Evolution of structural defects in SiOx films fabricated by electron cyclotron resonance plasma chemical vapour deposition upon annealing treatment

We study the structural defects in the SiOx film prepared by electron cyclotron resonance plasma chemical vapour deposition and annealing recovery evolution. The photoluminescence property is observed in the as-deposited and annealed samples. [-SiO3](2-) defects are the luminescence centres of the ultraviolet photoluminescence (PL) from the Fourier transform infrared spectroscopy and PL measurements. [-SiO3](2-) is observed by positron annihilation spectroscopy, and this defect can make the S parameters increase. After 1000 degrees C annealing, [-SiO3](2-) defects still exist in the films.

Two-dimensional simulation of high-order laterally-coupled GaAs-AlGaAs DFB laser diodes

Laterally-coupled distributed feedback (LC-DFB) laser diodes made without an epitaxial re-growth process have the advantage of a simple fabrication process. In this paper, two-dimensional optical field distribution of the fundamental quasi TE (transverse electric) mode is calculated by means of a semivectorial finite-difference method (SV-FDM). The dependence of the effective coupling coefficient (kappa(eff)) on the dutycycle of first-, second- and third-order LC-DFB LDs is investigated using modified coupled wave equations.

Effect of metal contact's reflection on the effective coupling coefficient of second-order DFB laser diodes

For a second-order DFB-LD, the presence of a metal contact layer can reduce I-st-order radiation. Part of the reflected power is redistributed into guided modes and results in a variation of the effective coupling coefficient kappa(eff). In this paper, we study the effect of the Au top contact's reflection on the kappa(eff) of 2(nd)-order DFB lasers. (C) 2004 Wiley Periodicals, Inc.

Microstructural and compositional characteristics of GaN films grown on a ZnO-buffered Si(111) wafer

Polycrystalline GaN thin films have been deposited epitaxially on a ZnO-buffered (111)-oriented Si substrate by molecular beam epitaxy. The microstructural and compositional characteristics of the films were studied by analytical transmission electron microscopy (TEM). A SiO2 amorphous layer about 3.5 nm in thickness between the Si/ZnO interface has been identified by means of spatially resolved electron energy loss spectroscopy. Cross-sectional and plan-view TEM investigations reveal (GaN/ZnO/SiO2/Si) layers exhibiting definite a crystallographic relationship: [111](Si)//[111](ZnO)//[0001](GaN) along the epitaxy direction. GaN films are polycrystalline with nanoscale grains (similar to100 nm in size) grown along [0001] direction with about 20degrees between the (1 (1) over bar 00) planes of adjacent grains. A three-dimensional growth mode for the buffer layer and the film is proposed to explain the formation of the as-grown polycrystalline GaN films and the functionality of the buffer layer. (C) 2004 Elsevier Ltd. All rights reserved.

Performance analysis of very-small-aperture lasers

The fabrication of very-small-aperture lasers is demonstrated, and their performance is analyzed. Because of strong optical feedback caused by a gold film on the front facet of the laser, its behavior changes: The threshold current decreases, the density of light inside the laser diode and the redshift effect of the spectra are enhanced, and the laser diode's lifetime is shorter than that of common laser diodes with large driving current. (c) 2005 Optical Society of America

mc-Si : H/c-Si solar cell prepared by PECVD

Hetero-junction solar cells with an me-Si: H window layer were achieved. The open voltage is increased while short current is decreased with increasing the mc-Si:H layer's thickness of emitter layer. The highest of V-oc of 597 mV has obtained. When fixed the thickness of 30 nm, changing the N type from amorphous silicon layer to micro-crystalline layer, the efficiency of the hetero-junction solar cells is increased. Although the hydrogen etching before deposition enables the c-Si substrates to become rough by AFM images, it enhances the formation of epitaxial-like micro-crystalline silicon and better parameters of solar cell can be obtained by implying this process. The best result of efficiency is 13.86% with the V-oc of 549.8 mV, J(sc) of 32.19 mA center dot cm(-2) and the cell's area of 1 cm(2).

Effect of lightly Si doping on the minority carrier diffusion length in n-type GaN films

We investigate the effects of lightly Si doping on the minority carrier diffusion length in n-type GaN films by analyzing photovoltaic spectra and positron annihilation measurements. We find that the minority carrier diffusion length in undoped n-type GaN is much larger than in lightly Si-doped GaN. Positron annihilation analysis demonstrates that the concentration of Ga vacancies is much higher in lightly Si-doped GaN and suggests that the Ga vacancies instead of dislocations are responsible for the smaller minority carrier diffusion length in the investigated Si-doped GaN samples due to the effects of deep level defects. (c) 2006 American Institute of Physics.

