Double Heterostructure AlGaAs Research Articles

Near‐Unity External Quantum Efficiency in GaAs|AlGaAs Heterostructures Grown by Molecular Beam Epitaxy

The external quantum efficiency (EQE) of a GaAs|AlGaAs double heterostructure, grown by molecular beam epitaxy, is measured as a function of temperature in the range of 350–100 K. Record EQEs of >80% at 300 K and >98% below 150 K are obtained. The temperature‐dependent lifetime measurement that corroborates the EQE data is also reported, suggesting that interface recombination remains the dominant mechanism for nonradiative decay. These results offer promising prospects for using these structures in thermal photovoltaic, electroluminescent, and laser cooling device applications.

Glide of threading dislocations in (In)AlGaAs on Si induced by carrier recombination: Characteristics, mitigation, and filtering

III-V optoelectronics grown epitaxially on Si substrates have large networks of dislocations due to a lattice constant mismatch between the device layers and the substrate. Recombination-enhanced dislocation glide (REDG) allows these dislocations to move and increase in length during device operation, which degrades performance. In this paper, we study REDG dynamics of threading dislocations in situ in (In)AlGaAs double heterostructures grown on Si substrates using scanning electron microscopy cathodoluminescence. The driving force for REDG arises due to the coefficient of thermal expansion differences between Si and the III-V layers leading to large residual strains in the films. Tracking of threading dislocations as moving dark spot defects reveals glide characteristics that vary based on the nature of the dislocation. Remarkably, the alloying of a few atom percent of indium using metamorphic structures arrests threading dislocation glide by more than two orders of magnitude. Finally, we present REDG-based filtering as a pathway to reducing the threading dislocation density in select areas, removing a large fraction of the mobile dislocations. Together, these techniques will enable the understanding of dislocation–dislocation and carrier–dislocation interactions that have so far remained elusive during device operation, leading to reliable III-V integrated optoelectronics on silicon.

Effect of temperature on resistance of LEDs based on AlGaAs heterostructures to 60Co gamma radiation

The paper presents the results obtained in the study of the change in the parameters of IR LEDs based on AlGaAs double heterostructures under 60Co gamma irradiation with regard to irradiation temperature. The study indicated several consecutive stages of LED emissive power lowering under ionizing radiation. Increased temperature during gamma irradiation enhances radiation resistance at the first stage due to radiation-stimulated defect annealing, which reduces relative contribution of the first stage to the overall emissive power lowering. It was found that in exposure at temperature more than 380 K, the first stage of LED emissive power lowering is completely eliminated. At the second stage, increase in resistance is caused by the decreased relative contribution of the less stable first stage to the overall emissive power lowering. The maximum resistance of LEDs to gamma radiation depends on radiation resistance of metal–semiconductor contacts.

Influence of irradiation by 60Co gamma‐quanta on reliability of IR‐LEDs based upon AlGaAs heterostructures

AbstractWe consider the influence of preliminary irradiation by 60Co gamma quanta on emission power decrease during the operating time of IR‐LEDs based upon AlGaAs double heterostructures. Irradiation was realized in passive power mode of the LEDs prior to aging. Aging under long operating time conditions was simulated by a step‐stress approach. We have determined that the emissive power decrease of LED during operating time has two stages. On the first stage, decrease of LED emissive power is due to rearrangement of original defect structure. On the second stage, emissive power goes down as the result of inducing new structural defects. We have shown identical multistage mechanisms of emissive power drop are observed during both operating time and influence of ionizing radiation. We have established that preliminary irradiation has increased reliability and operating time of LEDs. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Preparation characterization of MnSb–GaAs spin LED

Spin light-emitting-diodes (spin-LEDs) composed of an epitaxial MnSb layer having in-plane magnetization and GaAs–AlGaAs double hetero-structures were prepared using a two-chamber MBE system. Electroluminescence extracted through the cleaved side walls showed elliptically polarized light emission with circular polarization of 2.1% at 30K without an auxiliary external magnetic field.

