Distribution of dislocations in GaSb and InSb epilayers grown on GaAs (001) vicinal substrates

GaSb and InSb epilayers grown on GaAs (001) vicinal substrates misoriented toward (111) plane were studied using high resolution x-ray diffraction. The results show that GaSb and InSb epilayers take on positive crystallographic tilt, and the asymmetric distribution of 60 degrees misfit dislocations in {111} glide planes have an effect on the tilt. In addition, the vicinal substrate influences the distribution of the threading dislocations in {111} glide planes, and the density of dislocation in the (111) plane is higher than in the ((1) over bar(1) over bar1) plane. A model was proposed to interpret the distribution of full width at half maximum, which can help us understand the formation and glide process of the dislocations. (C) 2009 American Institute of Physics. [DOI 10.1063/1.3115450]

GaAs-Based Metamorphic Long-Wavelength InAs Quantum Dots Grown by Molecular Beam Epitaxy

A bilayer stacked InAs/GaAs quantum dot structure grown by molecular beam epitaxy on an In0.05Ga0.95As metamorphic buffer is investigated. By introducing a InGaAs Sb cover layer on the upper InAs quantum dots (QDs) layers, the emission wavelength of the QDs is extended successfully to 1.533 mu m at room temperature, and the density of the QDs is in the range of 4 x 10(9) -8 x 10(9) cm(-2). Strong photoluminescence (PL) intensity with a full width at half maximum of 28.6 meV of the PL spectrum shows good optical quality of the bilayer QDs. The growth of bilayer QDs on metamorphic buffers offers a useful way to extend the wavelengths of GaAs-based materials for potential applications in optoelectronic and quantum functional devices.

Thickness dependent dislocation, electrical and optical properties in InN films grown by MOCVD

InN thin films with different thicknesses are grown by metal organic chemical vapor deposition, and the dislocations, electrical and optical properties are investigated. Based on the model of mosaic crystal, by means of X-ray diffraction skew geometry scan, the edge dislocation densities of 4.2 x 10(10) cm(-2) and 6.3 x 10(10) cm(-2) are fitted, and the decrease of twist angle and dislocation density in thicker films are observed. The carrier concentrations of 9 x 10(18) cm(-3) and 1.2 x 10(18) cm(-3) are obtained by room temperature Hall effect measurement. V-N is shown to be the origin of background carriers, and the dependence of concentration and mobility on film thickness is explained. By the analysis of S-shape temperature dependence of photoluminescence peak, the defects induced carrier localization is suggested be involved in the photoluminescence. Taking both the localization and energy band shrinkage effect into account, the localization energies of 5.05 meV and 5.58 meV for samples of different thicknesses are calculated, and the decrease of the carrier localization effect in the thicker sample can be attributed to the reduction of defects.

Room temperature photoluminescence of tensile-strained Ge/Si0.13Ge0.87 quantum wells grown on silicon-based germanium virtual substrate

We report a room temperature study of the direct band gap photoluminescence of tensile-strained Ge/Si0.13Ge0.87 multiple quantum wells grown on Si-based germanium virtual substrates by ultrahigh vacuum chemical vapor deposition. Blueshifts of the luminescence peak energy from the Ge quantum wells in comparison with the Ge virtual substrate are in good agreement with the theoretical prediction when we attribute the luminescence from the quantum well to the c Gamma 1-HH1 direct band transition. The reduction in direct band gap in the tensile strained Ge epilayer and the quantum confinement effect in the Ge/Si0.13Ge0.87 quantum wells are directly demonstrated by room temperature photoluminescence.

