Segregation of in to dislocations in InGaN

Dislocations are one-dimensional topological defects that occur frequently in functional thin film materials and that are known to degrade the performance of InxGa1-xN-based optoelectronic devices. Here, we show that large local deviations in alloy composition and atomic structure are expected to occur in and around dislocation cores in InxGa1-xN alloy thin films. We present energy-dispersive X-ray spectroscopy data supporting this result. The methods presented here are also widely applicable for predicting composition fluctuations associated with strain fields in other inorganic functional material thin films

Dislocation core structures in (0001) InGaN

Threading dislocation core structures in c-plane GaN and InxGa1−xN (0.057 ≤ x ≤ 0.20) films were investigated by aberration-corrected scanning transmission electron microscopy. a-type dislocations are unaffected by alloying with indium and have a 5/7-atom ring core structure in both GaN and InxGa1−xN. In contrast, the dissociation lengths of (a + c)-type dislocations are reduced, and new 7/4/9-atom ring and 7/4/8/5-atom ring core structures were observed for the dissociated (a + c)-type dislocations in InxGa1−xN, which is associated with the segregation of indium near (a + c)-type and c-type dislocation cores in InxGa1−xN, consistent with predictions from atomistic Monte Carlo simulations.This work was funded in part by the Cambridge Commonwealth Trust, St. John’s College and the EPSRC (grant number EP/I012591/1). MAM acknowledges support from the Royal Society through a University Research Fellowship. Additional support was provided by the EPSRC (Supplementary data for EPSRC [49] is available) through the UK National Facility for Aberration-Corrected STEM (SuperSTEM). The Titan 80-200kV ChemiSTEM™ was funded through HM Government (UK) and is associated with the capabilities of the University of Manchester Nuclear Manufacturing (NUMAN) capabilities. SJH acknowledges funding from the Defence Threat Reduction Agency (DTRA) USA (grant number HDTRA1-12-1-0013). The authors also acknowledge C. M. McGilvery and A. Kovacs for helpful discussions.This is the author accepted manuscript. It is currently under an indefinite embargo pending publication by AIP

Structure and strain relaxation effects of defects in In<inf>x</inf>Ga<inf>1-x</inf>N epilayers

The formation of trench-defects is observed in 160 nm-thick InxGa1-xN epilayers with x ≤ 0.20, grown on GaN on (0001) sapphire substrates using metalorganic vapour phase epitaxy. The trench-defect density increases with increasing indium content, and high resolution transmission electron microscopy shows an identical structure to those observed previously in InGaN quantum wells, comprising meandering stacking mismatch boundaries connected to an I1-type basal plane stacking fault. These defects do not appear to relieve in-plane compressive strain. Other horizontal sub-interface defects are also observed for these samples and are found to be pre-existing threading dislocations which form half-loops by bending into the basal-plane, and not basal-plane stacking faults, as previously reported by other groups. The origins of these defects are discussed, and are likely to originate from a combination of the small in-plane misorientation of the sapphire substrate and the thermal mismatch strain between the GaN and InGaN layers grown at different temperatures.This work was funded in part by the Cambridge Commonwealth trust and the EPSRC. SKR is funded through the Cambridge-India Partnership Fund and Indian Institute of Technology Bombay via a scholarship. SKR also acknowledges funds from St. John’s College. MAM acknowledges support from the Royal Society through a University Research Fellowship.This is the accepted manuscript version. The final version is available from AIP at http://scitation.aip.org/content/aip/journal/jap/116/10/10.1063/1.4894688

Hot wire chemical vapor processing (HWCVP) - a prospective tool for VLSI

Today the Very Large Scale Industry (VLSI) is looking towards process solutions, which will avoid the problems associated with the conventional or presently employed technologies. This demand has become more intense with the VLSI industry extending their horizons towards Micro electro-mechanical systems (MEMS) based devices and Application-Specific Integrated Circuits ASICs). The areas of concern are development of high-k dielectric thin films, highly conducting polysilicon thin films, ultra thin diffusion barriers on low dielectric constant layers with electromigration resistant metal interconnects. Over the last few years, work carried out on the hot wire chemical vapor process (HWCVP) has shown that, this technique has great potential to yield the desired materials at low processing temperatures. This paper discusses the results we have obtained in the above areas and also the extension of application of this technique to areas like MEMS and ASICs. (c) 2007 Elsevier B.V. All rights reserved

