Laser diode integrated with a dual-waveguide spot-size converter by low-energy ion implantation quantum well intermixing

A ridge laser diode monolithically integrated with a buried-ridge-structure dual-waveguide spot-size converter operating at 1.58 mu m is successfully fabricated by means of low-energy ion implantation quantum well intermixing and asymmetric twin waveguide technology. The passive waveguide is optically combined with a laterally tapered active core to control the mode size. The devices emit in a single transverse and quasi single longitudinal mode with a side mode suppression ratio of 40.0dB although no grating is fabricated in the LD region. The threshold current is 50 mA. The beam divergence angles in the horizontal and vertical directions are as small as 7.3 degrees x 18.0 degrees, respectively, resulting in 3.0dB coupling loss With a cleaved single-mode optical fibre.

1.55 mu m spot-size converter with monolithically integrated laser diode by conventional process

A novel 1.55 mum laser diode (LD) with monolithically integrated spot-size converter (SSC) is designed and fabricated using conventional photolithography and the chemical wet etching process. For the laser diode, a ridge double-core structure is employed. For the spot-size converter, a buried double-waveguide structure is incorporated. The laterally tapered active core is designed and optically combined with the thin passive core to control the size of the mode. The threshold current was measured to be 40 mA together with high slope efficiency of 0.35 W A(-1). The beam divergence angles in the horizontal and vertical directions were as small as 14.9degrees and 18.2degrees, respectively.

Ridge waveguide laser integrated with spot-size converter in a single step epitaxial for high coupling efficiency to single-mode fibres

A 1.55-mum laser diode integrated with a spot-size converter was fabricated in a single step epitaxial by using the conventional photolithography and chemical wet etching process. The device was constructed by a conventional ridge waveguide active layer and a larger passive ridge-waveguide layer. The threshold current was 40 mA together with high slope efficiency of 0.24 W/A. The beam divergence angles in the horizontal and vertical directions were as small as 12.0degrees x 15.0degrees, respectively, resulting in about 3.2-dB coupling losses with a cleaved optical fibre.

Electroabsorption-Modulated DFB laser Integrated.With dual-core spot-size converters

A 1.55-mu m single shallow ridge electroabsorptionmodulated distributed feedback laser that is monolithically integrated with a buried-ridge-stripe dual-core spot-size converter (SSC) at the input and output ports was fabricated by combining selective area growth, quantum-well intermixing, and dual-core integration techniques simultaneously. These devices exhibit a threshold current of 34 mA, a side mode suppression ratio of 38.0 dB, a 3-dB modulation bandwidth of 11.0 GHz, and a modulator extinction ratio of 25.0 dB dc. The output beam divergence angles of the SSC in the horizontal and vertical directions are as small as 7.3 degrees x 18 degrees, respectively, resulting in 3.2-dB coupling loss with a cleaved single-mode optical fiber.

Electroabsorption modulator integrated with buried-ridge-stripe dual-core spot-size converter by quantum-well intermixing

A single shallow ridge electroabsorption modulator monolithically integrated with a buried-ridge-stripe dual-core spot-size converter at the input and output port was fabricated by combining quantum-well intermixing and dual-core integration techniques simultaneously, using only a two-step low-pressure metal-organic vapor phase epitaxial process, conventional photolithography, and a chemical wet etching process. The optical insertion loss of the modulator in the on-state and the dc extinction ratio between 0 and -3 V at 1550 nm was -7.5 and 16 dB, respectively. The 3-dB modulation bandwidth was more than 10.0 GHz in electrical-optical response.

Influence of longitudinal electric field on the hot-phonon effect in quantum wells

Using the Huang-Zhu model [K. Huang and B.-F. Zhu, Phys. Rev. B 38, 13377 (1988)] for the optical phonons and associated carrier-phonon interactions in semiconductor superlattices, the effects of longitudinal electric field on the energy-loss rates (ELRs) of hot carriers as well as on the hot-phonon effect (HPE) in GaAs/AlAs quantum wells (QWs) are studied systematically. Contributions of various bulklike and interface phonons to the hot-carrier relaxation are compared in detail, and comprehensively analyzed in relation to the intrasubband and intersubband scatterings for quantum cascade lasers. Due to the broken parity of the electron (hole) states in the electric field, the bulklike modes with antisymmetric potentials are allowed in the intrasubband relaxation processes, as well as the modes with symmetric potentials. As the interface phonon scattering is strong only in narrow wells, in which the electric field affects the electron (hole) states little, the ELRs of hot carriers through the interface phonon scattering are not sensitive to the electric field. The HPE on the hot-carrier relaxation process in the medium and wide wells is reduced by the electric field. The influence of the electric field on the hot-phonon effect in quantum cascade lasers is negligible. When the HPE is ignored, the ELRs of hot electrons in wide QWs are decreased noticeably by the electric field, but slightly increased by the field when considering the HPE. In contrast with the electrons, the ELRs of hot holes in wide wells are increased by the field, irrespective of the HPE. (c) 2006 American Institute of Physics.

