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.

Comparison of short period InAs/GaSb superlattices on GaSb and GaAs substrates

Type II superlattices (SLs) short period InAs(4ML)/GaSb(8ML) were grown by molecular-beam epitaxy on lattice-mismatched GaAs substrates and on GaSb substrates. A smooth GaSb epilayer was formed on GaAs substrates by inserting mulit-buffer layers including an interfacial misfit mode AlSb quantum dot layer and AlSb/GaSb superlattices smooth layer. SLs grown on GaAs substrates (GaAs-based SLs) showed well-resolved satellite peaks in XRD. GaSb-based SLs with better structural quality and smoother surface showed strong photoluminescence at 2.55 mu m with a full width at half maximum (FWHM) of 20 meV, narrower than 31 meV of GaAs-based SLs. Inferior optical absorption of GaAs-based SL was observed in the range of 2-3 mu m. Photoresponse of GaSb-based SLs showed the cut-off wavelength at 2.6 mu m.

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.

Determination of the tilt and twist angles of curved GaN layers by high-resolution x-ray diffraction

The full-width at half-maximum (FWHM) of an x-ray rocking curve (XRC) has been used as a parameter to determine the tilt and twist angles of GaN layers. Nevertheless, when the thickness of GaN epilayer reaches several microns, the peak broadening due to curvature becomes non-negligible. In this paper, using the (0 0 l), l = 2, 4, 6, XRC to minimize the effects of wafer curvature was studied systematically. Also the method to determine the tilt angle of a curved GaN layer was proposed while the Williamson-Hall plot was unsuitable. It was found that the (0 0 6) XRC-FWHM had a significant advantage for high-quality GaN layers with the radius curvature of r less than 3.5 m. Furthermore, an extrapolating method of gaining a reliable tilt angle has also been proposed, with which the calculated error can be improved by 10% for r < 2 m crystals compared with the (0 0 6) XRC-FWHM. In skew geometry, we have demonstrated that the twist angles deriving from the (2 0 4) XRC-FWHM are in accord with those from the grazing incidence in-plane diffraction (IP-GID) method for significantly curved samples.

All-optical continuously tunable delay with a high linear-chirp-rate fiber Bragg grating based on four-wave mixing in a highly-nonlinear photonic crystal fiber

A scheme for hi-fi all-optical continuously tunable delay is proposed. The signal wavelength is converted to a desired idler wavelength and converted back after being delayed by a high linear-chirp-rate (HLCR) fiber Bragg grating (FBG) based on four-wave mixing (FWM) in a highly-nonlinear photonic crystal fiber (HN-PCF). In our experiment, 400 ps (more than 8 full width of half maximum, FWHM) tunable delay is achieved for a 10 GHz clock pulse with relative pulse width broaden ratio (RPWBR) of 2.08%. The power penalty is only 0.3 dB at 10(-9) BER for a 10 Gb/s 2(31)-1 pseudo random bit sequence (PRBS) data. (c) 2009 Elsevier B.V. All rights reserved.

Holographic fabricated photonic-crystal distributed-feedback quantum cascade laser with near-diffraction-limited beam quality

We demonstrate the fabrication and characterization of photonic-crystal distributed-feedback quantum cascade laser emitting at 4.7 mu m. The tilted rectangular-lattice PCDFB structure was defined using a multi-exposure of two-beam holographic lithography. The devices exhibit the near-diffraction-limited beam emission with the full width at half maximum of the far-field divergence angles about 4.5 degrees and 2.5 degrees for stripe widths of 55 mu m and 95 mu m, respectively. Single-mode emission with a side mode suppression ratio of approximate to 20 dB is achieved in the temperature range (80-210 K). The single-facet output power is above 1 W for a 95 mu m x 2.5 mm laser bar at 85 K in pulsed operation. (C) 2009 Optical Society of America

1.55 mu m Ge islands resonant-cavity-enhanced detector with high-reflectivity bottom mirror

A 1.55 mum Ge islands resonant-cavity-enhanced (RCE) detector with high-reflectivity bottom mirror was fabricated by a simple method. The bottom mirror was deposited in the hole formed by anisotropically etching in a basic solution from the back side of the sample with the buried SiO2 layer in silicon-on-insulator substrate as the etch-stop layer. Reflectivity spectrum indicates that the mirror deposited in the hole has a reflectivity as high as 99% in the range of 1.2-1.65 mum. The peak responsivity of the RCE detector at 1543.8 nm is 0.028 mA/W and a full width at half maximum of 5 nm is obtained. Compared with the conventional p-i-n photodetector, the responsivity of RCE detector has a nearly threefold enhancement. (C) 2004 American Institute of Physics.

