Effect of critical thickness on structural and optical properties of InxGa1-xN/GaN multiple quantum wells

InGaN/GaN multiquantum-well (MQW) structures grown by metalorganic chemical-vapor deposition on n-type GaN and capped by p-type GaN were investigated by cross-sectional transmission electron microscopy, double crystal x-ray diffraction, and temperature-dependent photoluminescence. For the sample with strained-layer thicknesses greater than the critical thicknesses, a high density of pure edge type threading dislocations generated from MQW layers and extended to the cap layer was observed. These dislocations result from a relaxation of the strained layers when their thicknesses are beyond the critical thicknesses. Because of indium outdiffusion from the well layers due to the anneal effect of Mg-doped cap layer growth and defects generated from strain relaxation, the PL emission peak was almost depressed by the broad yellow band with an intensity maximum at 2.28 eV. But for the sample with strained-layer thicknesses less than the critical thicknesses, it has no such phenomenon. The measured critical thicknesses are consistent with the calculated values using the model proposed by Fischer, Kuhne, and Richter. (C) 2004 American Institute of Physics.

Characteristics of oxide-free InGaAlAs layers grown by narrow stripe selective MOVPE

Narrow stripe selective MOVPE has been used to grow high quality oxide-free InGaAlAs layers on an InP substrate patterned with SiO2 masks at optimized growth conditions. Mirror-like surface morphologies and abrupt cross sections are obtained in all samples without spike growth at the mask edge. For the narrow stripe selectively grown InGaAlAs layers with a mesa width of about 1.2 mu m, a bandgap wavelength shift of 70 nm, a photoluminescence (PL) intensity of more than 80% and a PL full width at half maximum (FWHM) of less than 60 meV are obtained simultaneously with a small mask width variation from 0 to 40 mu m. The characteristics of the thickness enhancement ratio and the PL spectrum dependence on the mask width are presented and explained by considering both the migration effect from a masked region and the lateral vapour diffusion effect.

Influence of rapid thermal annealing on InAs/InAlAs/InP quantum wires with different InAs deposited thickness

We have studied the effect of the post-growth rapid thermal annealing on optical and electrical properties of InAs/InAlAs/InP quantum wires with various InAs deposited thickness. Quite different annealing behaviors in photoluminescence and dark resistance are observed, which can be attributed to dislocations in samples. After annealing at 800 degrees C, quantum wires still exist in the sample with two monolayer InAs deposited thickness, but the temperature-dependent PL properties are changed greatly due to the intermixing of In/Al atoms. (c) 2005 Elsevier B.V. All rights reserved.

Silicon membrane resonant-cavity-enhanced photodetector

A Si resonant-cavity-enhanced (RCE) photodiode was fabricated on a silicon membrane. The Si membrane was formed by etching from the back side of the silicon-on-insulator substrate with the buried SiO2 layer as etch-stop layer. A gold layer was deposited serving as an electrode layer and bottom mirror of the RCE photodiode. The photodiode had an external quantum efficiency of 33.8% at the resonant wavelength of 848 nm and a full width at half maximum (FWHM) of 17 nm. The responsivity was 4.6 times that of a conventional Si p-i-n photodiode with the same absorption layer thickness. (c) 2005 American Institute of Physics.

Growth and properties of GaN on Si (111) substrates with AlGaN/AlN buffer layer by NH3-GSMBE

We describe the growth of GaN on Si (111) substrates with a AlGaN/AlN buffer layer by NH3-GSMBE. The influence of the AlN and AlGaN buffer layer thickness on the crack density of GaN has been investigated. It is found that the optimum thickness is 120 nm and 250 nm for AlN and AlGaN layers, respectively. The full width at half maximum of the GaN (0002) peak in the triple-crystal x-ray rocking curve measurement is about 15 arcmin.

Epitaxial SiC grown on silicon-on-insulator substrate with ultra-thin silicon-over-layer

We report on the comparative studies of epitaxial SiC films grown on silicon-on-insulator (SOI) and Si bulk substrates. The silicon-over-layer (SOL) on the SOI has been thinned down to different thicknesses, with the thinnest about 10 nm. It has been found that the full-width-at-half-maxim in the X-ray diffraction spectrum from the SiC films decreases as the SOL thickness decreases, indicating improved quality of the SiC film. A similar trend has also been found in the Raman spectrum. One of the potential explanations for the observation is strain accommodation by the ultra-thin SOI substrate. (c) 2005 Elsevier B.V. All rights reserved.

Room temperature 1.25 mu m emission from high indium content InxGa1-xAs/GaAs quantum wells grown by molecular beam epitaxy

Long-wavelength high indium content InxGa1-xAs/GaAs single/multi quantum wells (QWs) structures have been successfully grown by molecular beam epitaxy. It is evidenced by X-ray measurements that the critical thickness of the well width of InxGa1-xAs/GaAs QWs with an indium content x of 47.5% can be raised up to 7nm without strain relation. 1.25μ m photoluminescence (PL) emission is obtained from the QWs with narrower full-width at half maximum (FWHM) less than 30meV. Our results are important basements which are useful for further fabricating GaAs-based long-wavelength devices. © 2005 Elsevier B.V. All rights reserved.

An improved TM method for full two-port calibration of the asymmetric test fixtures

Three known standards, including at least one transmission standard, are normally required for the full two-port calibration of test fixtures. Based on the triple-through method, a new general-purpose calibration procedure using only one known reflection standard is proposed in this paper. The experimental results show that our method call provide a simple and accurate approach to fall two-port calibration of the asymmetric test fixtures. (c) 2005 Wiley Periodicals, Inc.

