A Single-Fundamental-Mode Photonic Crystal Vertical Cavity Surface Emitting Laser

Single-fundamental-mode photonic crystal (PhC) vertical cavity surface emitting lasers (VCSEL) are produced and their single-fundamental-mode performances are investigated and demonstrated. A two-dimensional PhC with single-point-defect structure is fabricated using UV photolithography and inductive coupled plasma reactive ion etching on the surface of the VCSEL's top distributed Bragg-reflector. The PhC VCSEL maintains single-fundamental-mode operating with output power 1.7 mW and threshold current 2.5 mA. The full width half maximum of the lasing spectrum is less than 0.1 nm, the far field divergence angle is less than 10 degrees and the side mode suppression ratio is over 35 dB. The device characteristics are analyzed based on the effective index model of the photonic crystal fiber. The experimental results agree well with the theoretical expectation.

Enhanced infrared emission from colloidal HgTe nanocrystal quantum dots on silicon-on-insulator photonic crystals

A two dimensional silicon-on-insulator based photonic crystal structure is used to enhance the emission from colloidal HgTe nanocrystal quantum dots embedded in a thin polymer film. The enhancement is resonant to the leaky eigenmodes of the photonic crystals due to coherent scattering effects. Transmittance and photoluminescence experiments are presented to map the leaky mode dispersion and the angle dependence of the emission enhancement factor, which reaches values up to 80 (650) for vertical (oblique) emission in the telecommunication wavelength range.

Surface characteristics of SiO2-TiO2 strip fabricated by laser direct writing

SiO2-TiO2 sol-gel films are deposited on SiO2/Si by dip-coating technique. The SiO2-TiO2 strips are fabricated by laser direct writing using all ytterbium fiber laser and followed by chemical etching. Surface structures, morphologies and roughness of the films and strips are characterized. The experimental results demonstrate that the SiO2-TiO2 sol-gel film is loose in Structure and a shrinkage concave groove forms if the film is irradiated by laser beam. The surface roughness of both non-irradiated and laser irradiated areas increases with the chemical etching time. But the roughness of laser irradiated area increases more than that of non-irradiated area under the same etching time. After being etched for 28 s, the surface roughness value of the laser irradiated area increases from 0.3 nm to 3.1 nm.

Experimental Demonstration on Structure-Parameter Dependence of Photonic Crystal Optical Spectrum

We present fabrication and experimental measurement of a series of photonic crystal waveguides and coupled structure of PC waveguide and PC micro-cavity. The complete devices consist of an injector taper down from 3 mu m into a triangular-lattice air-holes single-line-defect waveguide. We fabricated these devices on a silicon-on-insulator substrate and characterized them using tunable laser source. We've obtained high-efficiency light propagation and broad flat spectrum response of photonic-crystal waveguides. A sharp attenuation at photonic crystal waveguide mode edge was observed for most structures. The edge of guided band is shifted about 31 nm with the 10 nm increase of lattice constant. Mode resonance was observed in coupled structure. Our experimental results indicate that the optical spectra of photonic crystal are very sensitive to structure parameters.

Light extraction of GaN LEDs with 2-D photonic crystal structure

Ultraviolet photo-lithography is employed to introduce two-dimensional (2D) photonic crystal (PC) structure on the top surface of GaN-based light emitting diode (LED). PC patterns are transferred to 460-nm-thick transparent indium tin oxide (ITO) electrode by inductively coupled plasma (ICP) etching. Light intensity of PC-LED can be enhanced by 38% comparing with the one without PC structure. Rigorous coupled wave analysis method is performed to calculate the light transmission spectrum of PC slab. Simulation results indicate that total internal reflect angle which modulated by PC structure has been increased by 7 degrees, which means that the light extraction efficiency is enhanced outstandingly.

New type of multimode-interference-type thermo-optic variable optical attenuator

A thermo-optic variable optical attenuator (VOA) based on a Mach-Zehnder interferometer and multimode-interference coupler is fabricated. Not a single-mode but a multimode waveguide is used as the input and output structures of the optical field, which greatly reduces the coupling loss of the VOA with a normal single-mode fiber. The insertion loss of the fabricated VOA is 2.52 to 2.82 dB at the wavelength of 1520 to 1570 nm. The polarization dependent loss is 0.28 to 0.45 dB at the same wavelength range. Its maximum attenuation range is up to 26.3 dB when its power consumption is 369 mW. The response frequency of the fabricated VOA is about 10 kHz. (C) 2004 Society of Photo-Optical Instrumentation Engineers.

Thermal annealing effect on InAs/InGaAs quantum dots grown by atomic layer molecular beam epitaxy

The effect of rapid thermal annealing on the InAs quantum dots (QDs) grown by atomic layer molecular beam epitaxy and capped with InGaAs layer has been investigated using transmission electron microscopy and photoluminescence (PL). Different from the previously reported results, no obvious blueshift of the PL emission of QDs is observed until the annealing temperature increases up to 800 degreesC. The size and shape of the QDs annealed at 750 degreesC have hardly changed indicating the relatively weak Ga/In interdiffusion, which is characterized by little blueshift of the PL peak of QDs. The QD size increases largely and a few large clusters can be observed after 800 degreesC RTA, implying the fast interdiffusion and the formation of InGaAs QDs. These results indicate that the delay of the blueshift of the PL peak of QDs is correlated with the abnormal interdiffusion process, which can be explained by two possible reasons: the reduction of excess-As-induced defects and the redistribution of In, Ga atoms around the InAs QDs resulted from the sub-monolayer deposition of InGaAs capping layer. (C) 2004 Elsevier B.V. All rights reserved.

