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.     

Spike-notch structure of (AlGa)As heterojunctions

The I-V characteristics and optical properties of (AlGa)- As p-n heterojunctions, with a larger bandgap on the n side, were studied. The discontinuity of conduction bands, tilted by the space-charge electric field, produces a spike-notch structure. At comparable low doping levels on both sides of the heterojunction, the notch is empty at zero-bias conditions and acts as a trap for injected electrons. Thermal injection into the p-type region becomes the predominant current mechanism after the notch has been filled with electrons. The notch population is a step function of the applied voltage and determines an S-shaped I-V characteristic. Radiative recombination and ac photocurrent under dc bias gives further support for the existance of captured electrons in the notch.     

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-power (AlGa)As strip-buried heterostructure lasers

The characteristics of index-guided strip-buried heterostructure lasers are described. The lasers are grown by a two-step process, consisting of the initial 5-layer planar growth by MOCVD, and after etching to define the strip buried wave guide, recovery by Al0.65Ga0.35As using LPE. The devices are highly uniform, having 20 mA thresholds, quantum efficiencies of 0.65, and T0of 163°C. The TE polarized emission was in the lowest order transverse mode and consisted of ∼ 6 longitudinal modes. CW output powers of 50 mW per facet were obtained from lasers with reduced output reflectivity, and pulsed powers of 95 mW per facet from uncoated lasers have been obtained. The far-field angular widths weresim 23degandsim 50degin, and perpendicular to the junction plane, respectively. The total optical conversion efficiency of the coated laser emitting 50 mW CW was 41.5 percent.     

Degradation in short wavelength (AlGa)As light-emitting diodes

Degradation in short-wavelength (AlGa)As lasers is investigated through lifetests of such devices operated in the incoherent mode. It is shown that degradation increases with emission energy for diodes containing zinc in the p-type (AlGa)As bounding region, whereas diodes containing Ge in this region, although not satisfactory as c.w. lasers because of high resistivity, show no degradation. A way out of this difficulty is proposed through double doping with Ge and Zn, in which case degradation appears to be brought down to the Ge level.     

Gain mechanism in an (AlGa)As double heterostructure laser

Presented here is substantial evidence of a specific quantum mechanical model for gain in a (AlGa)As double heterostructure laser with a pure active layer. Close quantitative agreement between predicted and measured values substantiates a new model that evolves directly from Stern's theory. A novel method employing picosecond optical probe pulses coupled axially to the semiconductor laser gain guide allows the first direct measurements of guide gain. The concept of optical impulse response is introduced. Current spreading and facet reflectivity are directly measured. The first self-consistent set of characteristic parameters for a specific laser are determined.     

(AlGa)As可见光激光器的镜面保护

本文介绍了一种可见光激光器端面镜面保护方法。用电子束蒸发在可见光激光器的两个镜面上分别镀上0.75 λ/2和λ/2厚的 Al_2O_3钝化膜,并就镀膜对激光器性能的影响进行了测试研究。经过镜面保护的可见光激光器寿命有很大改善,且由于一个端面镀上0.75 λ/2抗反射膜,使激光器的极限输出功率有一定的提高。     

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     

The reliability of (AlGa)As CW laser diodes

This paper reviews the major factors bearing on the reliability of (AlGa)As CW laser diodes. The degradation modes of facet mirror damage, contact degradation, and internal damage are discussed in terms of our present knowledge of their effects on device performance, their origin, and their reduction or elimination. Detailed results are presented for oxide-defined stripe-contact lasers and, although reliability results are a strong function of fabrication technology, there are many issues common to all fabrication technologies, and these are emphasized. Lasers have been operated in our laboratory for more than 40 000 h with extrapolations indicating a median time to failure (MTTF) between 10⁵and 10⁶h. In these lasers both facet damage and contact degradation appear to be under control and internal damage remains the dominant failure mechanism. While still not well documented, for internal damage a so called "activation energy" of 0.7 eV may be useful for high temperature accelerated lifetests. Most of the reliability data deals with threshold current increase, however, shifts in far-field pattern and changes in laser modulation characteristics, such as self-sustained oscillations, may affect laser performance in real systems.     

Analysis of rapid degradation in high-power (AlGa)As laser diodes

A multitemperature accelerated life test conducted to determine the lifetime and reliability of semiconductor lasers for long-term space applications is discussed. The primary cause of failure during two of these life tests (heat sink temperatures of -20°C and 50°C, respectively) was identified as carbon contamination on the front facet resulting in an initially rapid but saturable decrease in output power. The carbon contamination on the facet was the sole cause of the decrease in power for most of the laser diodes from the -20°C test. Removing the sources of carbon from the laser diodes eliminated the front facet degradation, and this resulted in increased laser diode lifetime in subsequent life tests. The index of refraction and the absorption coefficient of the contamination found on the laser diodes from the -20°C test were calculated. the resulting values compared favorably with those reported by other researchers for amorphous hydrogenated carbon     

