Near-infrared high-power LED's with Ga1-xAlxAs epitaxially grown junctions

This paper reports on a study of several techniques of fabricating an efficient Ga1-xAlxAs IRED with high power. Smooth epitaxial layers are grown on a substrate containing a thick Ga1-xAlxAs epitaxial layer which is used to form a hemispherical emitting surface. This is achieved by using a melting-back technique without up-heating. An effect of the AlAs molefraction ratio between n- and p-type regions was clearly found by measurement of a large number of diode chips, and the best performances were obtained on the junctions with the ratioX_{n}/X_{p} simeq 1.5. Ohmic contacts to the p and n regions were applied on the same surface of the wafer using only one metallic source for the vacuum deposition. A cerium-oxide film serves as an antireflection coating when deposited on the hemispherical surface and increases the optical output power by more than 30 percent. External quantum efficiencies of 28 percent (current density: 400 A/ cm²) and optical output power of 96 mW (drive current: 300 mA, current density: 1500 A/cm²) have been observed from diodes emitting at 8300 Å under dc operation at room temperature.     

A Ga1-xAlxAs monolithic opto-isolator

The performance of a Ga1-xAlxAs monolithic opto-isolator incorporating identical emitter and detector structures is described. The device is fabricated from graded bandgap Ga1-xAlxAs grown by liquid phase epitaxy on a semi-insulating GaAs substrate. Three identical rectangular diode elements are fashioned on the chip; the center element acts as an edge-emitting LED and the outer two bars serve as edge-receiving photodiodes. Air-isolated prototype structures possess optical coupling nearly comparable to typical hybrid devices, and this coupling will be improved by dielectric isolation. Isolation voltages between the LED and the detector exceed 1400 volts. The devices achieve excellent performance in both digital and analog signalling tests.     

GaAs MESFET's with Ga1-xAlxAs buffer layers

MESFET's were fabricated with GaAs active layers and Ga1-xAlxAs buffer layers grown by metallorganic vapor-phase epitaxy on semi-insulating substrate Ga1-xAlxAS buffer layers with x = 0.2, 0.4, and 0.6 were used to determine the effect of buffer-layer composition on device performance. While very high transconductance values (175 mS/mm) were obtained with buffer layers with x = 0.2, the transconductance decreased with increase of aluminum composition in the buffer layer. The decrease in transconductance may be due to an observed reduction of electron mobility in the active layer with increasing aluminum concentration in the buffer layer.     

Frequency response of Ga1-xAlxAs light-emitting diodes

Frequency responses of Ga1-xAlxAs light-emitting diodes with various Al composition are measured. When the emission peaks become shorter than 7000 Å, the cutoff frequencies decrease abruptly from 15 MHz to 5 MHz. A conclusion is that the frequency response is determined mainly by the lifetime of injected electrons which changes along with the Al composition because of the distribution of electrons between the Γ and X valleys.     

The reliability of a practical Ga1-xAlxAs laser device

A GaAlAs DH-laser hybrid device is described that compensates for temperature variations and laser degradation. Lifetesting in a 55°C ambient for over a year yields a projected room-temperature median lifetime of6 times 10^{5}h. Lasers having no aluminum in the active layer have a median lifetime 70 times smaller.     

Stimulated emission from Ga1-xAlxAs diodes at 77°K

Ga1-xAlxAs was found to be a suitable material for semiconductor lasers. Stimulated emission from Fabry-Perot type of diodes has been observed at 77°K and 273°K. The highest peak energy of the laser line at 77°K so far is 1.65 eV (l = 7500Å). The Ga1-xAlxAs material was obtained by a liquid phase epitaxial method, described in a previous paper.     

Impact ionization in Ga1-xAlxSb: An alternative interpretation

The existence of the recently proposed resonance impact ionization process in gallium aluminum antimonide is questioned. An alternative interpretation of the data originally used to support the claim for a resonant process is presented which invokes only conventional, well-established processes.     

Preparation and properties of Ga1-xAlxAs-GaAs heterostructure lasers grown by metalorganic chemical vapor deposition

Recently Ga1-xAlxAs-GaAs double-heterostructure lasers having low threshold current densities have been grown by metalorganic chemical vapor deposition. In addition to these conventional double-heterostructure lasers, unique laser structures have been grown, e.g., channel-guide, distributed-Bragg-confinement, and single- and multiple-quantum-well lasers. We describe here the preparation and performance of these devices.     

Temperature behavior of bright luminescence from LPE-grown Ga1-xAlxP structures

Luminescent properties of LPE-grown Ga1-xAlxP (0 leq x geq 0.3) structures have been studied over a wide temperature range. The complicated character of low-temperature luminescence is attributed to intrinsic and impurity-related recombination. The essential dependence of free exciton recombination upon temperature and composition is established for radiative Ga1-xAlxP structures. Anomalous and normal dependence of radiative efficiency on temperature has been shown to be characteristic of intrinsic and impurity-related luminescence. Thus the temperature dependence of the total luminescence can be controlled simply by varying the donor impurity doping level. LED's with luminous intensityI_{V}= 2mcd atT = 300K have been fabricated from the LPE-grown Ga1-xAlxP p-n structures which have high temperature stability of injection and breakdown luminescence efficiency, and emission band spectral position.     

A computer analysis of Ga1-xAlxAs-GaAs solar cells with multilayered window structure

Numerical calculations have been made of the spectral response and conversion efficiency of Ga1-xAlxAs-GaAs solar cells with multilayered window structures. Maximum conversion efficiencies of about 20 percent are predicted, equaling those achieved with graded band-gap solar cells, for the case of three-layered window structures.     

