Molecular beam epitaxy-grown separate confinement buried heterostructure PbEuSeTe-PbTe diode lasers

Separate confinement buried heterostructure (SCBH) tunable PbEuSeTe-PbTe diode lasers were fabricated by molecular beam epitaxy for the first time. Continuous wave (CW) operating temperature of 215 K was realized, which is the highest CW operating temperature ever reported for lead-chalcogenide diode lasers. Preliminary results show a significant improvement in threshold current and emission power. Exceptionally low threshold currents of 2.5 mA at 120 K, 76 mA at 180 K, and 252 mA at 200 K were measured. The temperature tuning range of the SCBH diode laser spans between 6.49 /spl mu/m at 20 K to 4.19 /spl mu/m at 215 K.     

Characteristics of multistack multiquantum barrier and itsapplication to graded-index separate confinement heterostructure lasers

The enhancement of electron barrier height by multistack multiquantum barrier structure is simulated using the transfer matrix method. The validity and feasibility of this concept is verified by the experimental results on GaAs-AlAs multistack multiquantum barriers. Based on the simulated results, both 0.78 and 1.3 μm graded-index separate confinement heterostructure (GRIN-SCH) lasers with predicted enhanced carrier and optical confinements using graded multistack multiquantum barriers are designed. Lower threshold current, higher modulation bandwidth as well as higher characteristic temperature are expected for these lasers     

MBE growth and characteristics of periodic index separate confinement heterostructure InGaAs quantum-well lasers

We have used solid-source molecular beam epitaxy (MBE) to grow InGaAs quantum-well lasers emitting at 980nm in a novel configuration of periodic index separate confinement heterostructure (PINSCH). Periodic multilayers (GaAs/AlGaAs) are utilized as optical confinement layers to reduce the transverse beam divergence as well as to increase the maximum output power. The multilayers are grown by temperature modulation MBE without any shutter operation. The heterointerfaces in the multilayers are linearly graded such that the energy barrier heights are greatly decreased. This has led to a drastic reduction in the series resistance which is essential in the performance of high output power. The 5μm × 750μm device has far-field angles of 10° by 20°, a threshold current of 45 mA, an external differential quantum efficiency of 1.15 mW/mA (90%), and an output power of 620 mW, all measured at room temperature under CW operation. A record high fiber coupling efficiency of 51% has been achieved and more than 130 mW of power is coupled into a 5μm-core single mode fiber.     

Effect of cladding layer thickness on the performance ofGaAs-AlGaAs graded index separate confinement heterostructure singlequantum-well lasers

The thinning of cladding layers of GaAs-AlGaAs graded index separate confinement heterostructure single quantum-well (GRINSCH-SQW) lasers offers several advantages. These advantages include easier fabrication of surface grating-based lasers and ridge lasers, the reduction of growth time and source-material use, and the more effective removal of heat due to lower thermal resistance. Experimental results from GRINSCH-SQW lasers showing that typical cladding thicknesses of 1.5 to 2 μm are much thicker than necessary are presented. Lasers with cladding layers as thin as 4500 Å have not shown any increase in threshold current. Theoretical analysis shows good agreement with the experimental results on the minimum cladding thickness necessary to prevent an increase in the threshold current. The differential quantum efficiency is theoretically considered and is found to be more sensitive to cladding-layer thickness     

High-power 1.5 mu m all-MOVPE buried heterostructure graded index separate confinement multiple quantum well lasers

A maximum total CW output power of 190 mW has been obtained at 1.55 mu m using a buried heterostructure graded index separate confinement multiple quantum well laser grown entirely by metalorganic vapour-phase epitaxy.<>     

Growth and optimization of extremely high-pulse-power graded-index separate confinement heterostructure quantum well AlGaAs/InGaAs diode lasers with broadened waveguides

Material quality is an essential prerequisite and a major challenge for the fabrication of high-power, 980-nm, strained-quantum-well (SQW) InGaAs lasers. We report our work aimed at metal-organic chemical vapor deposition (MOCVD) growth optimization and epitaxial quality analysis of various graded-index separate confinement heterostructure (GRINSCH) QW AlGaAs/InGaAs laser structures. Systematic investigation of doping level control and minimization of oxygen incorporation in AlGaAs were performed. Background oxygen levels of 10¹⁵ cm⁻³ were obtained with n-(Si) and p-(C) doping concentrations as high as 1 × 10¹⁸ cm⁻³ and 3 × 10¹⁸ cm⁻³, respectively, for Al_0.4Ga_0.6As layers. Double-crystal x-ray (DCXR), room-temperature photoluminescence (PL) mapping, Hall effect measurements, and secondary ion-mass spectroscopy (SIMS) techniques were used to evaluate material quality. A record, multimode, pulsed output power of 52.1 W has been obtained from 100-μm × 2-mm broad-stripe lasers made from these materials. The devices demonstrate low threshold current, low cavity losses, and kink-free light-current characteristics.     