Non-plasma-based technologies to augment backend processing in future ULSI

The solution to the problem of increased resistance-capacitance (RC) delay in the present day ULSI is to use porous low-k dielectric films (k = 2.0) along with Copper interconnects. There are a number of issues with Cu/low-k integration, such as Cu diffusion in the porous low-k film, moisture penetration, and damage during backend processing steps like etching and photoresist ashing. Water vapor is introduced into the low-k layer during ashing of the photo resist, which raises the k value to typically above 3. We have successfully addressed all these issues in the case of hydrogen silsesquioxane (HSQ) (k = 2.8) with the help of a non-plasma-based hot-wire-induced chemical-vapor process (HWCVP). With the help of this process, we have also been successful in developing an ultra-thin hydrogenated amorphous silicon-carbon-based barrier layer that completely avoids copper diffusion and shows a higher resistance to electromigration

Effect of substrate temperature on HWCVD deposited a-SiC : H film

Hydrogenated amorphous silicon carbon (a-SiC:H) films were deposited using pure SiH4 and C2H2 without hydrogen dilution by hot wire chemical vapor deposition (HWCVD) technique. The photoluminescence, optical, and structural properties of these films were systematically studied as a function of substrate temperature (T-s). a-SiC:H films deposited at lower substrate temperature (T-s) show degradation in their structural, optical and network properties. The hydrogen content (C-H) in the films was found to be increased with decrease of T-s studied. Photoluminescence spectra shift to higher energy and less FWHM at high T-s. Raman spectroscopic analysis showed that structural disorder increases with decrease in the T-s. (c) 200

Microscopic properties of H-2 diluted HWCVD deposited a-SiC : H film

Hydrogenated amorphous silicon carbon (a-SiC:H) films were deposited by hot wire chemical vapor deposition. The evolution of microscopic properties like network bonding, disorder, density and chemical composition are studied as a function of H, dilution. The sp(2) and sp(3) carbon Clusters, hydrogen content and the density of the material has significant effect oil the dielectric properties like tile leakage current of M/a-SiC:H/ MIS structures made with both Cu and Al metal electrode. A higher leakage current is observed in the case of Cu electrode. These changes are important for its applicability as a low dielectric constant barrier material in microelectronic devices, (c) 2005 Elsevier B.V. All rights reserved

AMPS-1D simulation studies of electronic transport in n(+)-mu c-Si : H thin films

To study the electronic transport in highly n-doped microcrystalline silicon (n(+)-mu c-Si:H) thin films, grain-boundary trapping model is implemented in AMPS (analysis of microelectronic and photonic structure)-1D. This approach is based on the traditional thermionic-emission model and considering the electronic transport parallel to the substrate. In spite of its simplicity, the model leads to the simulated values of activation energy, free carrier concentration, interface trap charge density and mobility which are in good agreement with the referred Hall effect measurement results for electron cyclotron resonance-chemical vapor deposited (ECR-CVD) highly n-doped mu c-Si:H thin films. (c) 2006 Elsevier B.V. All rights reserved

HYDROGENATED MICROCRYSTALLINE SILICON FILMS PRODUCED AT LOW-TEMPERATURE BY THE HOT-WIRE DEPOSITION METHOD

In this letter we report the synthesis of hydrogenated microcrystalline silicon at low temperature and without hydrogen dilution of the silane gas by the hot wire method. These films are characterized by higher dark conductivity and larger band gap compared to hydrogenated amorphous silicon. Microcrystallinity in these films is clearly established from the sharp crystalline TO-like peak in the first-order Raman spectra. The crystallite size and its volume fraction show a critical dependence on the silane flow rate

From a-C to nanographene by chemical nano-engineering

Interaction of atomic hydrogen with amorphous carbon (a-C) grown on Cu substrate has been explored for the first time. Here we report the investigations performed at 600 degrees C substrate temperature. This research finds its significance in understanding the role of atomic hydrogen in establishing the growth of graphene at low substrate temperatures. After exposing the a-C film to atomic hydrogen for various durations, we observe that atomic hydrogen reacts with the a-C film on Cu surface leading to the formation of nanographene. With the increase in exposure time, graphene nuclei grow in number and dimension, forming a polycrystalline network of nanographene domains. High resolution transmission electron microscope images reveal this structural transformation, which has also been substantiated by Raman spectra. The chemical compositional analysis is performed using X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Based on these observations, we explain the probable mechanism which elucidates the role of atomic hydrogen in transforming a-C into sp(2) hybridized hexagonal structures in the presence of Cu at 600 degrees C. (C) 2018 Elsevier B.V. All rights reserved