Efficient small-area GaAs-Ga1-xAlxAs heterostructure electroluminescent diodes coupled to optical fibers

A GaAs-Ga1-xAlxAs heterostructure prepared by liquid-phase epitaxy has been employed in the fabrication of efficient small-area (50-µm diameter) electroluminescent diodes, and the light output has been coupled into optical fibers. The light output through a short fiber was about 1 mW at a wavelength of 0.9 µm for a bias current of 200 mA dc. By comparison, the output from the most efficient diffused GaAs diodes of similar geometry was about 0.4 mW at this current.     

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.     

Modulation-doped MBE GaAs/n-AlxGa1-xAs MESFETs

Modulation-doped GaAs/n-Al0.3Ga0.7As MESFETs have been fabricated. At 77 K, DC transconductance of 160 mS mm^-1was observed, which is the highest transconductance value ever reported in this type of structure. The intrinsic transconductance was calculated to be 350 mSmm^-1, and the corresponding average electron drift velocity is 1.8 × 10⁷cm s^-1, which demonstrates the real advantage of this type of device in high-speed applications.     

Self-focusing effects in pulsating AlxGa1-xAs double-heterostructure lasers

Using proton bombarded stripe geometry lasers which emit intense optical pulses, we have measured the width of the optical beam in the plane of the junction as a function of time during the pulse. The width of the beam is qualitatively proportional to the change in the carrier density. The width increases during the quiescent period between pulses where the carrier density increases by current injection and decreases during the emission of the pulse. For one laser studied in considerable detail, the full width at half intensity decreases from 9 μm at the start of the pulse to 7.2 μm at the end of the pulse. The reduction in the width results from the self-focusing of the beam. It is due to an increase in the refractive index and the decrease in the gain distributions near the center of the stripe. The reduction in the beamwidth concentrates the mode to a region of sufficiently higher average gain to compensate for the reduction in spatial gain distribution. The self-focusing acts to reduce the damping of the relaxation oscillations, and thus enhances the effect of other nonlinearities such as saturable absorption in causing pulsations. The thermal induced refractive index distribution across the stripe is shown to play a crucial role in the gain instability caused by self-focusing.     

Dispersion of the refractive index of GaAs and AlxGa1-xAs

The real part of the complex refractive index near the fundamental absorption edge is calculated for the ternary compound AlxGa1-xAs,0 leq x leq 0.3, as a function of frequency. An analytical expression fornis given which is derived from a quantum mechanical calculation of the dielectric constant of a semiconductor assuming the band structure of the Kane theory. The expression obtained is a function of bandgap energy, effective electron and heavy hole masses, the spin orbit splitting energy, the lattice constant, and the carrier concentration for n-type or p-type materials. The refractive index at the absorption edge is found as a function of the material parameters above. This enables one to express theoretical results in terms of basic material parameters only, with no adjustable constants. Comparison of theory with available experimental data is given for various reported values of the bandgap energy and effective masses as functions of mole fractionx.     

Spectral broadening of pulsating AlxGa1-xAs double heterostructure lasers

The longitudinal mode spectrum of stripe geometry double heterostructure (DH) lasers exhibits a spectral broadening of ∼ 0.8 Å when the laser emits pulsations. The broadening results from a chirp to longer wavelengths which occurs during the ∼ 0.4 ns long pulse. The chirp is due to an increase of the refractive index resulting from the reduction in the carrier concentration during the pulse. Both plasma and band to band interactions affect the index change with the latter mechanism giving the dominant contribution. A comparison of the wavelength shift obtained during the pulse with the current dependent shift of the longitudinal modes at currents well below threshold confirms that the change in carrier concentration is responsible for the chirp.     

GaAs-AlxGa1-xAs integrated twin-guide lasers with distributed Bragg reflectors

A GaAs-AlxGa1-xAs integrated twin-guide (ITG) laser with distributed Bragg reflectors (DBR) was fabricated. The DBR was in the form of a third-order grating which was chemically etched on the surface of the output waveguide. The ITG lasers with distributed Bragg reflectors (DBR-ITG lasers) operating at room temperature showed single mode oscillation up to 1.5 times the threshold current and the half-side external quantum efficiency was 1 ∼ 2 percent.     

Fast switching and storage in GaAs—AlxGa1-xAs heterojunction layers

We experimentally show the possibility of fast switching and storage in GaAs-AlxGa1-xAs heterojunction layers in accordance with previous theoretical predictions. The switching of electrons between layers is shown to occur (at least) on a nanosecond scale. The storage times which can be accomplished are of the order of minutes at 77K and much longer at lower temperatures. These times make the effect an attractive candidate for low temperature high-speed logic applications. It is speculated that for high Al mole fractionx, storage effects can even be achieved at room temperature.     

Electrooptic polarization modulation in multielectrode AlxGa1-xAs rib waveguides

A single mode rib waveguide (RWG) polarization modulator is described with a measured extinction ratio ≳27 dB, a power conversion ≈0.99, and a switching voltage of 12.5 V atlambda = 1.064 mum. The modulator is based on a modified stepDeltabeta-reversal configuration. Contact with CdO and an Au overlay ensures low optical losses (lsim1cm^-1) for both polarizations.     