Ga1-xAlxSb avalanche photodiodes: Resonant impact ionization with very high ratio of ionization coefficients

The liquid-phase epitaxy and device fabrication of p-n and p-i-n Ga1-xAlxSb avalanche photodiodes is described. Breakdown voltages up to 95 V and dark currents of 10^-4A/cm²have been obtained. With p-i-n diodes we have measured the impact ionization coefficients α (electrons) and β (holes) with different composition and temperature. A resonant enhancement of the hole ionization coefficient is found forx = 0.065(300 K) where the ratiobeta/alphaexceeds values of 20. This effect is attributed to impact ionization initiated by holes from the split-off valence band: if the spin orbit splitting Δ is equal to the bandgap energy Eg, the threshold energy for hole initiated impact ionization reaches the smallest possible value (E_{i} = E_{g}) and the ionization process occurs with zero momentum. This leads to a strong increase of β atDelta/E_{g} = 1. The experimentally determined dependence of ionization coefficients on threshold energy is compared with theoretical expectations.     

Measurement of minority carrier lifetime during gradual degradation of GaAs-Ga1-xAlxAs double- heterostructure lasers

Minority carrier lifetime in the active layer of GaAs-Ga1-x- AlxAs double-heterostructure lasers has been found to decrease during gradual degradation by measuring the lasing delay time. This phenomenon is ascribed to a decrease in the internal quantum efficiency. Furthermore, a development of the inhomogeneity in the active layer is deduced from observations of the change of near-field patterns, light intensity versus current characteristics, and photoluminescence patterns.     

Band offset effect on transport in AlxGa1-xAs/GaAs heterojunction bipolar transistors grown by metalorganic chemical vapor deposition

AlxGa1-xAs/GaAs heterojunction bipolar transistors were grown with x in the emitter from 0 to 0.57 and the band offset effect on electron transport has been studied using a new technique. The data, though preliminary, indicate that the transport is dominated by electrons near the conduction-band minima when x < 0.45, but not when x = 0.57.     

A detailed investigation of the D-X center and other trap levels in GaAs-AlxGa1-xAs modulation-doped heterostructures grown by molecular-beam epitaxy

We have re-examined the results and analysis of capacitance transient spectroscopy measurements made on modulation-doped heterostructures suitable for the fabrication of field-effect transistors. It is seen that conventional analysis of data can lead to erroneous results and a new model, which includes the contribution of the capacitance at the heterointerface, is presented. Most of the observed anomalous behavior related to trap emission can now be explained. Six main electron traps are present in single-layer AlxGa1-xAs, grown by molecular-beam epitaxy, and in device-quality GaAs-AlxGa1-xmodulation-doped heterostructures. These range in energy from 0.40 to 0.91 eV in thermal ionization energy. The well known D-X center in Si-doped AlxGal-xAs layers is composed of two closely spaced levels, DX1 and DX2, with ionization energies of 0.48 and 0.52 eV, respectively. At very low Si,doping levels, only DX2 is dominant, but at doping levels > 10¹⁸cm^-3, both DX1 and DX2 become comparable in concentration. The optical ionization properties of these levels were also measured and it is seen that the optical lineshapes differ markedly for the two centers. The peak photoionization cross sections occur at spectral energies of 1.25 and 1.38 eV for DX1 and DX2, respectively. The nature and symmetry of the centers have been studied by measurements on layers of different orientations.     

椭圆软波导组件功率容量提升的工程研究

作为常用的雷达系统中馈线元件椭圆软波导组件在工程应用中易出现空气击穿问题很少提及,本文通过对输入驻波的频带特性和调谐螺钉的电特性两个方面的研究试验,获得了显著提升椭圆软波导组件实际功率容量的方法,很好地解决了耐功率问题,具有一定的工程应用价值。     

Double heterojunction AlxGa1-xAs/GaAs bipolar transistors (DHBJT's) by MBE with a current gain of 1650

Double heterojunction AlGaAs/GaAs bipolar junction transistors (DHBJT's) grown by molecular beam epitaxy (MBE) were fabricated and tested. Devices with 0.2-µm and 0.1-µm base thicknesses exhibited common emitter current gains of up to 325 and 1650, respectively, in a wide range of collector currents. To obtain such high current gains, growth conditions had to be optimized and controlled. These high current gains, compared with the previous best value of 120 obtained in a MBE-grown transistor, make the HBJT's very promising for low-power high-speed logic application.     

Schottky diodes of Au on GaAs1-xSbx/GaAs n-Nheterostructures grown by MBE

Au Schottky barrier heights on molecular-beam-epitaxial grown n-GaAs_1-xSb_x/N-GaAs heterostructures with x up to 0.26 have been studied. It was found that φ_bn=0.9-1.77x+2.89x², or φ_bn≈0.77E_g-0.20 for x<0.26. The pinning position of the Fermi level with respect to the valence-band edge for x<0.26 takes the form of E _pin=-0.52x+0.53 eV, which also appears to be valid for an x value up to 1.0     

A numerical study of performance potential of Si1-xGex pseudomorphic heterojunction bipolar transistors

A two-dimensional drift-diffusion (DD) simulation and a one-dimensional hydrodynamic (HD) simulation are used to analyze the high-frequency performance of advanced Si BJTs and Si_1-xGe _x pseudomorphic HBTs (PHBTs). The results on similar experimental devices are compared, and good agreement is observed for the Si device. Based on this agreement, it is estimated that equivalent Si_1-xGe_x PHBTs should obtain an f_T of ≈70 GHz. DD results give a maximum f_T of 60 GHz, but HD results suggest the higher figure of 70 GHz. Details of device operation are examined and sources of improved performance identified. Improved HD model parameters, most importantly the mobility, are discussed