressed. During the epitaxial growth period, the Al pre-deposition time is very important for the defect on AlN/Si, and due to the high stacking fault energy, the partial dislocations in the AlN layers can not be observed. Cracks were found in the GaN films because of the great thermal mismatch between GaN itself and AlN which is up to 25%. Although the lattice mismatch between GaN and LiAlO2 is low, the thermal stress effect still could not be avoided. Cracks also occurred in the GaN films which were grown on LiAlO2 substrates. For the sapphire pulled along [100] direction, the crystal has fewer amounts of bubbles at the lower rotation rate. For the sapphire pulled along [001] direction, the crystal with 4.5 mm/hr pulling rate has cracks along [001] direction, but the crystal with 4.0 mm/hr pulling rate has no cracks inside.

In this study, we discussed the capacitance-voltage characteristics of the GaN MOS structure with surface treatment using low energy ion beam prior to the oxide deposition. We used the E-Beam evaporator which was equipped with the ion beam assisted deposition system that originally used for optical thin film deposition. Before depositing SiO2 the surface was treated by low energy Ar+ with different processing time inside the vacuum chamber around 10-6 torr. The purpose was to reduce the density of interface states and to explore the influence of C-V characteristics of the GaN MOS structure. We have measured the high frequency C-V curve, hysteresis, and also varied the delay time while measuring. Based on the measuring results, some useful parameters of the device were obtained. Found that the deep depletion phenomenon and hysteresis were easy seen in high frequency C-V measurement. To lower the interfacial states of the sample and shorten the processing time of the low energy ion beam treatment yielded the better result.But the surface was easily damaged when the processing time was prolonged.At last we added the capacitance-voltage study of the Si MOS structure with surface treatment using low energy ion beam, and the capacitance-voltage study of the InN MOS structure.