High-field transport in organometallic VPE AlxGa1-xAs transferred-electron devices

The velocity-field characteristics of hot electrons in planar organometallic vapor phase epitaxial (VPE) AlxGa1-xAs (0.1 ≤ x ≤ 0.6) transferred-electron devices have been measured by the probe technique. The characteristics in layers with x ≤ 0.30 show normal subthreshold behavior. For x > 0.30, the characteristics exhibit high values of drift velocity. The effects are more enhanced when an undoped 0.4-µm GaAs buffer layer is grown first on the GaAs: Cr substrate before the ternary layer is grown. Monotonically increasing drift velocities with electric field, with a value of 2 × 10⁷cm/s at 6 kV/cm, have been measured in these devices. These effects and overshoots in the pulsed current-time profiles indicate the onset of real-space electron transfer at the heterointerface at high fields.     

Visible-light laser oscillation in indirect-bandgap AlxGa1-xAs (77 K)

Laser oscillation was accomplished at 77 K for the first time in indirect-gap AlxGa1-xAs (x = 0.46) incorporated with nitrogen atoms by ion implantation. Pumping was made by a coumarin 102 dye laser (480 nm). Threshold pumping power was6 times 10^{4}W/cm²in nitrogen-doped AlxGa1-xAs (x = 0.46), and laser oscillation was not observed in undoped samples. Nitrogen atoms, introduced into the undoped AlxGa1-xAs active layer, were found to work as isoelectronic traps and to be responsible for stimulated emission and laser oscillation.     

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.     

Transverse mode stabilized AlxGa1-xAs injection lasers with channeled-substrate-planar structure

A built-in passive waveguide mechanism is introduced in AlxGa1-xAs injection lasers by growing planar double heterostructure (DH) layers on a grooved GaAs substrate. The lasing mode is confined to the channel region due to excess absorption loss outside the channel. Stable fundamental mode oscillation is achieved up to twice the threshold current for a channel width of5-8 mu. Undesirable lasing behavior usually induced by transverse mode instability, such as nonlinear kinks in the light output versus current characteristics, are significantly reduced in the present lasers. The dc threshold current is 40-90 mA at room temperature. Median lifetime of 780 hours has been obtained during preliminary aging tests at a heat sink temperature of 70°C.     

Low threshold operation of 1.5-µm DFB laser diodes

Highly reliable distributed feedback (DFB) laser diodes operating at 1.5-μm wavelength range are fabricated through optimizing the device parameters. Thickness control of the active layer is found to be an essential factor in achieving low threshold operation of DFB lasers. The threshold current as low as 11 mA and stable single longitudinal mode CW operation up to 106°C is achieved with these DFB lasers.     

InxAl1-xAs/InP heterojunction insulated gate field effect transistors (HIGFET's)

Stability problems in conventional InP metal-insulator-semiconductor field effect transistors (MISFET's) have been overcome in InP heterojunction insulated gate FET's (HIGFET's) by replacing the insulator with InxAl1-xAs. We report on the fabrication and low-frequency operation of the HIGFET with a composition of x = 0.43. Transistor characteristics have been successfully modeled by an analytical MISFET model which indicate a low interfacial state density (≅ 10¹¹/cm²) and near flat-band condition.     

Heterojunction III—V alloy photodetectors for high-sensitivity 1.06-µm optical receivers

A new type of 1.06-µm solid-state detector is discussed, the inverted hetrojunction III-V alloy mesa photodiode, which offers quantum efficiencies near 1.00 percent, extremely low capacitance and transit time, and low dark currents. The characterstics of these detectors allow their use in sensitive 1.06-µm optical receivers which promise better signal-to-noise ratios in a number of applications than any other available 1.06-µm photodetector. In particular, an optimization procedure for selecting photodiode and preamplifier parameters to give the best signal-to-noise ratio under signal conditions is discussed and this technique is applied to a proposed system application. It is shown that in this laser-illuminated airborne night imaging system, a small area heterojunction III-V alloy photodiode detector in an optimized receiver should be able to give signal-to-noise ratios much higher than any other 1.06-µm detector approach, even though the other 1.06-µm detectors may have lower noise equivalent power (NEP) values than this receiver. This is an illustration of the fact that such "magic numbers" for detector comparision as NEP are applicable only to comparing similar types of detectors in certain specific types of applications (such as comparing IR photoconductors in a high background application), and are of very little value in determining the relative performance of different types of detectors for a given system application (such as comparing photomultipliers, avalanche photodiodes, and low-noise photodiodes for this application).     

Determination of carrier saturation velocity in high-performance InyGa1-yAs/AlxGa1-xAs modulation-doped field-effect transistors (0 ≤ y ≤ 0.2)

We describe a new method for determining the carrier saturation velocity υsatin modulation-doped field-effect transistors (MODFET's). High-performance pseudomorphic InyGA1-yAs/AlGaAs MODFET's (0 ≤ y ≤ 0.20) grown by MBE were tested, and the dependence of υsaton InAs mole fraction y was obtained. It was found that each device with y > 0 had a higher υsatthan a conventional GaAs/ AIGaAs MODFET (y = 0). Further, we believe that there is an optimum InAs mole fraction such that υsatis maximized. A pseudomorphic MODFET structure optimizing υsatmay also optimize overall device performance.