In this thesis, we discuss the structural properties and quality of GaN-based material structures grown on sapphire¡BLAO and silicon substrates by X ray diffraction pattern. According to 2theta scan, we estimate the Al and In concentration in AlGaN and InGaN films. The thickness of InGaN/GaN multiple quantum wells can also be got from 2

We study AlGaN/GaN heterostucture using temperature dependent micro-photoluminescence. Detailing its principle, operation process and analysis is to provide usage experiences for posterity's reference. The experiment's results emphasize analysis in the photoluminescence spectrum of the GaN in the heterostructure. We believe the peaks 3.486eV, 3.405eV and 3.310eV provided from Free Exciton A, FXA-1LO and FXA-2LO respectively by experience in the cultural heritage.And the fitting result of FXA peak with Gaussian curve shows the major peak is composed by (D0,X), FXA and FXB. Finally, we analyze the major peaks' characteristics varied with the temperature.

Electroreflectance (ER) spectra of Schottky-barrier Au/n-GaN have been measured at various dc biased voltages (Vbias). The ER spectra have exhibited excitonic signals beneath band-gap energy (Eg ). In addition, Franz-Keldysh oscillations (FKOs) were also observed above Eg. The FKOs come from the former region, and the excitonic signals come from the latter region. When Vbias = 0, they are mixed. As reverse Vbias is increased, they become more separated. Furthermore, strength of surface electric field (Fs) can be deduced from the period of the FKOs. From the plot of versus Vbias, barrier height of 1.2 V and carrier concentration were obtained.

We invistegated the characteristic of GaN grown on LiAlO2 substrate by molecular epitaxy beam. We observed the c-plane GaN crystalls assembled at the step-edge of M-plane GaN terraces, with 200 nm ~ 600 nm diameter and 300 nm height. Furthermore, we also observed that there are two kinds of formations for c-palne GaN: one is grown from the hexagonal plane of LAO, the other is transformed from the defeat of M-plane GaN. In addition, we changed the growth ratio and concluded some relation between the quality of thin film and roughness of surface. 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.

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 nitridation temperature for substrates before growing epilayer, the growth temperature and time of buffer layer 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 buffer layer would occur while temperature re-rise to high temperature, and the phenomenon of conglomeration influence the quality and morphology of GaN epilayers. According to the results of the experiments, we study the mechanisms of yellows luminescence and donor-acceptor pair.

ABSTRACT In this thesis we deposit GaN films by magnetron rf sputtering with changes substrate temperature. The electron probe microscope analysis ( EPMA ), scanning electron microscope ( SEM ), photoluminescence measurement ( PL ) and X-ray diffraction ( XRD ) had been used to investigate these GaN films. We find GaN films crystalline quality deposit at low temperature is better then deposit at high temperature. From EPMA analysis we know higher substrate temperature lower oxygen amount of film. The ratio of Ga to N is 1.18 ~ 1.83 in average. The growth rate is about 0.30 £gm/h ~ 0.35 £gm/h in average. Thus changes substrate temperature do not influence growth rate obviously. From SEM and EDS analysis we find the roughness magnitude of films growth on sapphire substrate was smaller than the films growth on silicon substrate. We also find lower substrate temperature the roughness magnitude of films larger on silicon substrate.

The GaN-based materials have successfully developed on short-wavelength laser diodes (LDs), light-emitting diodes (LEDs) and ultraviolet photodetector. Indium-tin-oxide (ITO) thin films have been studied extensively in the optoelectronic industry because they combine unique transparent and conducting properties. ITO thin film is a highly degenerate n-type semiconductor which has a low electrical resistivity of 2-4¡Ñ10-4 £[cm. The low resistivity value of ITO films is due to a high carrier concentration because the Fermi level (EF) is located above the conduction level (EC). The degeneracy is caused by both oxygen vacancies and substitutional tin dopants created during film deposition. Furthermore, ITO is a wide band gap semiconductor visible and near-IR region of the electromagnetic spectrum. Due to these unique properties, ITO has been used in a wide range of applications. In this study, we deposited InSnO film on n-type and p-type GaN by thermal evaporator to overcome the confrontation between brightness and current spreading in optoelectronic devices. According to the experimental results, we study the mechanisms and characteristics of InSnO on GaN. Photoenhanced wet etching of GaN has recently been identified as a means of greatly improving the chemical reactivity of GaN at room temperature. Ultraviolet illumination is used to generate electron-hole pairs at the semiconductor surface, which enhance the oxidation and reduction reactions within an electrochemical cell. We have previously studied a photocnhanced wet etching process n-type GaN using HeCd laser illumination and KOH solution. In this study, etch rates of approximately 300nm/min were obtained.

We have fabricated the device of High Electron Mobility Transistor(HEMT) on Al0.18Ga0.82N/GaN heterostructures. The mobility of 2DEG of the AlGaN/GaN is 9328 cm2/Vs and carrier concentration is 7.917 1012 cm-2 obtained by conventional van der pauw Hall measurement at temperature of 77 K. We made the conducting channel of nanometer wires on the AlGaN/GaN heterostructures for researching low-dimensional transport of two-Dimensional Electron Gas by gate controlled. From the SdH measurement, we can clearly observe the SdH oscillations and obtain the SdH frequencies. For the sample of 0922GaN-200 nm and 0922GaN-100 nm at 0.39 K,two constituted peaks of Gauss¡¦s function were fitted by Non-linear Curve and Two SdH oscillations beat each other, probably due to spin-splitting. However, we can¡¦t discover any trend in the experiment of gate controlled. In the future, we will try to improve the quality and discover the suitable depth of SiO2.

In this thesis, we investigated the growth of nonpolar GaN on (100) £^¡VLiAlO2 substrate by a simple chemical vapor deposition (CVD) process. Metallic gallium, NH3 and ultra-purity nitrogen were used as Ga, N sources and carrier gas. The X-ray diffraction and scanning electron microscopy were used to study the influence of growth conditions such as reaction pressure, growth temperature and deposition time on the GaN epilayer¡¦s orientation and surface morphology. It¡¦s found that pure c plane, c mixed m plane and pure m plane GaN epilayers can be grown on LiAlO2 substrates by the change of growth temperatures (950¢XC~1050¢XC) under 200 torr pressure and NH3/N2 (450/450sccm) gas flow. In addition, with longer deposition time (30min ~120min), nonpolar GaN epilayers show better crystal quality. Furthermore, atomic force microscopy, Raman spectroscopy, cathodeluminescence, transmission electron microscopy were used to study the surface morphology, stress, optical properties and microstructure of the nonpolar GaN epilayers.

In this thesis, we study the magnetro-transport properties of Fe-doped AlxGa1-xN/GaN heterostructure with different Al content by Shubnikov-de Haas measurements. On the samples KTH640(x=0.294)¡BKTH643(x=0.344)¡BKTH642(x=0.390)¡BKTH644 (x=0.397), we find that the electron have occupied the lowest two subbands, and the energy separation for each sample before illumination is 98 meV¡B107 meV¡B111 meV¡B119 meV. On the samples KTH641(x= 0.216)¡BKTH640(x= 0.294)¡BKTH642(x= 0.390)¡BKTH644(x= 0.394), we observe the electrons have spin splitting phenomenon, and the highest spin splitting energy separation¡¦s value in our experiments is 10.6 meV. For all six samples have persistent photoconductivity effect¡¦s behavior after illumination.