Investigations on oxide-free InGaAlAs waveguides grown by narrow stripe selective MOVPE

Oxide-free InGaAlAs waveguides have been grown on the InP substrates patterned with pairs of SiO2 mask stripes using narrow stripe selective MOVPE. The mask stripe width is varied from 0 to 40 pm, while the window region width between a pair of mask stripes is fixed at 1.5, 2.5 and 3.5 mu m, respectively. Smooth surface s and flat interfaces are obtained in the selectively grown InQaAlAs waveguides. There exhibit strong dependences of the thickness enhancement ratio and the photoluminescence (PL) spectrum on the mask stripe width and the window region width for the InGaAlAs wavegwdes. A large PL peak wavelength shift of 79 nm and a PL full width of at half maximum (FWHM) of less than 64 meV are obtained simultaneously. Some possible interpretations for our investigations are presented by considering both the migration effect from a masked region (MMR) and the lateral vapor diffusion effect (LVD).

Growth mechanism of InGaAlAs waveguides by narrow stripe selective MOVPE

Growth mechanism of InGaAlAs waveguides by narrow stripe selective MOVPE has been studied. Both the InGaAlAs bulk waveguides and the InGaAlAs MQW waveguides were successful grown on the patterned substrates at optimized growth conditions. The mask stripe width varied from 0 to 40 mu m, while the window region width between a pair of mask stripes was fixed 2.5 mu m. These selectively grown waveguides were covered by specific InP layers, which can keep the InGaAlAs waveguides from being oxidized during the fabrication of devices. In particular, there exhibit strong dependences of the photoluminescence (PL) spectrum on the mask stripe width for the samples. The results were explained in considering both the migration effect from a masked region (MMR) and the lateral vapor diffusion effect (LVD).

Optical and structural properties of ZnO films grown on Si(100) substrates by MOCVD - art. no. 60290G

High quality ZnO films have been successfully grown on Si(100) substrates by Metal-organic chemical vapor deposition (MOCVD) technique. The optimization of growth conditions (II-VI ratio, growth temperature, etc) and the effects of film thickness and thermal treatment on ZnO films' crystal quality, surface morphology and optical properties were investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), and photoluminescence (PL) spectrum, respectively. The XRD patterns of the films grown at the optimized temperature (300 degrees C) show only a sharp peak at about 34.4 degrees corresponding to the (0002) peak of hexagonal ZnO, and the FWHM was lower than 0.4 degrees. We find that under the optimized growth conditions, the increase of the ZnO films' thickness cannot improve their structural and optical properties. We suggest that if the film's thickness exceeds an optimum value, the crystal quality will be degraded due to the large differences of lattice constant and thermal expansion coefficient between Si and ZnO. In PL analysis, samples all displayed only ultraviolet emission peaks and no observable deep-level emission, which indicated high-quality ZnO films obtained. Thermal treatments were performed in oxygen and nitrogen atmosphere, respectively. Through the analysis of PL spectra, we found that ZnO films annealing in oxygen have the strongest intensity and the low FWHM of 10.44 nm(106 meV) which is smaller than other reported values on ZnO films grown by MOCVD.

Growth and characterization of 4H-SiC by horizontal hot-wall CVD

4H-SiC layers have been homoepitaxially grown at 1500 degrees C with the use of a horizontal hot-wall chemical vapor deposition (CVD) system, which was built in the author's group. The typical growth rate was 2 mu m/h at a pressure of 40 Torr. The background donor concentration has been reduced to 2.3 x 10(15) cm(-3) during a prolonged growth run. It confirmed the idea that the high background concentration of thin films was caused by the impurities inside the susceptor and thermal insulator The FWHM of x-ray co-rocking curves show 9 similar to 15 aresecs in five different areas of a 32-mu m-thick 4H-SiC epilayer The free exciton peaks dominated in the near-band-edge low-temperature photoluminescence spectrum (LTPL), indicating high crystal quality.

