Determination of a misfit dislocation complex in SiGe/Si heterostructures by image deconvolution technique in HREM

The core structure of a dislocation complex in SiGe/Si system composed of a perfect 60degrees dislocation and an extended 60 dislocation has been revealed at atomic level. This is attained by applying the image deconvolution technique in combination with dynamical diffraction effect correction to an image taken with a 200 kV field-emission high-resolution electron microscope. The possible configuration of the dislocation complex is analyzed and their Burgers vectors are determined. (C) 2003 Elsevier B.V. All rights reserved.

Enhanced optical properties of the GaAsN/GaAs quantum-well structure by the insertion of InAs monolayers

Microstructural and optical properties of InAs-inserted and reference single GaAsN/GaAs quantum-well (QW) structures grown by metalorganic chemical vapor deposition were investigated using cross-sectional transmission electron microscopy and photoluminescence (PL). Significant enhancement of PL intensity and a blueshift of PL emission were observed from the InAs-inserted GaAsN/GaAs QW structure, compared with the single GaAsN/GaAs QW structure. Strain compensation and In-induced reduction of N incorporation are suggested to be two major factors affecting the optical properties. (C) 2004 American Institute of Physics.

Growth mechanism of truncated triangular GaAs nanowires

During the growth of GaAs nanowires on the {111}B GaAs substrate, truncated triangular GaAs nanowires were commonly observed in the bottom region of nanowires. Through detailed structural analysis by electron microscopy, we have determined the growth mechanism of truncated triangular GaAs nanowires.

Optical autocorrelator that uses a surface-emitting second-harmonic generator on (211)B GaAs

An optical autocorrelator grown on a (211)B GaAs substrate that uses visible surface-emitted second-harmonic generation is demonstrated. The (211)B orientation needs TE mode excitation only, thus eliminating the problem of the beating between the TE and TM modes that is required for (100)-grown devices; it also has the advantage of giving higher upconversion efficiency than (111) growth. Values of waveguide loss and the difference in the effective refractive index between the TE(0) and TE(1) modes were also obtained from the autocorrelation experiment.

Computer simulation of radio-frequency methane/hydrogen plasmas and their interaction with GaAs Surfaces

The following thesis describes the computer modelling of radio frequency capacitively coupled methane/hydrogen plasmas and the consequences for the reactive ion etching of (100) GaAs surfaces. In addition a range of etching experiments was undertaken over a matrix of pressure, power and methane concentration. The resulting surfaces were investigated using X-ray photoelectron spectroscopy and the results were discussed in terms of physical and chemical models of particle/surface interactions in addition to the predictions for energies, angles and relative fluxes to the substrate of the various plasma species. The model consisted of a Monte Carlo code which followed electrons and ions through the plasma and sheath potentials whilst taking account of collisions with background neutral gas molecules. The ionisation profile output from the electron module was used as input for the ionic module. Momentum scattering interactions of ions with gas molecules were investigated via different models and compared against results given by quantum mechanical code. The interactions were treated as central potential scattering events and the resulting neutral cascades were followed. The resulting predictions for ion energies at the cathode compared well to experimental ion energy distributions and this verified the particular form of the electrical potentials used and their applicability in the particular geometry plasma cell used in the etching experiments. The final code was used to investigate the effect of external plasma parameters on the mass distribution, energy and angles of all species impingent on the electrodes. Comparisons of electron energies in the plasma also agreed favourably with measurements made using a Langmuir electric probe. The surface analysis showed the surfaces all to be depleted in arsenic due to its preferential removal and the resultant Ga:As ratio in the surface was found to be directly linked to the etch rate. The etch rate was determined by the methane flux which was predicted by the code.

Surface:plasma interactions in GaAs subjected to capacitively coupled RF plasmas

Surface compositional changes in GaAs due to RF plasmas of different gases have been investigated by XPS and etch rates were measured using AFM. Angular Resolved XPS (ARXPS) was also employed for depth analysis of the composition of the surface layers. An important role in this study was determination of oxide thickness using XPS data. The study of surface - plasma interaction was undertaken by correlating results of surface analysis with plasma diagnosis. Different experiments were designed to accurately measure the BEs associated with the Ga 3d, Ga 2P3/2 and LMM peaks using XPS analysis and propose identification in terms of the oxides of GaAs. Along with GaAs wafers, some reference compounds such as metallic Ga and Ga2O3 powder were used. A separate study aiming the identification of the GaAs surface oxides formed on the GaAs surface during and after plasma processing was undertaken. Surface compositional changes after plasma treatment, prior to surface analysis are considered, with particular reference to the oxides formed in the air on the activated surface. Samples exposed to ambient air for different periods of time and also to pure oxygen were analysed. Models of surface processes were proposed for explanation of the stoichiometry changes observed with the inert and reactive plasmas used. In order to help with the understanding of the mechanisms responsible for surface effects during plasma treatment, computer simulation using SRIM code was also undertaken. Based on simulation and experimental results, models of surface phenomena are proposed. Discussion of the experimental and simulated results is made in accordance with current theories and published results of different authors. The experimental errors introduced by impurities and also by data acquisition and processing are also evaluated.