Annealing study of carrier concentration in gradient-doped GaAs/GaAlAs epilayers grown by molecular beam epitaxy

We measured the carrier concentration distribution of gradient-doped GaAs/GqAlAs epilayers grown by molecular beam epitaxy before and after annealing at 600 degrees C, using electrochemical capacitance voltage profiling, to investigate the internal variation of transmission-mode GaAs photocathodes arising from the annealing process. The results show that the carrier concentration increased after annealing. As a result, the total band-bending energy in the gradient-doped GaAs emission layer increased by 25.24% after annealing, which improves the pbotoexcited electron movement toward the surface. On the other hand, the annealing process resulted in a worse carrier concentration discrepancy between the GaAs and the GaAlAs, which causes a lower back interface potential barrier, decreasing the amount of high-energy photoelectrons. (C) 2009 Optical Society of America

Interfaces in InAs/GaSb Superlattices Grown by Molecular Beam Epitaxy

Short period InAs(4 ML)/GaSb(8 ML) superlattices (SLs) with InSb- and mixed-like (or Ga(1-x)In(x)As(1-)ySb(y)-like) interfaces (IFs) are grown by molecular-beam epitaxy (MBE) on (001) GaSb substrates at optimized growth temperature. Raman scattering reveals that two kinds of IFs can be formed by controlling shutter sequences. X-ray diffraction (XRD) and atomic force microscopy (AFM) demonstrate that SLs with mixed-like IFs are more sensitive to growth temperature than that with InSb-like IFs. The photoluminescence (PL) spectra of SLs with mixed-like IFs show a stronger intensity and narrower line width than with InSb-like IFs. It is concluded that InAs/GaSb SLs with mixed-like IFs have better crystalline and optical properties.

Long-Wavelength Emission InAs Quantum Dots Grown on InGaAs Metamorphic Buffers

In this work, InAs quantum dots (QDs) grown on a linear graded InGaAs metamorphic buffer layer by molecular beam epitaxy have been investigated. The growth of the metamorphic buffer layers was carefully optimized, yielding a smooth surface with a minimum root mean square of roughness of less than 0.98 nm as measured by atomic force microscopy (AFM). InAs QDs were then grown on the buffer layers, and their emission wavelength at room-temperature is 1.49 mu m as measured by photoluminescence (PL). The effects of post-growth rapid thermal annealing (RTA) on the optical properties of the InAs QDs were investigated. After the RTA, the PL peak of the QDs was blue-shifted and the full width at half maximum decreased.

GaAs Based InAs/GaSb Superlattice Short Wavelength Infrared Detectors Grown by Molecular Beam Epitaxy

InAs/GaSb superlattice (SL) short wavelength infrared photoconduction detectors are grown by molecular beam epitaxy on GaAs(001) semi-insulating substrates. An interfacial misfit mode AlSb quantum dot layer and a thick GaSb layer are grown as buffer layers. The detectors containing a 200-period 2ML/8ML InAs/GaSb SL active layer are fabricated with a pixel area of 800 x 800 mu m(2) without using passivation or antireflection coatings. Corresponding to the 50% cutoff wavelengths of 2.05 mu m at 77K and 2.25 mu m at 300 K, the peak detectivities of the detectors are 4 x 10(9) cm.Hz(1/2)/W at 77K and 2 x 10(8) cm.Hz(1/2)/W at 300 K, respectively.

Metamorphic InGaAs Quantum Well Laser Diodes at 1.5 mu on GaAs Grown by Molecular Beam Epitaxy

We report a 1.5-mu m InGaAs/GaAs quantum well laser diode grown by molecular beam epitaxy on InGaAs metamorphic buffers. At 150 K, for a 1500 x 10 mu m(2) ridge waveguide laser, the lasing wavelength is centred at 1.508 mu m and the threshold current density is 667 A/cm(2) under pulsed operation. The pulsed lasers can operate up to 286 K.

Dependence of current-voltage characteristics of pseudomorphic AlAs/In0.53Ga0.47As/InAs resonant tunnelling diodes on quantum well widths

This paper studies the dependence of I - V characteristics on quantum well widths in AlAs/In0.53Ga0.47As and AlAs/In0.53Ga0.47As/InAs resonant tunnelling structures grown on InP substrates. It shows that the peak and the valley current density in the negative differential resistance region are closely related with quantum well width. The measured peak current density, valley current densities and peak-to-valley current ratio of resonant tunnelling diodes are continually decreasing with increasing well width.