Raman scattering study on diluted magnetic semiconductor Ga1-xMnxAs prepared by Mn-ion implantation

Raman scattering measurements have been performed in diluted magnetic semiconductor Ga1-xMnxAs prepared by Mn-ion implantation, deposition, and post-annealing technique. It is found that the Raman spectrum measured from the implanted surface of the sample shows some new weak modes in addition to the GaAs-like modes which are observed from the unimplanted surface. The new vibrational modes observed are assigned to MnAs-like modes. The coupled LO-phonon plasmon mode, and Mn and As related vibrational modes caused by Mn-ion implantation, deposition, and post-annealing are also observed. Furthermore, the GaAs-like modes are found to be shifted by approximately 4 cm(-1) in the lower frequency side, compared with those observed from the unimplanted surface.

A silicon light emitting devices in standard CMOS technology

A silicon light emitting device is designed and simulated. It is fabricated in 0.6 mum standard CMOS technology. The device can give more than 1 muW optical power of visible light under reverse breakdown. The device can be turned on at a bias of 0.88 V and work in a large range of voltage: 1.0-6.0 V The external electrical-optical conversion efficiency is more than 10(-6). The optical spectrum of the device is between 540-650 nm, which have a clear peak near 580 nm. The emission mechanism can be explained by a hot carrier direct recombination model.

1.55 mu m Ge islands resonant-cavity-enhanced narrowband detector

The high quality Ge islands material with 1.55 mu m photo-response grown on Sol substrate is reported. Due to the modulation of the cavity formed by the mirrors at the surface and the buried SiO2 interface, seven sharp and strong peaks with narrow linewidth are found. And a 1.55 mu m Ge islands resonant-cavity-enhanced (RCE) detector with narrowband was fabricated by a simple method. The bottom mirror was deposited in the hole formed by anisotropically etching, in a basic solution from the backside 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 mu m. 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.

Quantifying the effectiveness of SiO2/Au light trapping nanoshells for thin film poly-Si solar cells

In order to enhance light absorption of thin film poly-crystalline silicon (TF poly-Si) solar cells over a broad spectral range, and quantify the effectiveness of nanoshell light trapping structure over the full solar spectrum in theory, the effective photon trapping flux (EPTF) and effective photon trapping efficiency (EPTE) were firstly proposed by considering both the external quantum efficiency of TF poly-Si solar cell and scattering properties of light trapping structures. The EPTF, EPTE and scattering spectrum exhibit different behaviors depending on the geometric size and density of nanoshells that form the light trapping layer. With an optimum size and density of SiO2/Au nanoshell light trapping layer, the EPTE could reach up to 40% due to the enhancement of light trapping over a broad spectral range, especially from 500 to 800 nm.

Electrical and Optical Phase Transition Properties of Nano Vanadium Dioxide Thin Films

Nano-vanadium dioxide thin films were prepared through thermal annealing vanadium oxide thin films deposited by dual ion beam sputtering. The nano-vanadium dioxide thin films changed its state from semiconductor phase to metal phase through heating by homemade system. Four point probe method and Fourier transform infrared spectrum technology were employed to measure and anaylze the electrical and optical semiconductor-to-metal phase transition properties of nano-vanadium dioxide thin films, respectively. The results show that there is an obvious discrepancy between the semiconductor-to-metal phase transition properties of electrical and optical phase transition. The nano-vanadium dioxide thin films' phase transiton temperature defined by electrical phase transiton property is 63 degrees C, higher than that defined by optical phase transiton property at 5 mu m, 60 degrees C; and the temperature width of electrical phase transition duration is also wider than that of optical phase transiton duration. The semiconductor-to-metal phase transiton temperature defined by optical properties increases with increasing wavelength in the region of infrared wave band, and the occuring temperature of phase transiton from semiconductor to metal also increases with wavelength increasing, but the duration temperature width of transition decreases with wavelength increasing. The phase transition properties of nano-vanadium dioxide thin film has obvious relationship with wavelength in infrared wave band. The phase transition properties can be tuned through wavelength in infrared wave band, and the semiconductor-to-metal phase transition properties of nano vanadiium dioxide thin films can be better characterized by electrical property.