Performance of sub-atmospheric pressure hydride gas source and delivery system for MOCVD

A sub-atmospheric pressure gas enhanced (SAGE™) arsine source and delivery system has been evaluated and found to meet the flow rate and gas purity requirements of metal-organic chemical vapor deposition (MOCVD) processes. Gas delivery at 80 kPa and with flow rates up to 10 slpm have been accomplished using a specially developed extractor unit. AlGaAs double hetero structures grown with SAGE and high-pressure (HP) arsine sources have been characterized by secondary ion mass spectrometry (SIMS) to verify gas purity. SAGE arsine was found to be equivalent to the HP arsine reference, with regard to oxygen incorporation, provided the recommended SAGE delivery system startup procedures were adhered to. Cylinder depletion studies also showed that the moisture concentration in SAGE arsine slowly decreases over the cylinder lifetime, whereas in HP arsine, it rises as the last third of the cylinder is consumed. These findings, together with the enhanced safety features and potential for scale up, make SAGE technology particularly attractive for routine production of commercial devices.

Broad continuous frequency tuning of a diode laser with an external cavity

A broad continuous frequency tuning of a double-heterostructure AlGaAs GaAs diode laser with a short dispersive external cavity has been examined both theoretically and experimentally. The external cavity has been composed by a micro lens and a Littrow diffraction grating placed 10-mm apart from a non-perfectly AR-coated front facet of the laser chip. The frequency tuning has been accomplished by simultaneously varying the optical lengths of the internal and external laser cavities due to an opto-electrical feedback. Continuous frequency tuning over 200 GHz near 850-nm wavelength with a sweep rate of 111 000 GHz/s has been obtained.

Effects of electron beam irradiation on transient photoluminescence measurements of GaAs and AlGaAs double heterostructures

We have performed transient photoluminescence measurements on Se doped AlGaAs and GaAs double heterostructure materials (similar to those found in advanced solar cells) as a function of radiation fluence from 1 MeV electrons for total fluences between 1/spl times/10/sup 13/ and 1/spl times/10/sup 15/ e/sup -//cm/sup 2/. We extract the effective minority carrier lifetime from the transient photoluminescence measurements and use these results to obtain lifetime damage coefficients. Carrier lifetimes in the un-irradiated samples range from a few nsec for heavily doped samples to almost 100 nsec for the more lightly doped samples. Bombardment with energetic electrons causes the carrier lifetime to decrease to values in the range of 100-200 psec. Lifetime damage coefficients are obtained for Al concentrations of 0, 10, and 20% and for Se donor concentrations between 3/spl times/10/sup 16/ and 1.5/spl times/10/sup 18/ cm/sup -3/. To our knowledge, these are the first direct measurements of lifetime damage coefficients in GaAs and AlGaAs double heterostructures. The values extracted for lifetime damage coefficients suggest: (1) greater damage than the values obtained from previous measurements using indirect techniques; (2) that the AlGaAs samples are more susceptible to reduction of carrier lifetime than are the GaAs samples; and (3) that the damage depends upon dopant concentration. We discuss the implications of these measurements for solar cell degradation in the space radiation environment.

The growth and characterization of AlGaAs double heterostructures for the evaluation of reactor and source quality

AlGaAs double heterostructures are grown by low-pressure metalorganic chemical vapor deposition to evaluate the level of oxygen contamination in different trimethylaluminum sources. Effects of arsine purifiers, misoriented substrates, atmospheric exposure of the growth chamber, and possible phosphorus contamination are also studied. Extensive characterization is performed on these films by a variety of methods, including high-resolution x-ray diffraction, photoluminescence (PL), time-resolved photoluminescence, and secondary-ion mass spectrometry. The PL intensities for structures grown with the low-alkoxide grade are reproducibly much greater than those grown with the regular-grade TMA1. The use of AsH3 purification improves the PL intensity.

