Abstract: Non-polar a-plane AlGaN epilayers of high structural quality have been grown on r-sapphire substrate by using metalorganic chemical vapor deposition (MOCVD). A graded non-polar AlGaN buffer layer with variable aluminium concentration was used to improve the structural quality of the non-polar a-plane AlGaN epilayer. The characterisations were carried out by high-resolution X-ray diffraction (HR-XRD), atomic force microscopy (AFM) and Hall effect measurement. The XRD and AFM results demonstrate that the Al-composition-graded non-polar AlGaN buffer layer significantly improved the crystalline quality and the surface morphology of the top layer. A low root mean square roughness 1.52 nm is obtained from AFM, and relatively low background carrier concentration down to 3.9× cm-3 is obtained from Hall effect measurement.
Abstract: In this paper, an experimental and theoretical study of the processes of mesoporous silicon carbonization during the formation of buffer layers for the subsequent epitaxy of 3C-SiC films and related wide-band-gap semiconductors is performed. Experimental samples were obtained by the method of chemical vapor deposition and investigated by scanning electron microscopy. Analytic expressions were obtained for the effective diffusion factor and carbon atoms diffusion length in a porous system. The proposed model takes into account the processes of Knudsen diffusion, coagulation and overgrowing of pores during the formation of a silicon carbide layer.
Abstract: Optical properties of sputter-deposited ZnS thin films
were investigated as potential replacements for CBD(chemical bath
deposition) CdS buffer layers in the application of CIGS solar cells.
ZnS thin films were fabricated on glass substrates at RT, 150oC, 200oC,
and 250oC with 50 sccm Ar gas using an RF magnetron sputtering
system. The crystal structure of the thin film is found to be zinc blende
(cubic) structure. Lattice parameter of ZnS is slightly larger than CdS
on the plane and thus better matched with that of CIGS. Within a
400-800 nm wavelength region, the average transmittance was larger
than 75%. When the deposition temperature of the thin film was
increased, the blue shift phenomenon was enhanced. Band gap energy
of the ZnS thin film tended to increase as the deposition temperature
increased. ZnS thin film is a promising material system for the CIGS
buffer layer, in terms of ease of processing, low cost, environmental
friendliness, higher transparency, and electrical properties
Abstract: Vickers indentation is used to measure the hardness
of materials. In this study, numerical simulation of Vickers
indentation experiment was performed for Diamond like Carbon
(DLC) coated materials. DLC coatings were deposited on stainless
steel 304 substrates with Chromium buffer layer using RF Magnetron
and T-shape Filtered Cathodic Vacuum Arc Dual system The
objective of this research is to understand the elastic plastic
properties, stress strain distribution, ring and lateral crack growth and
propagation, penetration depth of indenter and delamination of
coating from substrate with effect of buffer layer thickness. The
effect of Poisson-s ratio of DLC coating was also analyzed. Indenter
penetration is more in coated materials with thin buffer layer as
compared to thicker one, under same conditions. Similarly, the
specimens with thinner buffer layer failed quickly due to high
residual stress as compared to the coated materials with reasonable
thickness of 200nm buffer layer. The simulation results suggested the
optimized thickness of 200 nm among the prepared specimens for
durable and long service.