Effect of the ratio of TMIn flow to group III flow on the properties of InGaN/GaN multiple quantum wells

Triple-axis x-ray diffraction (TXRD) and photoluminescence (PL) spectra are used to assess the influence of the ratio of TMIn flow to group III flow on structural defects, such as dislocations and interface roughness, and optical properties of multiple quantum wells(MQWs). In this paper the mean densities of edge and screw dislocations in InGaN/GaN MQWs are obtained by W scan of every satellite peak of (0002) symmetric and (1012) asymmetric diffractions. At the same time, the interface roughness is measured by the radio of the full width at half maximum of satellite peaks to the peak orders. The experimental results showed that the density of dislocation, especially of edge dislocation, and interface roughness increase with the increase of the ratio, which leads to the decrease of PL properties. It also can be concluded that the edge dislocation acts as nonradiative recombination centers in InGaN/GaN MQWs. Also noticed is that the variation of the ratio has more influence on edge dislocation than on screw dislocation.

Fabrication of 1.55-mu m Si-based resonant cavity enhanced photodetectors using sol-gel bonding

In this work, a novel bonding method using silicate gel as the bonding medium was developed to fabricate an InGaAs narrow-band response resonant cavity enhanced photodetector on a silicon substrate. The bonding was performed at a low temperature of 350 degreesC without any special treatment on bonding surfaces and a Si-based narrow-band response InGaAs photodetector was successfully fabricated, with a quantum efficiency of 34.4% at the resonance wavelength of 1.54 mum, and a full-width at half-maximum of about 27 nm. The photodetector has a linear photoresponse up to 4-mW optical power under 1.5 V or higher reverse bias. The low temperature wafer bonding process demonstrates a great potential in device fabrication.

Luminescence properties of self-assembled InAs/GaAs quantum dots covered by InAlAs and InGaAs combination strain-reducing layer

We report the photoluminescence (PL) and structural properties of self-assembled InAs/GaAs quantum dots (QDs) covered by In0.2Al0.8As and In0.2Ga0.8As combination strain-reducing layer (SRL). By introducing a thin InAlAs layer, the ground state emission wavelength redshifts, and the energy splitting between the ground and first-excited states increases to 85 meV at 10 K. The energy splitting further increases to 92 meV and the temperature dependence of full width at half maximum (FWHM) changes for QDs with different SRL after the multi-stacking. These results are attributed to the fact that the combination layer has different effects on QDs compared to the InGaAs SRL.

High-indium-content InxGa1-xAs/GaAs quantum wells with emission wavelengths above 1.25 mu m at room temperature

High-indium-content InxGa1-xAs/GaAs single/multi-quantum well (SQW/MQW) structures have been systematically investigated. By optimizing the molecular-beam epitaxy growth conditions, the critical thickness of the strained In0.475Ga0.525As/GaAs QWs is raised to 7 nm, which is much higher than the value given by the Matthews and Blakeslee model. The good crystalline quality of the strained InGaAs/GaAs MQWs is proved by x-ray rocking curves. Photoluminescence measurements show that an emission wavelength of 1.25 mum at room temperatures with narrower full width at half maximum less than 30 meV can be obtained. The strain relaxation mechanism is discussed using the Matthews-Blakeslee model. (C) 2004 American Institute of Physics.

A novel extremely broadband superluminescent diode based on symmetric graded tensile-strained bulk InGaAs

A novel broadband superluminescent diode (SLD), which has a symmetric graded tensile-strained bulk InGaAs active region, is developed. The symmetric-graded tensile-strained bulk InGaAs is achieved by changing the group III TMGa source flow only during its growth process by low-pressure metalorganic vapor-phase epitaxy (LP-MOVPE), in which the much different tensile strain is introduced simultaneously. At 200mA injection current, the full width at half maximum (FWHM) of the emission spectrum of the SLID can be up to 122nm, covering the range of 1508-1630nm, and the output power is 11.5mW.

Fabrication of GdSi2 film by low-energy ion-beam implantation

Single-phase gadolinium disilicide was fabricated by a low-energy ion-beam implantation technique. Auger electron spectroscopy and X-ray photoelectron spectroscopy were used to determine the composition and chemical states of the film. The structure of the sample was analyzed by X-ray diffraction and the surface morphology was investigated by scan electron microscopy. Based on the measurements, only orthorhombic GdSi2 phase was found in the sample and the surface morphology was pitting. After annealing at 350degreesC for 30 min at Ar atmosphere, the full-width at half-maximum of GdSi2 became narrower. It indicates that the GdSi2 is crystallized better after annealing. (C) 2003 Elsevier B.V. All rights reserved.

Anomalous temperature dependence of photoluminescence from stoichiometric GD(2)O(3-x) film

A stoichiometric Gd2O3-x thin film has been grown on a silicon (10 0) substrate with a low-energy dual ion-beam epitaxial technique. Gd2O3-x shares Gd2O3 structures although there are many oxygen deficiencies in the film. The photoluminescence (PL) measurements have been performed in a temperature range 5-300 K. The detailed characters of the peak position, the full-width at half-maximum (FWHM) and the peak intensity at different temperature were reported. An anomalous intensity behavior of the PL spectra has been observed, which is similar to that of some other materials such as porous silicon and silicon nanocrystals in silicon dioxide. Therefore, we suggest that the nanoclusters with the oxygen deficiencies contribute to the PL emission and employ the model of singlet-triplet exchange splitting of exciton to discuss the four peaks observed in the experiment. (C) 2003 Elsevier B.V. All rights reserved.