1.55-mu m Ridge DFB laser and electroabsorption modulator integrated with buried-ridge-stripe dual-waveguide spot-size converter output

A 1.55-mu m ridge distributed feedback laser and electroabsorption modulator monolithically integrated with a buried-ridge-stripe dual-waveguide spot-size converter (SSC) at the output port for low-loss coupling to a cleaved single-mode optical fiber was fabricated by means of selective area growth, quantum-well intermixing, and dual-core technologies. These devices exhibit threshold current of 28 mA, 3-dB modulation bandwidth of 12.0 GHz, modulator extinction ratios of 25.0-dB dc. The output beam divergence angles of the SSC in the horizontal and vertical directions are as small as 8.0 degrees x 12.6 degrees, respectively, resulting in 3.2-dB coupling loss with a cleaved single-mode optical fiber.

Electroabsorption modulated semiconductor optical amplifier monolithically integrated with spot-size converters

We have demonstrated an electroabsorption modulator (EAM) and semiconductor optical amplifier (SOA) monolithically integrated with novel dual-waveguide spot-size converters (SSCs) at the input and output ports for low-loss coupling to planar light-guide circuit silica waveguide or cleaved single-mode optical fiber. The device is fabricated by means of selective-area MOVPE growth (SAG), quantum well intermixing (QWI) and asymmetric twin waveguide (ATG) technologies with only three steps low-pressure MOVPE growth. For the device structure, in SOA/EAM section, double ridge structure was employed to reduce the EAM capacitances and enable high bit-rate operation. In the SSC sections, buried ridge stripe (BRS) were incorporated. Such a combination of ridge, ATG and BRS structure is reported for the first time in which it can take advantage of both easy processing of ridge structure and the excellent mode characteristic of BRS. At the wavelength range of 1550-1600 nm, lossless operation with extinction ratios of 25 dB DC and more than 10 GHz 3-dB bandwidth is successfully achieved. The beam divergence angles of the input and output ports of the device are as small as 8.0 degrees x 12.6 degrees, resulting in 3.0 dB coupling loss with cleaved single-mode optical fiber. (c) 2005 Elsevier B.V. All rights reserved.

Structual and optoelectronic properties of polycrystalline silicon thin films prepared by hot-wire chemical vapor deposition at low temperatures

Polycrystalline silicon thin films were prepared by hot-wire chemical vapor deposition ( HWCVD) on glass at 250 degreesC with W or Ta wire as the catalyzers. The structual and optoelectronic properties as functions of the filament temperature, deposition pressure and the filament-substrate distance were studied, and the optimized polycrystalline silicon thin films were obtained with X-c > 90 % ( X-c denotes the crystalline ratio of the film), crystal grain size about 30-40nm, R-d approximate to 0.8nm/s, sigma(d) about 10(-7) - 10(-6) Omega(-1) cm(-1), Ea(a) approximate to 0.5eV and E-opt less than or equal to 1.3eV.

High performance of 1.55 mu m DFB integrated with vertically tapered self-aligned spot-size converter

A new type of self-aligned spotsize converter (SSC) integrated 1.55 mum DFB lasers had been proposed in this article. The upper optical confinement layer and the butt-coupled tapered thickness waveguide were regrown simultaneously, which not only offered the separate optimization of the active region and the integrated SSC, but also reduced the difficulty of the butt-joint selective regrowth. The vertical and horizontal far field angles were 9degrees and 12degrees respectively, the 1- dB misalignment tolerance were both 3.6 and 3.4 mum. The directed coupling efficiency to tapered single mode fiber was 48%.

Nanodiamond formation by hot-filament chemical vapor deposition on carbon ions bombarded Si

Nanocrystalline diamond films were grown by a two-step process on Si(1 0 0) substrate, which was first pretreated by pure carbon ions bombardment. The bombarded Si substrate was then transformed into a hot-filament chemical vapor deposition (HFCVD) system for further growth. Using the usual CH4/H-3 feed gas ratio for micro crystalline diamond growth, nanodiamond crystallites were obtained. The diamond nucleation density is comparable to that obtained by biasing the substrate. The uniformly distributed lattice damage is proposed to be responsible for the formation of the nanodiamond. (C) 2002 Elsevier Science B.V. All rights reserved.

