Structural properties of single-phase films of κ-In 2 Se 3 and γ-In 2 Se 3 were investigated.Both films were polycrystalline but their microstructure differed considerably. The alattice parameter of κ-In 2 Se 3 has been measured. Comparison between these two materials indicates that κ-In 2 Se 3 has a significantly larger unit cell (∆c = 2.5 ± 0.2 % and ∆a = 13.5 ± 0.5 %) and a structure more similar to the α-phase of In 2 Se 3 . a)

The availability of reliable and quick methods to determine defect density and polarity in GaN films is of great interest. We have used photo-electrochemical (PEC) and hot wet etching using H 3 PO 4 and molten KOH to estimate the defect density in GaN films grown by hydride vapor phase epitaxy (HVPE) and molecular beam epitaxy (MBE). Free-standing whiskers and hexagonal etch pits are formed by PEC and wet etching respectively. Using Atomic Force Microscopy (AFM), we found the whisker density to be similar to etch pit densities for samples etched under precise conditions. densities obtained by etching which increased our confidence in the consistency of methods used. Additionally Transmission Electron Microscopy (TEM) observations confirmed dislocation Hot wet etching was used also to investigate the polarity of GaN films together with ConvergentBeam Electron Diffraction (CBED) and AFM imaging. We found that hot H 3 PO 4 etches N-polarity GaN films very quickly resulting in the complete removal or drastic change of surface morphology as revealed by AFM or optical microscopy. On the contrary, the acid attacks only defect sites in Gapolarity films producing nanometer-scale pits but leaving the defect-free GaN intact and the morphology unchanged. Additionally, the polarity assignments were related to the as-grown morphology and to the growth conditions of the buffer layer and the subsequent GaN layer.

A free-standing GaN template grown to a thickness of 300 µm by hydride vapor phase epitaxy (HVPE) has been characterized for its structural properties by transmission electron microscopy (TEM). The TEM investigation was augmented by X-ray diffraction, defect delineation etching process followed by imaging with atomic force microscopy (AFM), and variable temperature photoluminescence (PL). Convergent Beam Electron Diffraction (CBED) was employed to determine the polarity of the free surface and the side juxtaposed to substrate before separation. The substrates side was confirmed to the N-face indicating a growth in the [0001] direction from Ga to N. The density of dislocations near the N-face was determined to be, in order, 3 ± 1 x 10 7 , 4 ± 1 x 10 7 , and about 1 x 10 7 cm -2 as determined by cross-sectional TEM, plan-view TEM and a defect revealing etch, respectively. Identical observations on the Ga-face revealed the defect concentration to be, in order, less than 1 x 10 7 cm -2 by plan-view TEM, 5 x 10 5 cm -2 by cross-sectional TEM, and 5 x 10 5 cm -2 by defect revealing hot H 3 PO 4 acid, respectively. The full width at half maximum (FWHM) of the symmetric (0002) X-ray diffraction peak was 69 and 160 arcsec for the Ga and N-faces, respectively. That for the asymmetric (1014) peak was 103 and 140 arcsec for Ga-and N-faces, respectively. The donor bound exciton linewidth as measured on the Ga and N-face (after the removal of the damage) is about 1 meV each at 10K. Instead of the commonly observed yellow band, this sample displayed a green band, which is centered at about 2.44 eV.

Characterization of stoichiometric surface and buried SiN films fabricated by ion implantation using extended xray absorption fine structure