AlN thin films grown on GaN/Sapphire substrate by RF magnetron sputtering technique with AlN target has been studied. Simple MIS capacitor was fabricated in order to evaluate the electrical properties of AlN films that played as a insulator. Various microstructures of AlN thin films can be obtained by controlling the growth parameters, such as sputtering powers, sputtering distances and working pressure. The microstructures of the AlN films were examined by X-ray diffraction. The observation of the surface morphology ,the distribution of defects and the interface of AlN/GaN were performed by transmission electron microscopy. The results showed that the amorphous AlN thin films were obtained with a 21cm long sputtering working distance and under the 100W sputtering power and 8mtorr working pressure conditions. The results of the C-V measurement indicated that the MIS device demonstrated a capacitor behavior, however a large leak current showed up in the end. The quality of the AlN films and the process procedures of MIS device still need be improved further.

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 pre-baking treatment for sapphire substrates before growing epilayer, the growth temperature 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 pre-baking treatment for sapphire substrates can 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 (DAP).

In this thesis, we will discuss that GaN template which was grown on the sapphire by metal organic vapour phase epitaxy (MOVPE). Then GaN epi-layer, intrinsic AlGaN (as spacer) and N-type AlGaN(doping Si) which offers carrier grow by molecular-beam epitaxy. We changed the content of aluminium to find out any difference on AlGaN/GaN heterostructure . For our experimental, we tried our best to keep all the parameters in steady besides the vapor of aluminum. If the vapor of aluminum every 4.65*10-9 torr is set to be one unit, then ratio of the pressure from sample A to E is 0.5, 1.0, 1.5, 2 and 3. We can get the best growth parameters by hall measurement, reflection high-energy electron diffraction, scanning electron microscope, atomic force microscopic and X-ray diffraction analysis to improve the quality of the sample. From scanning electron microscope and reflecting high energy electronic diffraction picture, the roughness of all samples is good which confirms that the samples should be in two-dimensional (2D) growth mode. We can find the same result by atom force microscope. After comparing 3D picture, we find out the surface of Sample B is the smoothest, meanwhile the roughness is 1.404 (nm) has been calculated through the functions. Due to Hall measurement in 77 K, the electron mobility of this series of samples are very high, especially Sample C is 10995(cm2/Vs) and sample D is 10697 (cm2/Vs) respectively. Quite narrow Full Width at Half Maximum(FWHM) of AlGaN which is about only 300 (arcsec) has been showed under the analysis of X-ray in rocking curve mode and these results indicate these samples have extraordinary qualities better than previous one.

We discussed the electronic properties in AlxGa1-xN/GaN heterostructures. There are six different samples of AlxGa1-xN/GaN we prepared for this experiment, three of them are undoped AlxGa1-xN/GaN with different x values which is 0.17, 0.29 and 0.33, respectively. The others are Fe-doped AlxGa1-xN/GaN which the x value is 0.18, 0.19 and 0.21 for each sample. Comparing these two types¡¦ materials¡¦ results, we tried to confirm the impurity¡¦s characteristic in our samples. From the Hall measurement results, carrier concentration of Fe-doped AlxGa1-xN/GaN were pretty lower than undoped AlxGa1-xN/GaN, and the mobility at 4.2 K are almost two times to undoped AlxGa1-xN/GaN. At the same time, we performed Shubnikov-de Hass measurement, and two subbands of the 2DEG were populated on the samples for x value is 0.29 and 0.33. The energy separation for first two subbands is 109meV. We also observed obvious beat pattern in the SdH oscillations due to the spin splitting on the samples and the greatest spin-splitting energy is 5.96meV in our measurement. Furthermore, we observed evident PPC effect on the samples of Fe-doped AlxGa1-xN/GaN, the carrier concentrations increased at least 23% after illumination. Meanwhile the samples of undoped AlxGa1-xN/GaN can just produce 10.7% increment at most.

We invistegated the characteristic of GaN nanostructure grown on£^-LiAlO2 substrate by molecular epitaxy beam. We observed the c-plane GaN pillar and M-plane GaN terraces assembled at the LiAlO2 substrate. It was found that the [0001 ¡Â] disk was established with the capture of N atoms by most-outside Ga atoms, while the pyramid was obtained due to the missing of most-outside N atoms. To continue, the photointensity of cathode luminescence excited from the pillar structure was one order of amplitude greater than that from M-plane.