Effect of a low-temperature thin buffer layer on the strain accommodation of In0.25Ga0.75As grown on a GaAs(001) substrate

Various low-temperature (LT) ultra-thin buffer layers have been fabricated on the GaAs (001) substrate. The buffer layer is decoupled from the host substrate by introducing low-temperature defects. The 400 nm In0.25Ga0.75As films were grown on these substrates to test the 'compliant' effects of the buffer layers. Atomic force microscopy, photoluminescence, double crystal x-ray diffraction and transmission electron microscopy were used to estimate the quality of the ln(0.25)Ga(0.75)As layer. The measurements indicated that the misfit strains in the epilayer can be accommodated by the LT ultra-thin buffer layer. The strain accommodation effects of the LT defects have been discussed in detail.

Strain accommodation of 3C-SiC grown on hydrogen-implanted Si (001) substrate

The hydrogen-implanted Si substrate has been used for the fabrication of the "compliant substrate", which can accommodate the mismatch strain during the heteroepitaxy. The compliance of the substrate can be modulated by the energy and dose of implanted hydrogen. In addition, the defects caused by implantation act as the gettering center for the internal gettering of the harmful metallic impurities. Compared with SiC films growth on substrate without implantation. all the measurements indicated that the mismatch strains in the SiC films grown on this substrate have been released and the crystalline qualities have been improved. It is a practical technique used for the compliant substrate fabrication and compatible with the semiconductor industry. (C) 2003 Elsevier B.V. All rights reserved.

Study on pollution for the photoelectronic material InP

The mass spectrum analysis of crystal face (100) and (111) and the photoluminescence analysis of crystal face (100) in the photoelectronic material InP were given. The Hall coefficient, charge carrier concentration and Hall mobility were determined. Experimental results indicate that the pollution of silicon is predominant.

Metalorganic chemical vapor deposition of GaNAs alloys using different Ga precursors

The GaNAs alloys have been grown by metalorganic chemical vapor deposition (MOCVD) using dimethylhydrazine (DMHv) as the nitrogen precursor, triethylgallium (TEGa) and trimethylgallium (TMGa) as the gallium precursors, respectively. Both symmetric (004) and asymmetric (1 1 5) high-resolution X-ray diffraction (HRXRD) were used to determine the nitrogen content in GaNAs layers. Secondary ion mass spectrometry (SIMS) was used to obtain the impurity content. T e influence of different Ga precursors on GaNAs quality has been investigated. Phase separation is observed in the < 1 1 5 > direction when using TMGa as the Ga precursor but not observed when using TEGa. This phenomenon should originate from the parasitic reaction between the Ga and N precursors. Furthermore. samples grown with TEGa have better quality and less impurity contamination than those with TMGa. Nitrogen content of 5.742% has been achieved using TEGa and no phase separation observed in the sample. (C) 2002 Elsevier Science B.V. All rights reserved.

Nanofabrication of grid-patterned substrate by holographic lithography

The two-dimensional grid patterns on Si(001) in nanometer scale have been fabricated by holographic lithography and reactive ion etching, which can be used as a substrate for positioning Ge islands during self-assembled epitaxy to obtain an ordered Ge quantum dots matrix. By changing the configuration of the holographic lithography and the etching rate and time, we can control the grid period, the shape of the pattern cell, and the orientation of those shapes, respectively. (C) 2002 Elsevier Science B.V. All rights reserved.

A Raman scattering study of GaAs: As films lifted off GaAs substrate

We performed Raman scattering investigations on low-temperature-grown (LTG) films of GaAs that had been lifted off the GaAs substrate. The Raman measurements unambiguously show the effects of excess arsenic on phonon scattering from LTG films of GaAs. The larger downwards shift of the LO phonon frequency for unannealed free-standing films is explained by invoking the elimination of mismatch strain. The Raman signal due to precipitates of elemental arsenic in the annealed GaAs : As films is determined. It is confirmed that the arsenic clusters formed by rapid thermal annealing are mainly amorphous, giving rise a broad Raman peak in the range 180-260 cm(-1).

Photoluminescence enhancement of porous silicon by organic cyano compounds

A pronounced photoluminescence enhancement on chemically oxidized porous silicon was induced by a series of organic cyano compounds including 1,2-dicyanoethylene (CE), 1,3-dicyanobenzene (1,3-CB), 1,4-dicyanobenzene (1,4-CB), 1-cyanonaphthalene (1-CN), and 9-cyanoanthracene (9-CA). Photoluminescence enhancement effects were reversible for all compounds studies in this work. A dependence of photoluminescence enhancement on the steric effect and the electronic characteristics of these compounds and the structure of the porous silicon substrates were analyzed in terms of the photoluminescence enhancing factors. Surface chemical composition examined by Fourier transform infrared (FTIR) spectra demonstrated that the surface Si-H bonds were not changed and no new luminescent compounds were formed on porous silicon surface during adsorption of cyano compounds. A mechanism based on induced surface states acting as radiative recombination centers by cyano compounds adsorption was suggested.