Predicted performance of quantum-well GaAs-(GaAl)As opticalamplifiers

The gain, noise, and saturation performance of GaAs-(GaAl)As quantum-well laser amplifiers is calculated. A single-quantum-well amplifier with 100-mA injection should achieve similar gains to those of present devices with bulk active regions, but with improved saturation output powers and near-ideal noise performance. A low-current amplifier with a 2.5-mA injection current is investigated for varying well thickness and number of wells     

D_2~ 轰击隔离条形(GaAl)As/GaAs双异质结构激光器

在室温至600℃退火D_2~ 轰击过的GaAs单晶片,只要退火温度低于200℃,得到的电阻率可达(1～2)×10~8欧姆·厘米。用D_2~ 轰击(GaAl)As/GaAs双异质结构片,制成的隔离条形激光器,近场、光谱、频率响应及退火等特性都与H~ 轰击激光器差不多。     

Fundamental transverse and longitudinal mode oscillation in terraced substrate GaAs-(GaAl)As lasers

A new, simple structure for a stripe-geometry laser is proposed. A double heterostructure is fabricated on a terraced substrate, providing a modified rib-waveguide structure in the active layer. A lasing mode is confined and stabilized in the narrow area between two adjacent bends of the active layer. The terraced substrate laser exhibits a stable, single longitudinal mode oscillation as well as a fundamental transverse mode oscillation in CW operation. No kinks have been observed in light-output versus current characteristics. The linearity continues up to ten times the threshold in the pulsed operation at which the power output is 150 mW per facet.     

(GaAl)As/GaAs质子轰击隔离条形DH激光器的退化原因

对研制的(GaAl)As/GaAs质子轰击隔离条形DH激光器的退化原因进行了实验分析。结果表明:快退化主要起因于有源区内的暗点、暗线及暗区等缺陷的增殖;腔面氧化是限制寿命在千小时的原因之一;质子轰击引入的点缺陷移入有源区是器件限制寿命在万小时的原因之一。     

Dual-wavelength (GaAl)As laser

A monolithic structure integrating two stripe-geometry (GaAl)As lasers emitting at 8500 and 8850 ? is described. The threshold currents for both lasers are in the 50?70 mA range. The spacing between the stripes for the device reported here is 25 ?m; it can be reduced to 10 ?m in order to optimise the direct coupling to a 50 ?m diameter fibre.     

Valence band mixing and optical emission in modulation-doped GaAs-(AlGa)As heterostructures

Unexpected optical emission spectra from electrons confined in GaAs quantum layers reveal a strong component with polarization normal to the plane of the layers. For elementary electron-hole recombination processes, this suggests surprisingly large band mixing in the ground valence subband. Effective mass theories that include conventional symmetry breaking mechanisms do not satisfactorily account for this phenomenon. The stress dependence of the spectra confirm that many body shake-up processes in the Fermi sea are important in describing emission associated with the 2D electron plasma.     

High-reflectivity cavity mirrors for high-performance (GaAl) As diode lasers

Effects of the high-reflectivity mirrors on the performance of (GaAl)As diode lasers are investigated by using a laser diode model. An optimum value for the mirror reflectivity is obtained by using a figure of merit which reflects low threshold and high slope efficiency. An optimum reflectivity valueR = 0.75is obtained for a laser with a cavity lengthl= 300 mum and an internal loss coefficientgamma_{i} = 10cm^-1. A higher internal photon flux density relative to the output photon flux density is shown to occur with the high-reflectivity mirror. High-reflectivity mirrors are shown to reduce optical feedback effect from external devices and the lowered threshold value to reduce the thermal effects on the modulation characteristics and the degradation.     

Negative photocurrent in GaAs-(AlGa)As heterojunctions

A negative photoresponse in p lightly doped GaAs-n heavily doped (AlGa)As heterojunctions is observed. The a.c. spectral response is presented as a function of d.c. bias and illumination. A model for negative photocurrents is proposed as due to electron diffusion into the p side. The photoresponse sign reversal is caused by the existence of the notch-spike discontinuity and of a notch population. Estimations of the band diagram are made from photoresponse and electrical measurements.     

A new monolithic composite- cavity (GaAl)As laser

A new composite-cavity (GaAl)As laser comprising a monolithically integrated pair of a laser and reflector has been developed on the basis of the chemical etching technique reported by the present authors. The rear facet of the laser and the reflector are separated by a small air gap. As a result, the new laser showed low threshold and high mode stability operation without mode jumping in a temperature range as wide as 25°C.     

Optimization and characterization of high-radiance (Al,Ga)As double-heterostructure LED's for optical communication systems

Phenomenological models for Burrus-type high-radiance double-heterostructure LED's are described which make it possible to calculate the maximum optical power emitted from a diode chip, the equilibrium optical power coupled into an optical fiber of a given numerical aperture NA and core diameter, and the transient response of the spontaneous emission of the LED, and afford criteria for optimization of these devices. Measured values of power and rise time are found to agree with theory to a useful degree of approximation. Reliability data for optimized LED's are presented.     