Theoretical study of the effect of an AlGaAs double heterostructure on metal-semiconductor-metal photodetector performance

The impulse and square-wave input response of different GaAs metal-semiconductor-metal photodetector (MSM) designs are theoretically examined using a two dimensional drift-diffusion numerical calculation with a thermionic-field emission boundary condition model for the heterojunctions. The rise time and the fall time of the output signal current are calculated for a simple GaAs, epitaxially grown, MSM device as well as for various double-heterostructure barrier devices. The double heterostructure devices consist of an AlGaAs layer sandwiched between the top GaAs active absorption layer and the bottom GaAs substrate. The effect of the depth of the AlGaAs layer on the speed and responsivity of the MSM devices is examined. It is found that there is an optimal depth, at fixed applied bias, of the AlGaAs layer within the structure that provides maximum responsivity at minimal compromise in speed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

AlGaInP / AlGaAs double heterostructure light emitting diode grown by liquid phase epitaxy

AlGaInP is the most promising material for visible wavelength light sources for laser-printing and audio compact disc systems. Unfortunately, it is difficult to grow controllably this crystal by conventional liquid phase epitaxy (LPE) growth, dur to the extremely large distribution coefficient of Al in the In melt. In this work, the AlGaInP layers have been grown in a very short time on an Al 0.9Ga 0.1As buffer layer from a non-equilibrium solution with a vey high Al fraction. The AlGaInP source melt was prepared by changing the Al mole fraction for a fixed value of Ga and P mole fractions which were for InGaP lattice-matched to GaAs. A mirror-loke surface has been obtained at an Al mole fraction X 1 Al between 1.96 × 10 -5 and 3.21 × 10 -4. Photoluminescence measurements indicated that the peak wavelength shifted to the shorter side and show that Al was incorporated into the crystals. The shortest peak wavelegth observed at room temperature was 635 nm from the AlGaInP layer grown at X 1 Al = 3.21 × 10 -4. AlGaAs /AlGaInP / AlGaAs double heterostructure (DH) light emitting diodes (LEDs) were fabricated by this growth method with X 1 Al = 1.82 × 10 -4. The electroluminescence (EL) emission peak at 645 nm with full width at half maximum of 66 meV was obtained at room temperature.

Ultra-high efficiency light-emitting-diode arrays

An approach to increasing the escape probability for light-emitting diodes (LEDs) is proposed which involves the angular randomization by elastic scattering of the photons from a textured semiconductor surface. The approach has two components: (i) separation of thin-film heterojunctions from the growth substrate using the epitaxial liftoff (ELO) technique, and (ii) nanotexturing of the thin-film semiconductor interface by natural lithography. The LED structure is a conventional n/sup +/-AlGaAs/p-GaAs/p/sup +/-AlGaAs double heterostructure, grown over a 0.05 mu m thick AlAs release layer by organometallic chemical vapor deposition. The light versus current characteristics of the LEDs have been measured and modeled. A 9% external quantum efficiency from the untextured LED array was observed, transforming into a 30% external quantum efficiency following the surface texturing treatment. It is concluded that, by employing the principle of phase-space-filling in an improved device geometry, 56% efficient LED arrays can be expected.

An overview of visible light emitting diode (LED) development and the potential for AlInGaP devices

Recent developments in light-emitting diode (LED) materials growth and device properties are considered. The brightness of LEDs has increased in recent years, permitting new applications. Double heterostructure AlGaAs red LEDs on transparent 'substrates' are now commercially available for outdoor displays and signaling applications. Recently, AlInGaP LEDs grown by metalorganic chemical vapor disposition (MOCVD) have exhibited record performance in the yellow and red-orange spectral regions. External quantum efficiencies of greater than 5% and luminous performance as high as 20 lm/W at 590 nm have been reported. This performance is higher than that of conventional incandescent bulbs.

Analysis of transient photoluminescence measurements on GaAs and AlGaAs double heterostructures

The analysis of transient photoluminescence measurements and extraction of carrier recombination lifetimes in GaAs and AlGaAs double heterostructures is discussed. In contrast to recently reported claims, it is demonstrated that even in regions where the measured decay curves show single exponential behavior, the slopes do not, in general, correspond to any single physical carrier lifetime such as the minority-carrier lifetime. A series of measurements over a range of incident optical intensities is required to extract such lifetimes.