Influence of separate confinement heterostructure on emission bandwidth of InGaAsP superluminescent diodes/semiconductor optical amplifiers with nonidentical multiple quantum wells

Experiments show that the layer of separate confinement heterostructure (SCH) has a significant influence on the emission spectrum of superluminescent diodes (SLDs)/semiconductor optical amplifiers (SOAs). Reducing the thickness of SCH layer at the p-side could improve the uniformity of carrier distribution among multiple quantum wells (MQWs). With three In/sub 0.67/Ga/sub 0.33/As/sub 0.72/P/sub 0.28/ QWs near the p-side and two In/sub 0.53/Ga/sub 0.47/As QWs near the n-side, when the thickness of the SCH layer changes from 120 to 30 nm, the operation current for SLDs/SOAs to exhibit the full-width at half-maximum spectral width of above 270 nm could be reduced from 500 to 160 mA.     

Small-area GaAs-GaAlAs heterostructure light-emitting diode with improved current confinement

A new type of high-radiance GaAs-GaAlAs heterostructure light-emitting diode (l.e.d.) with confinement of the light-emitting area by contact resistance is described. Single heterostructure l.e.d.s of this type with active-region doping of p=3×1018 cm?3 exhibit external quantum efficiency of 1% and a 3 dB modulation cutoff frequency of 66 MHz. Second-harmonic distortion was measured at below 40 dB at a 30 mA peak-peak modulation current and 50 mA direct current (=7.0 kA/cm2).     

A novel separate lateral confinement quantum-well heterostructurelaser

Utilizing separate structures for the lateral confinement of the optical mode and injected carriers, we optimize the overlap of the optical mode with the gain to demonstrate lasers with lower threshold currents than standard ridge waveguide lasers     

Lasing characteristics of distributed-feedback GaAs-GaAlAs diode lasers with separate optical and carrier confinement

The lasing characteristics of separate-confinement-heterostructure (SCH-structure) distributed-feedback (DFB) diode lasers are examined theoretically and experimentally. Wave propagation in five-layer SCH waveguides is analyzed to estimate such parameters as the lasing wavelength, coupling constant, and external quantum efficiency. Spectral and modal behavior are studied in the experiment and compared with the theoretical predictions. Diodes are shown to lase in a single longitudinal mode with a definite polarization. Spectral width is about 300 MHz just above the threshold, and becomes wider with increased excitation level. An output power of 40 mW with an external quantum efficiency of 5 percent is obtained under CW operation.     

Nanoscale light confinement and transport in symmetric hybrid plasmonic waveguides based on silicon nanoslots

正Light confinement at the nanoscale beyond the fundamental diffraction limit is of critical importance to the advancement of next-generation photonic technology,since it offers unprecedented opportunities with dramatically enhanced light-matter interactions.A silicon-nanoslot based symmetric hybrid structure was reported,capable of providing low propagation loss,subwavelength mode size and tight field confinement inside the low-index gap region.The nice optical performance in conjunction with several unique features could enable a number of further applications.In addition to the waveguide proposed here,a number of alternative guiding schemes could also be employed to achieve the goal of propagation loss reduction with subwavelength mode confinement,including structures based on horizontal slot waveguides,and many other configurations capable of forming symmetric or near-symmetric environment along with high-index contrast near the metallic waveguides,such as metal nanostructures covered by low-high-index dielectrics supported by low-index substrates,and coaxial type-structures consisting of metallic nanowires surrounded by dielectrics.     

Sensitivity comparison of symmetric and asymmetric dual-mode bandpass filters

Sensitivity analysis of dual-mode filters shows: (a) approximately the same sensitivities for the symmetric and asymmetric realisations; (b) a trend that the further the physical cavity from the input/output ports, the higher is its sensitivity. These findings should help in the design of dual-mode filters for spacecraft application.     

Stimulated emission and optical gain in CdTe/CdMnTe graded index separate confinement heterostructures

Stimulated emission and optical gain in CdTe/CdMnTe graded index separate confinement quantum wells have been investigated as a function of optical excitation powers and temperatures. Maximum gain of about 100 cm^-1 is obtained at 95K for a single quantum well under 2-3 kW/cm² excitation. This value allows to design laser cavities compatible with the microgun pumped laser device concept. The temperature dependence of the gain still remains a problem (T₀ = 110K).     