Comparison of the properties of GaN grown on complex Si-based structures

With the aim of investigating the possible integration of optoelectronic devices, epitaxial GaN layers have been grown on Si(Ill) semiconductor-on-insulator (SOI) and on Si/CoSi2/Si(111) using metalorganic chemical vapor deposition. The samples are found to possess a highly oriented wurtzite structure, a uniform thickness, and abrupt interfaces. The epitaxial orientation is determined as GaN(0001)//Si(111), GaN[1120]//Si[110], and GaN[1010]//Si[112], and the GaN layer is tensilely strained in the direction parallel to the interface. According to Rutherford backscattering/channeling spectrometry and (0002) rocking curves, the crystalline quality of GaN on Si(111) SOI is better than that of GaN on silicide. Room-temperature photoluminescence of GaN/SOI reveals a strong near-band-edge emission at 368 nm (3.37 eV) with a full width at half-maximum of 59 meV. (c) 2005 American Institute of Physics.

Effect of layer thickness of immiscible alloy In0.52Al0.48As on the morphology of InAs nanostructure grown on In0.52Al0.48As/InP(001)

Thickness effect of immiscible alloy InAlAs as matrix layer on the morphology of InAs nanostructure grown on InAlAs/InP (0 0 1) by solid-source molecular-beam epitaxy has been studied. Experiments demonstrate that InAs nanostructure grown on thin InAlAs matrix layer forms randomly distributed quantum dot, whereas, grown on thick InAlAs matrix layer forms one-dimension ordered mixture of quantum wire and quantum dot. This drastic modification in the nanostructure morphology is attributed to the generation of composition modulation in the immiscible InAlAs alloy with the increase of the layer thickness. (C) 2004 Elsevier B.V. All rights reserved.

Full counting statistics of transport through two-channel Coulomb blockade systems

A mesoscopic Coulomb blockade system with two transport channels is studied in terms of full counting statistics. It is found that the shot noise and skewness are crucially affected by the quantum mechanical interference. In particular, the super-Poisson behavior can be induced as a consequence of constructive interference, and can be understood by the formation of effective fast-and-slow transport channels. Dephasing and finite temperature effects are carried out together with physical interpretations.

Influence of InAs deposition. thickness on the structural and optical properties of InAs quantum wires

The influence of InAs deposition thickness on the structural and optical properties of InAs/InAlAs quantum wires (QWR) superlattices (SLS) was studied. The transmission electron microscopy (TEM) results show that with increasing the InAs deposited thickness, the size uniformity and spatial ordering of InAs QWR SLS was greatly improved, but threading dislocations initiated from InAs nanowires for the sample with 6 monolayers (MLs) InAs deposition. In addition, the zig-zag features along the extending direction and lateral interlink of InAs nanowires were also observed. The InAs nanowires, especially for the first period, were laterally compact. These structural features may result in easy tunneling and coupling of charge carriers between InAs nanowires and will hamper their device applications to some extent. Some suggestions are put forward for further improving the uniformity of the stacked InAs QWRs, and for suppressing the formation of the threading dislocations in InAs QWR SLS.

Influence of AlN thickness on strain evolution of GaN layer grown on high-temperature AlN interlayer

The strain evolution of a GaN layer grown on a high- temperature AlN interlayer with varying AlN thickness by metalorganic chemical vapour deposition is investigated. In the growth process, the growth strain changes from compression to tension in the top GaN layer, and the thickness at which the compressive- to- tensile strain transition takes place is strongly influenced by the thickness of the AlN interlayer. It is confirmed from the x- ray diffraction results that the AlN interlayer has a remarkable effect on introducing relative compressive strain to the top GaN layer. The strain transition process during the growth of the top GaN layer can be explained by the threading dislocation inclination in the top GaN layer. Adjusting the AlN interlayer thickness could change the density of the threading dislocations in the top GaN layer and then change the stress evolution during the top GaN layer's growth.

The effects of LT AlN buffer thickness on the optical properties of AlGaN grown by MOCVD and Al composition inhomogeneity analysis

We have investigated the growth of AlGaN epilayers on a sapphire substrate by metalorganic chemical vapour deposition using various low-temperature ( LT) AlN buffer thicknesses. Combined scanning electron microscopy and cathodoluminescence investigations reveal the correlation between the surface morphology and optical properties of AlGaN films in a microscopic scale. It is found that the suitable thickness of the LT AlN buffer for high quality AlGaN growth is around 20 nm. The Al compositional inhomogeneity of the AlGaN epilayer is attributed to the low lateral mobility of Al adatoms on the growing surface.

The effects of LT AlN buffer thickness on the properties of high Al composition AlGaN epilayers

To fabricate nitride-based ultraviolet optoelectronic devices, a deposition process for high-Al-composition AlGaN (Al content > 50%) films with reduced dislocation densities must be developed. This paper describes the growth of high-Al-composition AlGaN film on (0001) sapphire via a LT AIN nucleation layer by low pressure metalorganic chemical vapor deposition (LPMOCVD). The influence of the low temperature AIN buffer layer thickness on the high-Al-content AlGaN epilayer is investigated by triple-axis X-ray diffraction (TAXRD), scanning electron microscopy (SEM), and optical transmittance. The results show that the buffer thickness is a key parameter that affects the quality of the AlGaN epilayer. An appropriate thickness results in the best structural properties and surface morphology. (c) 2006 Elsevier B.V. All rights reserved.