12 W high efficiency single frequency ring laser

Single-frequency output power of 12 W at 1064 nm is demonstrated. Pumped by a fiber-coupled diode laser, the Nd:YVO4 produces 58.6% of the slope efficiency with respect to absorbed pump power, and 52.7% of the optical-optical efficiency and nearly diffraction-limited output with a beam quality parameter of M-2 approximate to 1.11. To the best of our knowledge, this is the highest slope efficiency and optical-optical efficiency in single-frequency Nd:YVO4 ring laser. The slope efficiency of the single frequency laser is close to the limit of the efficiency. [GRAPHICS] output spectrum of the single-frequency Nd:YVO4 ring laser

Photovoltaic effect of tin disulfide with nanocrystalline/amorphous blended phases

Tin disulfide (SnS2) nanocrystalline/amorphous blended phases were synthesized by mild chemical reaction. Both X-ray diffraction and transmission electron microscopy measurements demonstrate that the as-synthesized particles presented very small size, with a diameter of only a few nanometers. The photoluminescence (PL) spectrum suggests efficient splitting of photo-generated excitons in poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) and SnS2 hybrid films. Organic/inorganic hybrid solar cells comprising MDMO-PPV and SnS2 were prepared, giving photovoltage, photocurrent, fill factor and efficiency values of 0.702 V, 0.549 mA/cm(2), 0.385 and 0.148%, respectively, which suggests that this phase-blended inorganic semiconductor can also serve as a promising solar energy material. (C) 2009 Elsevier Ltd. All rights reserved.

A broadband external cavity tunable InAs/GaAs quantum dot laser by utilizing only the ground state emission

A broadband external cavity tunable laser is realized by using a broad-emitting spectral InAs/GaAs quantum dot (QD) gain device. A tuning range of 69 nm with a central wavelength of 1056 nm, is achieved at a bias of 1.25 kA/cm(2) only by utilizing the light emission from the ground state of QDs. This large tunable range only covers the QD ground-state emission and is related to the inhomogeneous size distribution of QDs. No excited state contributes to the tuning bandwidth. The application of the QD gain device to the external cavity tunable laser shows its immense potential in broadening the tuning bandwidth. By the external cavity feedback, the threshold current density can be reduced remarkably compared with the free-running QD gain device.

Strain-Compensated InGaAs/InAlAs Quantum Cascade Detector of 4.5 mu m Operating at Room Temperature

We present a strain-compensated InP-based InGaAs/InAlAs photovoltaic quantum cascade detector grown by solid source molecular beam epitaxy. The detector is based on a vertical intersubband transition and electron transfer on a cascade of quantum levels which is designed to provide longitudinal optical phonon extraction stairs. By careful structure design and growth, the whole epilayer has a residual strain toward InP substrate of only -2.8 x 10(-4). A clear narrow band detection spectrum centered at 4.5 mu m has been observed above room temperature for a device with 200 x 200 mu m(2) square mesa.

Broadband external cavity tunable quantum dot lasers with low injection current density

Broadband grating-coupled external cavity laser, based on InAs/GaAs quantum dots, is achieved. The device has a wavelength tuning range from 1141.6 nm to 1251.7 nm under a low continuous-wave injection current density (458 A/cm(2)). The tunable bandwidth covers consecutively the light emissions from both the ground state and the 1st excited state of quantum dots. The effects of cavity length and antireflection facet coating on device performance are studied. It is shown that antireflection facet coating expands the tuning bandwidth up to similar to 150 nm, accompanied by an evident increase in threshold current density, which is attributed to the reduced interaction between the light field and the quantum dots in the active region of the device.

Improved electroluminescence from n-ZnO/AlN/p-GaN heterojunction light-emitting diodes

n-ZnO/p-GaN heterojunction light-emitting diodes with and without a sandwiched AlN layer were fabricated. The electroluminescence (EL) spectrum acquired from the n-ZnO/p-GaN displays broad emission at 650 nm originating from ZnO and weak emission at 440 nm from GaN, whereas the n-ZnO/AlN/p-GaN exhibits strong violet emission at 405 nm from ZnO without GaN emission. The EL intensity is greatly enhanced by inserting a thin AlN intermediate layer and it can be attributed to the suppressed formation of the GaOx interfacial layer and confinement effect rendered by the AlN potential barrier layer.