This thesis discusses the crystal quality and transition of electrons and holes pairs by temperature- and power- dependent Photoluminescence (PL). With the PL spectra, we apply four kinds of Internal Quantum Efficiency (IQE) formulas for c- and m- plane III-nitride and discuss the differences of the four formulas. An analysis of IQE is performed and it is found for m-plane III-nitride being larger than c-plane III-nitride. This result confirms that characteristic m-plane structure can increase its radiative recombination.

No description available.

"Guo li Taiwan shi fan da xue guo wen yan jiu suo shuo shi lun wen."

"Guo li Taiwan shi fan da xue guo wen yan jiu suo shuo shi lun wen."

Orientador: Aguinaldo Robinson de Souza / Banca: Jose Humberto Dias da Silva / Banca: Armando Beltran Flors / Banca: João Batista Lopes Martins / Banca: Nelson Henrique Morgon / Resumo: Este trabalho é resultado de um estudo teórico sobre o GaN e o Semicondutor Magnético Ga1-xMnxN, tanto para bulk (sólido) como para as superfícies nanoestruturadas mais estáveis, dada sua importância para o desenvolvimento como material spintrônico. Analisamos deste material suas propriedades estruturais, energéticas e eletrônicas, a partir de cálculos periódicos baseados na teoria do Funcional da Densidade (DFT), como o funcional híbrido B3LYP, e também apresentamos resultados preliminares do estudo das propriedades magnéticas deste material. Realizamos um estudo pormenorizado das estruturas de bandas e da densidade de estados, do Ga1-xMnxN bulk (x~0,02 a 0,18) quanto em superfícies (x~0,0 a 0,17) para os modelos de supercélula de 32 e 96 átomos bulk e modelos de superfícies com 12 e 24 camadas. Os resultados obtidos nos mostram que para concentrações acima de 6% ocorre um acréscimo na distância de ligação Mn-N na direção c, pelo fato do Mn apresentar um raio atômico superior ao Ga e propriedades físicas e químicas distintas. Para os cálculos com superfícies, foi realizada a substituição do Ga por Mn em diferentes posições relativas na superfície, sub-superfície e core, ocorrendo o aumento da energia total conforme os átomos de Mn se movem para os sítios mais internos da superfície e ao considerar a forma de equilíbrio baseada na estabilidade termodinâmica, os valores das energias superficiais das superfícies (1010) e (1120) do GaN wurtzita são as mais estáveis para a concentração de ~8%. Com o aumento da concentração, ocorre nas estruturas de bandas uma diminuição do gap, tanto para o bulk quanto para as superfícies, porém ele se mantém direto no bulk, com exceção para concentração de 18% e, na superfície (1010), enquanto que na superfície (1120) o gap é indireto... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: This work is the result os a theoretical study concerning GaN and the Magnetic Semiconductor Ga1-xMnxN, in both the bulk and the most stable nanoestructured surfaces, due to its importance in the development as spintronic material. We analyze the structural, energetic and electronic properties of this material, by means of periodic calculations based on the Functional Density Theory (DFT), at the hybrid functional B3LYP level, and also present the preliminary results of the study of the magnetic properties of this material. We carried out a detailed study of the band structures and the density of states, for both the Ga1-xMnxN bulk (x~002 a 0,18) and its surfaces (x~0,0 a 0,17) using supercell models constitued by 32 and 96 atoms for the bulk and 12 and 24 atomic layers for the surface slab model. Our results show that for Mn concentrations above 6% there is an increase in the Mn-N bond distance in the c direction, due to the fact that the Mn has an atomic radium greater than that of the Ga and different physical and chemical properties. For the surface calculations, we substituted the Ga for the Mn in different positions relative to the external surface, sub-surface and corre, it was observed that the total energy increased as the Mn atoms moved from the surface layer to the interior sites and when we consider the equilibrium shape based in the thermodynamic stability, the most stable surface energies for the (1010) and (1020) planos of wurtzite GaN are found for the ~8% Mn concentration. When the Mn concentration increases, the band gap decreases for the bulk as well as for the surfaces, the gap being direct for the bulk, except for the 18% concentration, and for the (1010) surface, whereas the gap is found indirect for the (1120) surface for the concentrations 6 and 17%. The analysis of the density... (Complete abstract click electronic access below) / Doutor