MBE as a production technology for AlGaAs lasers

We are the first to succeed in the mass production of AlGaAs visible-wavelength semiconductor laser on a commercial basis using MBE. Single-transverse-mode self-aligned AlGaAs double heterostructure (DH) lasers were fabricated by a two-step molecular beam epitaxial technique. A GaAs layer was thermally etched selectively in the MBE system just prior to regrowth. There was no problem associated with the regrowth of an AlGaAs layer after the thin GaAs passivation layer was removed. This self-aligned structure by MBE affords high control of transverse and longitudinal modes, which results in high quality laser for various applications such as compact disc, video disc, laser beam printer and optical memory disc.

Detection of Persisting Photoelectrons in AlGaAs Double Heterostructure Laser Diodes by DLTS

LPE-made AlGaAs double heterostructure laser diodes were investigated by deep level transient spectroscopy. In the Sn-doped n-type confinement layers two electron traps named DX1 and DX2 here were always found. Under non-saturation conditions a significant change of the low-temperature part of DLTS spectra curves was observed after applying forward voltage for a short time. Relaxation of DLTS signal and sample capacitance at 80 K took several hours. Only the DX2 trap contributed to this persistent photoconductivity effect.

Hole and electron traps in AlGaAs single and double heterojunction red light-emitting diodes

ABSTRACT Single and double heterostructure AlGaAs red LEDs, p+–N and n+–P AlGaAs-GaAs heterodiodes have been fabricated by liquid phase epitaxy (LPE). The presence and characteristics of deep centres located near the injection-active boundaries has been studied. Capacitance-temperature, electroluminescence, photocurrent and deep-level transient spectroscopy (DLTS) measurement have been performed. In n+–P structures a new Zn-related deep hole majority trap, at about 0·3 eV above the valence band, was found. In all p+–N heterojunctions, in addition to a majority electron trap related to the Te-dopant (DX defects), some acceptor-like traps have been detected.

Investigation of mechanisms of multimode emission from double-heterostructure AlGaAs injection lasers with narrow stripe contacts

An investigation was made of the spectral characteristics of planar stripe (contact width 6--8 ..mu..) lasers made of AlGaAs heterostructures. The steady-state emission spectrum could be of multimode type because of the high level of spontaneous emission in the lasing mode. The spectrum then became narrower on increase in the power and in the limit changed to the single-mode form. However, in the presence of self-modulation processes the multimode nature of the emission spectrum could be explained by a theory of transient effects and in this case the width of the spectrum increased on increase in the power.

Wavelength-change characteristics of semiconductor lasers and their application to holographic contouring

The dependence of double-heterostructure AlGaAs semiconductor laser wavelength on injection current and temperature was investigated by means of a Michelson interferometer. The lasers operated in a single longitudinal mode at 790 nm, permitting them to be applied to two-wavelength holographic contouring. Continuous change and discontinuous change by mode hopping were observed. The wavelength was continuously tunable by variation of injection current and temperature at rates of 0.0045 nm/mA and 0.070 mm/ degrees C, respectively. Discontinuties in wavelength change were observed to be integer multiples of the longitudinal mode spacing. Holographic contour fringes were interpreted given the measured variation in wavelength.

Heterostructure semiconductor lasers prepared by molecular beam epitaxy

<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.72-0.88 \mu</tex> m (AlGa)As, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.3-1.65 \mu</tex> m GaInAsP and AlGa-InAs, and 1.78 μm AlGaSb double-heterostructure (DH) lasers were prepared by molecular beam epitaxy. For AlGaAs DH lasers very low 300 K threshold current densities and long operating life (mean time to failure >10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> h at 300 K) were achieved and optical transmitters containing MBE-grown lasers have been field-tested. For lasers with lasing wavelength <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;1\mu</tex> m, MBE is in the development stage. The unique capabilities of MBE as an epitaxial growth technique and its important contributions to the field of optoelectronics are illustrated by a discussion of a new class of laser structures including quantum well heterostructure of GaAs/ Al <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> Ga <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</inf> AS and Ga <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</inf> In <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</inf> As/InP, double-barrier double-heterostructure, and graded-index waveguide separate-confinement-heretostructure lasers. These new lasers, made possible by MBE, have characteristics unmatched by conventional liquid phase epitaxial growth techniques.