1.3 μm multiquantum well decoupled confinement heterostructure(MQW-DCH) laser diodes

A 1.3-μm multi-quantum-well decoupled confinement heterostructure (MQW-DCH) laser diode has been developed. This structure introduces internal barriers between the active quantum wells and the optical waveguide. It is thus possible to have, at the same time, deep quantum wells to prevent carrier leakage and a strong optical waveguide with a high confinement factor. The barrier parameters have been optimized using numerical modeling tools, and the DCH laser diode has been built using chemical beam epitaxy. The broad-area transparency current density is 140 A-cm^-2, the internal efficiency is 0.83, the waveguide loss is 5 cm^-1. and T₀ = 62 K. Ridge waveguide laser diodes have a room temperature threshold of 8 mA and an efficiency of 0.32 mW/mA     

1.3 mu m GaInAsP/InP buried heterostructure graded index separate confinement multiple quantum well (BH-GRIN-SC-MQW) lasers entirely grown by metalorganic chemical vapour deposition (MOCVD)

Reports the first successful demonstration of a 1.3 mu m GaInAsP/InP buried heterostructure graded index separate confinement multiple quantum well laser (BH-GRIN-SC-MQW LD) entirely grown by three-step low pressure metal-organic chemical vapour deposition (LP-MOCVD). The threshold current and the differential quantum efficiency were 31 mA (threshold current density 3.4 kA/cm/sup 2/) and 28%/facet, respectively. A characteristic temperature of 65 K was obtained.<>     

Modelling of parameters for asymmetric halo and symmetric DHDMG n-MOSFETs

This article presents an analytical surface potential, threshold voltage and drain current model for asymmetric pocket-implanted, single-halo dual material gate and double-halo dual material gate (DHDMG) n-MOSFET (MOSFET, metal–oxide–semiconductor field-effect transistor) operating up to 40?nm regime. The model is derived by applying Gauss's law to a rectangular box, covering the entire depletion region. The asymmetric pocket-implanted model takes into account the effective doping concentration of the two linear pocket profiles at the source and the drain ends along with the inner fringing capacitances at both the source and the drain ends and the subthreshold drain and the substrate bias effect. Using the surface potential model, the threshold voltage and drain currents are estimated. The same model is used to find the characteristic parameters for dual-material gate (DMG) with halo implantations and double gate. The characteristic improvement is investigated. It is concluded that the DHDMG device structure exhibits better suppression of the short-channel effect (SCE) and the threshold voltage roll-off than DMG and double-gate MOSFET. The adequacy of the model is verified by comparing with two-dimensional device simulator DESSIS. A very good agreement of our model with DESSIS is obtained proving the validity of our model used in suppressing the SCEs.     

Thermoelectric properties of symmetric and asymmetric double quantum well structures

The electronic states and carrier transport in (100)PbTe/Pb _{1 ? x} Eu _x Te double quantum wells are theoretically analyzed. The dependences of the mobility and Seebeck coefficient on the thickness of the internal barrier in symmetric and asymmetric structures are investigated. It was found that at great distance between the wells even small violation of the structure symmetry and essential reconstruction of electron wave functions results in suppression of intersubband scattering with carriers transfer between the wells and provides the correct limit to isolated quantum well in kinetic coefficients. Some possibilities of increasing the thermoelectric power factor are found, and a suitable set of structure parameters is calculated within the proposed model.     

An analytic potential model for symmetric and asymmetric DG MOSFETs

This paper presents an analytic potential model for long-channel symmetric and asymmetric double-gate (DG) MOSFETs. The model is derived rigorously from the exact solution to Poisson's and current continuity equation without the charge-sheet approximation. By preserving the proper physics, volume inversion in the subthreshold region is well accounted for in the model. The resulting analytic expressions of the drain-current, terminal charges, and capacitances for long-channel DG MOSFETs are continuous in all operation regions, i.e., linear, saturation, and subthreshold, making it suitable for compact modeling. As no fitting parameters are invoked throughout the derivation, the model is physical and predictive. All parameter formulas are validated by two-dimensional numerical simulations with excellent agreement. The model has been implemented in Simulation Program with Integrated Circuit Emphasis version 3 (SPICE3), and the feasibility is demonstrated by the transient analysis of sample CMOS circuits.