Al composition variations in AlGaN films grown on low-temperature GaN buffer layer by metalorganic chemical vapor deposition

We have investigated the optical properties of AlGaN grown on sapphire. It is found that two main luminescence peaks occur in the cathodoluminescence (CL) spectra of AlGaN films, and their energy separation increases with the increase of Al source flux during the growth. Spatially resolved CL investigations have shown that the line splitting is a result of variation of AlN mole fraction within the layer. The Al composition varies in both lateral and vertical direction. It is suggested that the difference in the surface mobility of Al and Ga atoms, especially, its strong influence on the initial island coalescence process and the formation of island-like regions on the uneven film surface, is responsible for the Al composition inhomogeneity. (C) 2008 Elsevier B.V. All rights reserved.

Effect of beta-irradiation on photoluminescence of MOCVD grown GaN

The effect of beta particles interaction on the optical properties of MOCVD grown GaN is reported. A significant change in luminescence properties of GaN is observed after exposing the material with 0.6 MeV beta particles with low dose of 10(12) cm(-2). The results obtained from photoluminescence measurements of irradiated GaN samples in low dose are found contradictory to those reported in literature for samples irradiated with heavy dose (> 10(15) cm(-2)) of electron. An increase in intensity of yellow luminescence has been observed with increasing dose of beta particles which is in disagreement to the already reported results in literature for heavily irradiated samples. A model has been proposed to sort out this inconsistency. The increase in YL intensity at low dose is attributed to the increase in concentration of VGaON complex whereas production of non-radiative VGaON clusters is assumed to justify the decrease in YL intensity at high dose.

Strain status in ZnO film on sapphire substrate with a GaN buffer layer grown by metal-source vapor phase epitaxy

ZnO film of 8 mu m thickness was grown on a sapphire (0 0 1) substrate with a GaN buffer layer by a novel growth technique called metal-source vapor phase epitaxy (MVPE). The surface of ZnO film measured by scanning electron microscope (SEM) is smooth and shows many regular hexagonal features. The full width at half maximum (FWHM) of ZnO(0 0 2) and (1 0 2) omega-scan rocking curves are 119 and 202 arcsec, corresponding a high crystal quality. The status of the strain in ZnO thick film was particularly analyzed by X-ray diffraction (XRD) omega-20 scanning. The results show that the strain in ZnO film is compressive, which is also supported by Raman scattering spectroscopy. The compressive strain can solve the cracking problem in the quick growth of ZnO thick film. (c) 2008 Elsevier Ltd. All rights reserved.

Hillocks and hexagonal pits in a thick film grown by HVPE

A GaN film with a thickness of 250 mu m was grown on a GaN/sapphire template in a vertical hydride vapor phase epitaxy (HVPE) reactor. The full-width at half-maximum (FWHM) values of the film were 141 and 498 arcsec for the (0 0 2) and (1 0 2) reflections, respectively. A sharp band-edge emission with a FWHM of 20 meV at 50 K was observed, which corresponded to good crystalline quality of the film. Some almost circular-shaped hillocks located in the spiral growth center were found on the film surface with dimensions of 100 mu m, whose origin was related to screw dislocations and micropipes. Meanwhile, large hexagonal pits also appeared on the film surface, which had six triangular {1 0 (1) over bar 1} facets. The strong emission in the pits was dominated by an impurity-related emission at 377 nm, which could have been a high-concentration oxygen impurity. (c) 2008 Elsevier Ltd. All rights reserved.

InP Based PD/EAM Integrated Photonic Switch

A new compact three-port InP based PD/EAM (photo-detector/electro-absorption modulator) integrated photonic switch is reported. The device demonstrates bi-directional wavelength conversion over 20 nm at 2.5 Gbit/s with a low input optical power of about 20 mW.