Structural evaluation of polycrystalline silicon thin films by hot-wire-assisted PECVD

Tungsten wires were introduced into a plasma-enhanced chemical vapor deposition (PECVD) system as a catalyzer: we name this technique 'hot-wire-assisted PECVD' (HW-PECVD). Under constant deposition pressure (p(g)), gas flow ratio and catalyzer position, the effects of the hot wire temperature (T-f) on the structural properties of the poly-Si films have been characterized by X-ray diffraction (XRD), Raman scattering and Fourier-transform infrared (FTIR) spectroscopy. Compared with conventional PECVD, the grain size, crystalline volume fraction (X-e) and deposition rate were all enhanced when a high T-f was used. The best poly-Si film exhibits a preferential (220) orientation, with a full width at half-maximum (FWHM) of 0.2 degrees. The Si-Si TO peak of the Raman scattering spectrum is located at 519.8 cm(-1) with a FWHM of 7.1 cm(-1). The X-c is 0.93. These improvements are mainly the result of promotion of the dissociation of SiH4 and an increase in the atomic H concentration in the gas phase. (C) 2001 Elsevier Science B.V. All rights reserved.

Microstructures of microcrystalline silicon thin films prepared by hot wire chemical vapor deposition

Undoped hydrogenated microcrystalline silicon (mu c-Si:H) thin films were prepared at low temperature by hot wire chemical vapor deposition (HWCVD). Microstructures of the mu c-Si:H films with different H-2/SiH4 ratios and deposition pressures have been characterized by infrared spectroscopy X-ray diffraction (XRD), Raman scattering, Fourier transform (FTIR), cross-sectional transmission electron microscopy (TEM) and small angle X-ray scattering (SAX). The crystallization of silicon thin film was enhanced by hydrogen dilution and deposition pressure. The TEM result shows the columnar growth of mu c-Si:H thin films. An initial microcrystalline Si layer on the glass substrate, instead of the amorphous layer commonly observed in plasma enhanced chemical vapor deposition (PECVD), was observed from TEM and backside incident Raman spectra. The SAXS data indicate an enhancement of the mass density of mu c-Si:H films by hydrogen dilution. Finally, combining the FTIR data with the SAXS experiment suggests that the Si--H bonds in mu c-Si:H and in polycrystalline Si thin films are located at the grain boundaries. (C) 2000 Elsevier Science S.A. All rights reserved.

TEM study of dislocations in ZnTe/GaAs heterostructure grown by hot-wall epitaxy

A ZnTe layer grown on GaAs substrate by hot-wall epitaxy (HWE) was studied using transmission electron microscopy (TEM). For a (110) cross-sectional specimen, its (001) ZnTe/GaAs interface was analysed by large angle stereo-projection (LASP) and high resolution electron microscopy (HREM). In the LASP, a double diffraction occurred and moire fringes were formed, meanwhile misfit dislocations were revealled clearly by weak beam technique. In HREM, not only Lomer and 60 degrees types of misfit dislocations were observed, but also two types of stacking faults were analysed. The residual strain was estimated by both methods.

Comparison of cooling rates for hot carriers in GaAs AlAs quantum wells based on macroscopic and microscopic phonon models

By using three analytical phonon models in quantum wells-the slab model, the guided-mode model, and the improved version of the Huang-Zhu model [Phys. Rev. B 38, 13 377 (1998)], -and the phonon modes in bulk, the energy-loss rates of hot carriers due to the Frohlich potential scattering in GaAs/AlAs multiple quantum wells (MQW's) are calculated and compared to those obtained based on a microscopic dipole superlattice model. In the study, a special emphasis is put on the effects of the phonon models on the hot-carrier relaxation process when taking the hot-phonon effect into account. Our numerical results show that, the calculated energy-loss rates based on the slab model and on the improved Huang-Zhu model are almost the same when ignoring the hot-phonon effect; however, with the hot phonon effect considered, the calculated cooling rate as well as the hot phonon occupation number do depend upon the phonon models to be adopted. Out of the four analytical phonon models investigated, the improved Huang-Zhu model gives the results most close to the microscopic calculation, while the guided-mode model presents the poorest results. For hot electrons with a sheet density around 10(12)/cm(2), the slab model has been found to overestimate the hot-phonon effect by more than 40% compared to the Huang-Zhu model, and about 75% compared to the microscopic calculation in which the phonon dispersion is fully included. Our calculation also indicates that Nash's improved version [J. Lumin. 44, 315 (1989)] is necessary for evaluating the energy-loss rates in quantum wells of wider well width, because Huang-Zhu's original analytical formulas an only approximately orthogonal for optical phonons associated with small in-plane wave numbers. [S0163-1829(99)08919-5].