Aluminum gallium nitride (AlGa1-xN) films with compositions from x = 0 to x = 0.333 were characterized by cathodoluminescence scanning electron microscopy (CL-SEM), optical microscopy, and photoluminescence (PL). The films were grown by MOCVD on (00.1) oriented sapphire. Two types of large-scale defects were observed both by optical microscopy and by CL-SEM: networks of microcracks along 3-fold symmetry directions, and hexagonal closed-loop defects. The closed-loop defects occur only in the lower-x films, while the microcracks are most prevalent in the higher-x films. Spatially resolved CL spectra taken near these defects show large shifts in the energy of the band-edge emission peak, which are attributed to inhomogeneous stresses. UV-laser-excited PL spectra were obtained from the top surface and bottom surface (film substrate interface) of each film. The PL spectra were compared to CL spectra obtained at several electron energies from 5 to 30 keV. The results of this comparison suggest that defect densities and stresses are larger near the top and bottom surfaces than in the middle of the films. Spectra of the higher-x films show a monotonic decrease of the peak energy with increasing excitation depth, which may arise from a stress gradient in the direction normal to the surface.
Cathodoluminescence (CL) image and spectra of undoped GaN epilayers grown by LP-MOVPE on (0001) -AIO have been studied. The x-ray data are measured by using the -mode (open and narrow window) and the 2/-mode. The samples have two kinds of morphologies: sample A has large hexagonal crystalline structure, sample B has mirror-like surface with very smaller grain boundaries. The superposition rule, = + , holds roughly in the samples, where is FWHM in conventional rocking curve, represents misorientations of the GaN grains, represents variation of the lattice spacing. We found that the is about one order of magnitude smaller than in the sample B. The value of / of the sample B is larger than that of the sample A. CL spectra show near band-edge luminescence and yellow luminescence (YL). Inhomogeneous light emission has been observed in samples A and B. In the CL image of sample A, we found two kinds of YL image shape: hexagonal shaped broad emission and fine straight line shaped emission that has triple symmetry. The former is associated with hexagonal grain boundaries. The light emission spreads around the grain boundaries. The latter is associated with cracks. The YL is very confined along the cracks. The relationship of CL and x-ray data of the samples has been studied. We consider that the YL seems to be related to mosaic structure. The comparison of the two kinds of samples and the origin of YL will be discussed in detail.
Siemens Solid Edge 2020 Crack With Product Key
Download: https://miimms.com/2vBZV6
Nickel has been used in Au-Ni ohmic contacts to p-type GaN and has also been examined as a Schottky barrier to n-type GaN. Knowledge of the metallurgy of the Ni/GaN system will contribute to a better understanding of these contacts and may aid in improving them. In this study, metallurgical reactions between Ni and GaN have been explored at various temperatures between 400 and 900C in N, Ar, and forming gas. Glancing angle x-ray diffraction and Auger depth profiling were employed to determine the extent of interdiffusion between Ni and GaN and identify the phases that form upon annealing. No reaction was observed between Ni and GaN upon annealing in N or in forming gas (N + H) at 400C for 10 minutes. A Ni-Ga solid solution was observed to form at 600C after 1 hour, with the extent of dissolution increasing with continued annealing. After annealing at 750C for 1 hour, Ni or Ar, greater intermixing occurred. The reaction product was either NiGa or fcc Ni with dissolved Ga. Annealing at 900C resulted in the formation of NiGa with release of N to the atmosphere, even when annealing in N gas. Thus, a trend of increasing Ga content in the reacted films was observed with increasing temperature, while the formation of nickel nitrides was not observed. The observed reactions are consistent with the thermodynamics phase of the Ni-Ga-N system.
An ambient temperature stable precursor with formula corresponding to gallium imide, , was obtained from the reactions between [Ga(NMe)] and liquid or gaseous NH. The pyrolysis of this solid at temperatures between 210 and 600C under vacuum or, preferably, under an NH atmosphere, yielded grayish to yellow materials which were shown by XRD anal TEM to be the rare cubic/hexagonal form of GaN. Variations in the processing parameters enabled some control over GaN particle growth in the average diameter range from one to several nanometers. In another approach, the combination of LiGaH and NHBr in EtO resulted in the isolation of a precursor which appeared to be a gallazane with empirical formula HGaNH. This solid, after pyrolysis at 600C under vacuum or an NH atmosphere, was converted to yellow products that were shown to be nanocrystalline particles of cubic/hexagonal GaN. Specific variations in the pyrolysis conditions yielded cubic GaN as determined from an XRD powder pattern. These nanophase GaN materials have also been characterized by room temperature photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies. In general, band-edge PL is not observed for these samples, but rather yellow-green defect emission centered near 2.3 eV. Measurements acquired to date suggest that the differences in the relative quantum efficiencies between samples are a function of thermolysis temperature and the presence of ammonia during semiconductor preparation, i.e., when higher annealing temperatures are employed and NH is utilized, this yellow PL is quenched considerably. Interestingly, the PLE spectra of the strongly-emitting samples exhibit a sharp peak near 3.9 eV, shifted 0.3 eV from the bulk gap value of GaN. 2ff7e9595c
Comentários