Preferred growth of nanocrystalline silicon in boron-doped nc-Si : H Films

Preferred growth of nanocrystalline silicon (nc-Si) was first found in boron-doped hydrogenated nanocrystalline (nc-Si:H) films prepared using plasma-enhanced chemical vapor deposition system. The films were characterized by high-resolution transmission electron microscope, X-ray diffraction (XRD) spectrum and Raman Scattering spectrum. The results showed that the diffraction peaks in XRD spectrum were at 2theta approximate to 47degrees and the exponent of crystalline plane of nc-Si in the film was (220). A considerable reason was electric field derived from dc bias made the bonds of Si-Si array according to a certain orient. The size and crystalline volume fraction of nc-Si in boron-doped films were intensively depended on the deposited parameters: diborane (B2H6) doping ratio in silane (SiH4), silane dilution ratio in hydrogen (H-2), rf power density, substrate's temperature and reactive pressure, respectively. But preferred growth of nc-Si in the boron-doped nc-Si:H films cannot be obtained by changing these parameters. (C) 2004 Elsevier Ltd. All rights reserved.

Structural phase transformations of ZnS nanocrystalline under high pressure

In-situ energy dispersive x-ray diffraction on ZnS nanocrystalline was carried out under high pressure by using a diamond anvil cell. Phase transition of wurtzite of 10 nm ZnS to rocksalt occurred at 16.0 GPa, which was higher than that of the bulk materials. The structures of ZnS nanocrystalline at different pressures were built by using materials studio and the bulk modulus, and the pressure derivative of ZnS nanocrystalline were derived by fitting the equation of Birch-Murnaghan. The resulting modulus was higher than that of the corresponding bulk material, which indicates that the nanomaterial has higher hardness than its bulk materials.

Cleaved-edge overgrowth of aligned InAs islands on GaAs(110)

A novel approach for positioning InAs islands on GaAs(110) by cleaved-edge overgrowth is reported. The first growth sample contains a strained InxGa1-xAs/GaAs superlattice of varying indium fraction and thickness, which acts as a strain nanopattern for the cleaved edge overgrowth. The formation of aligned islands is observed by means of atomic force microscopy. The ordering of the aligned islands and the structure of a single InAs island are found to depend on the properties of the underlying InxGa1-xAs/GaAs superlattice and molecular beam epitaxy growth conditions.

A novel method for positioning of InAs islands on GaAs(110)

A novel method for positioning of InAs islands on GaAs (110) by cleaved edge overgrowth is reported. The first growth sample contains strained InxGa1-xAs/GaAs superlattice (SL) of varying indium fraction, which acts as a strain nanopattern for the cleaved-edge overgrowth. Atoms incident on the cleaved edge will preferentially migrate to InGaAs regions where favorable bonding sites are available. By this method InAs island chains with lateral periodicity defined by the thickness of InGaAs and GaAs of SL have been realized by molecular beam epitaxy (MBE). They are observed by means of atomic force microscopy (AFM). The strain nanopattern's effect is studied by the different indium fraction of SL and MBE growth conditions. (c) 2005 Elsevier B.V. All rights reserved.

Quantum-dot growth simulation on periodic stress of substrate

InAs quantum dots (QDs) are grown on the cleaved edge of an InxGa1-xAs/GaAs supperlattice experimentally and a good linear alignment of these QDs on the surface of an InxGa1-xAs layer has been realized. The modulation effects of periodic strain on the substrate are investigated theoretically using a kinetic Monte Carlo method. Our results show that a good alignment of QDs can be achieved when the strain energy reaches 2% of the atomic binding energy. The simulation results are in excellent qualitative agreement with our experiments. (C) 2005 American Institute of Physics.

Site controlling of InAs quantum wires on cleaved edges of AlGaAs/GaAs superlattices

Site-controlled InAs quantum wires were fabricated on cleaved edges of AlGaAs/GaAs superlattices (SLs) by solid source molecular beam epitaxy. The cleaved edge of AlGaAs/GaAs SLs acted as a nanopattern for selective overgrowth after selective etching. By just growing 2.0 ML InAs without high temperature degassing, site-controlled InAs quantum wires were fabricated on the cleaved edge. Furthermore, atomic force microscopy demonstrates the diffusion of In atoms is strong toward the [00 (1) over bar] direction on the (110) surface.

Low power-consumption and high response frequency thermo-optic variable optical Attenuators based on silicon-on-insulator materials

A novel silicon-on-insulator thermo-optic variable optical attenuator with isolated grooves based on a multimode interference coupler principle is fabricated by the inductive coupled plasma etching technology. The maximum fibre-to-fibre insertion loss is lower than 2.2 dB, the dynamic attenuation range is from 0 to 30 dB in the wavelength range 1500-1600 nm, and the maximum power consumption is only 140 mW. The response frequency of the fabricated variable optical attenuator is about 30 kHz. Compared to the variable optical attenuator without isolated grooves, the maximum power consumption decreases more than 220 mW, and the response frequency rises are more than 20 kHz.

The structural and photoluminescence character of InAs quantum dots grown on a combined InAlAs and GaAs strained buffer

The structural and photoluminescence (PL) properties of the InAs quantum dots (QDs) grown on a combined InAlAs and GaAs strained buffer layer have been investigated by AFM and PL measurements. The dependence of the critical thickness for the transition from 2D to 3D on the thickness of GaAs layer is demonstrated directly by RHEED. The effects of the introduced-InAlAs layer on the density and the aspect ratio of QDs have been discussed.