InGaAs/In(AlGa)As RHET's with InAs pseudomorphic base

An InGaAs/In(AlGa)As resonant-tunneling hot-electron transistor (RHET) with an INAs pseudomorphic base to increase current gain and to reduce base resistance was designed and fabricated. The conduction band discontinuity between the InAs base and the In(AlGa)As collector barrier was estimated from the thermionic current. The band discontinuity was about 0.38 eV, which agrees well with the calculated band discontinuity taking into consideration the effect of strain. The common-emitter current gain doubled and the base resistance decreased 20% compared to InGaAs-base RHETs with the same doping concentration. A current gain cutoff frequency of 65 GHz and a maximum oscillation frequency of 50 GHz at 77 K were measured     

A new edge-emitting (AlGa)As heterojunction LED for fiber-optic communications

A new edge-emitting structure designed for fiber-optical communications, in which the active area is limited to the edge of the chip, is described. Significant improvements in the quantum efficiency compared to previous emitting structures are obtained. A power emission of 2 mW for one edge is obtained at a current of 250 mA (λ = 8000 Å).     

(AlGa)As strip buried-heterostructure lasers prepared by hybrid crystal growth

The localised nonwetting problem encountered during regrowth by LPE in the fabrication of a strip buried-heterostructure (SBH) laser was solved by using the hybrid process of MBE to grow the uniform four-layer heterostructure and LPE to achieve the melt back and regrowth. As a result of this process, a very significant improvement in the device yield was obtained.     

High-frequency signal recording on film using (AlGa)As CW injection lasers

CW injection lasers have demonstrated excellent performance when used in a wide-band film recorder. These lasers have been internally modulated from 1 to 200 MHz (±2 dB) and film recordings of signal frequencies up to 100 MHz (160 cycles/mm) have been made.     

Nonlinearities in the emission characteristics of stripe-geometry (AlGa)As double-heterostructure junction lasers

Significant changes in the optical and electrical properties of stripe-geometry (AlGa)As double-heterostructure junction lasers have been observed to accompany a nonlinearity in the current dependence of the lasing emission. Over the nonlinear range, the optical field of the lasing emission shifts continuously with current toward one boundary of the active stripe. Simultaneously, effective gain saturation is lost and additional transverse modes are excited. The increasing gain is believed to occur primarily in spatial regions where the optical intensity is reduced as a result of the transverse motion of the field. Additional observations suggest that this transverse motion results from an interaction between the intense lasing field and the active medium. Consequently, gain depletion is discussed as a possible cause for the transverse instability. Implications of this model for a qualitative understanding of the improved output performance recently obtained from lasers with narrow stripes are also considered.     

Self longitudinal-mode stabilisation in GaAs/(AlGa)As quantum-well lasers

Single-longitudinal-mode operation of zero-order lateral mode quantum-well GaAs/(AlGa)As Fabry-Perot lasers has been found to occur over a very wide operating current range. Single-longitudinal-mode operation is very stable, typically allowing an increase in optical output power from 0 to >20mW/facet before mode-hopping occurs. The mode hop at ~23mW leads to bistable single-longitudinal-mode operation with a very large hysteresis loop.     

On the low-temperature degradation of (AlGa)As/GaAs modulation-doped field-effect transistors

A comprehensive study of the anomalous low-temperature behavior of modulation,doped (Al, Ga)As/GaAs field-effect transistors is reported, Experiments on the effect of bias stress on the current-voltage characteristics in lateral resistors, 1-µm gate FET's, and a novel dual-gate tester are presented along with the results of freeze-out, optical spectroscopy, and trapping kinetics experiments. Both modulation-doped (Al, Ga)As/GaAs heterostructures and isolated (Al, Ga)As layers are examined. The results delineate the conditions under which threshold shift andI-Vcollapse occur. Based on these results a detailed physical model which explains these effects is proposed. One important conclusion of this work is that the collapse is not related to hot electron injection from the high mobility channel, as suggested earlier, but is a property of a highly doped AlGaAs layer under bias.     

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.     

Self-consistent particle simulation for (AlGa)As/GaAs HBTs withimproved base-collector structures

A one-dimensional self-consistent particle simulation was developed for (AlGa)As/GaAs heterojunction bipolar transistors (HBTs) to investigate how far device performance can be improved by positively utilizing nonequilibrium electron transport phenomena. Hole plasmon scattering and the screening effect on LO phonon scattering were proved to play an essential role in determining the minority-carrier temperature in a heavily doped base layer. The computation was carried out for HBTs with various types of base and collector structures. The electron transport mechanisms are discussed in detail in connection with the reduction in base-to-collector transit time. Intrinsic device performance is expected to improve with the cutoff frequency exceeding 150 GHz, as a result of adopting a graded-gap base and a p-type collector structure, even under a heavily doped base condition