Faster radial strain relaxation in InAs-GaAs core-shell heterowires

The structure of wurtzite and zinc blende InAs-GaAs (001) core-shell nanowires grown by molecular beam epitaxy on GaAs (001) substrates has been investigated by transmission electron microscopy. Heterowires with InAs core radii exceeding 11 nm, strain relax through the generation of misfit dislocations, given a GaAs shell thickness greater than 2.5 nm. Strain relaxation is larger in radial directions than axial, particularly for shell thicknesses greater than 5.0 nm, consistent with molecular statics calculations that predict a large shear stress concentration at each interface corner. © 2012 American Institute of Physics.

Cracking in hydrogen ion-implanted Si/Si0.8Ge0.2/Si heterostructures

We demonstrate that a controllable cracking can be realized in Si with a buried strain layer when hydrogen is introduced using traditional H-ion implantation techniques. However, H stimulated cracking is dependent on H projected ranges; cracking occurs along a Si0.8Ge0.2 strain layer only if the H projected range is shallower than the depth of the strained layer. The absence of cracking for H ranges deeper than the strain layer is attributed to ion-irradiation induced strain relaxation, which is confirmed by Rutherford-backscattering-spectrometry channeling angular scans. The study reveals the importance of strain in initializing continuous cracking with extremely low H concentrations.

Optical autocorrelator that uses a surface-emitting second-harmonic generator on (211)B GaAs

An optical autocorrelator grown on a (211)B GaAs substrate that uses visible surface-emitted second-harmonic generation is demonstrated. The (211)B orientation needs TE mode excitation only, thus eliminating the problem of the beating between the TE and TM modes that is required for (100)-grown devices; it also has the advantage of giving higher upconversion efficiency than (111) growth. Values of waveguide loss and the difference in the effective refractive index between the TE(0) and TE(1) modes were also obtained from the autocorrelation experiment.

202nm continuous tuning from high-power external-cavity InAs/GaAs quantum-dot laser

Record broadly tunable high-power external cavity InAs/GaAs quantum-dot diode laser is demonstrated. A maximum output power of 455mW and a side-mode suppression ratio >45dB in the central part of the tuning range are achieved. ©2010 IEEE.

SHG in a low-loss orientation patterned GaAs waveguide

We demonstrate second harmonic generation at 1621 nm in a low-loss orientation-patterned GaAs waveguide pumped by an optical parametric oscillator system. The losses were estimated to be 2.12 dB/cm.

Broadly tunable high-power InAs/GaAs quantum-dot external cavity diode lasers

A record broadly tunable high-power external cavity InAs/GaAs quantum-dot diode laser with a tuning range of 202 nm (1122 nm-1324 nm) is demonstrated. A maximum output power of 480 mW and a side-mode suppression ratio greater than 45 dB are achieved in the central part of the tuning range. We exploit a number of strategies for enhancing the tuning range of external cavity quantum-dot lasers. Different waveguide designs, laser configurations and operation conditions (pump current and temperature) are investigated for optimization of output power and tunability. (C) 2010 Optical Society of America

Second harmonic generation in a low-loss orientation-patterned GaAs waveguide

The technology of low-loss orientation-patterned gallium arsenide (OP-GaAs) waveguided crystals was developed and realized by reduction of diffraction scattering on the waveguide pattern. The propagation losses in the OP-GaAs waveguide were estimated to be as low as 2.1 dB/cm, thus demonstrating the efficient second harmonic generation at 1621 nm under an external pumping. © 2013 Optical Society of America.

Continuous wave terahertz radiation from an InAs/GaAs quantum-dot photomixer device

Generation of continuous wave radiation at terahertz (THz) frequencies from a heterodyne source based on quantum-dot (QD) semiconductor materials is reported. The source comprises an active region characterised by multiple alternating photoconductive and QD carrier trapping layers and is pumped by two infrared optical signals with slightly offset wavelengths, allowing photoconductive device switching at the signals? difference frequency ~1 THz.(C) 2012 American Institute of Physics.