Radiation fields of GaAs-(AlGa)As injection lasers

Theoretical radiation patterns from a multilayer model of a dielectric waveguide are fitted to single mode experimental profiles of three symmetrical double-heterojunction cavities to test the adequacy of the model and study the effect of the dielectric parameters on the beam pattern. The radiation from the normal TE modes is approximated by plane waves, while for the TM modes it is given by boundary value solutions of the Maxwell equations. The adequacy of the theory is shown by the faithfulness of the fit out to large beam angles and low intensities, and the agreement of the adjusted cavity parameters to the experimental values. Small changes in either the cavity thickness or the dielectric constant of the internal n-type region have similar first order effects on the angular position of the minima in the profile as well as in the amplitude of the sidelobes. Depths of the minima decrease with departures of the structure from planarity. Pattern distortion from mode coupling at the interfaces and facets is not observed.     

A stabilized zinc diffused-proton bombarded (GaAl)As laser

A new (GaAl)As stripe laser in which a refractive index step is created by a zinc diffusion on both sides of a conventional proton stripe structure, called a diffused bombarded stripe (DBS) laser, is presented. This diffusion provides passive transverse guiding with a relatively simple technology. The index step can be adjusted by controlling the diffused zinc concentration in relation to the active region doping level. A self-alignment technique for the diffused and bombarded stripes reduces the current leakage through the diffused regions. Lasing threshold currents as low as those of conventional proton stripe lasers are obtained. A significant improvement of light-current linearity, transverse mode stability and longitudinal mode structure are observed with the DBS lasers.     

An Analytical Solution of the Lateral Current Spreading and Diffusion Problem in Narrow Oxide Stripe (GaAl)As/GaAs DH Lasers

An exact solution is presented to the problem of lateral current spreading in the resistive layer of oxide stripe geometry DH lasers. The two-dimensional Laplace equation was solved by conformal mapping using the Schwarz-Christoffel transformation. The diffusion equation containing nonlinear recombination terms was solved numerically. Computed examples demonstrate that the customary one-dimensioned treatment of the resistive layer or the assumption of constant current density under the stripe contact are not always justified, particularly for narrow stripe widths and low specific resistivities. This region of low values of the resistivity and stripe width, however, is of great practical interest in the design of oxide stripe lasers having high thermal stability and kink-free characteristics.     

Low threshold Be implanted (GaAl)As laser on semi-insulating substrate

Be implanted stripe geometry double heterostructure lasers have been fabricated on a semi-insulating GaAs substrate, with threshold currents as low as 15 mA for a cavity length of 100 μm. The laser has been monolithically integrated with a metal-semiconductor field-effect transistor.     

High-speed high-power 1.3-µm InGaAsP/InP surface-emitting LED's for short-haul wide-bandwidth optical-fiber communications

High-speed high-power double-heterostructure 1.3-µm InGaAsP/InP LED's have been developed for use in short-haul wide-bandwidth fiber-optics systems. At 150-mA dc, devices typically launch - 11.7 dBm into a 62-µm core graded index (GI) fiber. Optical bandwidth is typically 690 MHz with a 50-mA prebias. Modulation capability was demonstrated at 1-Gbit/s NRZ with - 15.7 dBm of peak power launched into the fiber. Rise and fall times of 340 and 780 ps, respectively, were achieved. Reliability data indicates a median life of ∼ 10⁸h for anticipated operating conditions.     

Voltage comparators implemented with GaAs/(GaAl)As heterojunction bipolar transistors

The first voltage comparators implemented with GaAs/(GaAl)As heterojunction bipolar transistors (HBTs) are reported. The offset voltage of these circuits was found to be generally below 4 mV, and hysteresis below 1 mV; both voltages stayed quite constant over a range of reference voltage of about 1 V. The preliminary circuit yield was high. This work demonstrated the suitability of these HBT comparators for use in a flash A/D convertor of high accuracy (up to 8 bits).     

(GaAl)As/GaAs heterojunction bipolar transistors with graded composition in the base

The first fabrication and high-speed operation of a three-terminal (AlGa)As/GaAs heterojunction bipolar transistor with graded bandgap base is reported. Cutoff frequencies up to 16 GHz have been achieved in devices fabricated from material made by molecular beam epitaxy. This work demonstrates the feasibility of using a graded (AlGa)As base to enhance the speed of heterojunction bipolar transistors.     

An analytic study of (GaAl)As gain guided lasers at threshold

An analysis of gain-guided diode lasers at threshold is presented. After describing the formulation, the effects of charge induced real refractive index antiguiding and gain-charge density relations are studied in detail. Their influence on the threshold current, modal distributions, and the lateral fax-field radiation patterns is discussed. Next a "model" laser is defined and each parameter including dimensions, compositions, stripewidth, diffusion constants, current spreading resistance, and facet reflectivities is individually varied to determine the resulting modifications in laser properties.     

An improved liquid-phase-epitaxial growth method for GaAs-(Ga, Al)As double heterostructures

A new growth method of GaAs-(Ga, Al)As multilayer, in which the solid surface is always covered by a melt during the growth of multilayer, is proposed, and laser characteristics of wafers grown by this method are presented.     

A new chemical etching technique for formation of cavity facets of (GaAl)As lasers

A new chemical etching technique which offers excellent cavity facets of Ga1-xAlxAs lasers is reported. This technique is based on our finding that the crystallographic anisotropy in the conventional etching process of Ga1-xAlxAs multilayers depends strongly on the AlAs mode fractionxin every layer. A suitable combination of the mole fractions in the multilayer is therefore a key factor for obtaining practically vertical walls with sufficient smoothness and flatness as laser cavity facets. In fact, the reflectivity of the etched facet obtained is 28 percent, being compatible to that in the conventional cleaved facets. As a result, a CW operation with threshold current as low as 28 mA and external quantum efficiency as high as 24 percent per facet has been attained with high reproducibility.