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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Red-emitting Ga/As,P///In,Ga/P heterojunction lasers

The paper describes in detail the properties of vapor-grown double-heterojunction lasers of Ga(As,P)/(In,Ga)P with room-temperature threshold current densities as low as 3400 A/sq cm at 7000 A and 6600 A/sq cm at 6800 A. These thresholds are three to eight times smaller than those of (Al,Ga)As lasers in this wavelength range due to the shorter-wavelength direct-indirect transition in Ga(As,P). The optical and electrical characteristics of the Ga(As,P)/(In,Ga)P lasers are found to be similar to those of (Al,Ga)As, with fundamental transverse-mode operation to 70 C, and spontaneous carrier lifetimes between 5 and 8 nsec typically observed at low current densities.

Kressel, H.↗
NASA NTRS1980

Germanium-on-InP heterojunction-structure LED

Ge-on-InP heterojunction structure LED has been developed where in Ge film is evaporated onto commercially available InP substrate. Forward bias of device is approximately 1 volt, and it emits light in 9.800 angstrom region. Technique permits easy and inexpensive fabrication of LED for application at this wavelength.

Hawrylo, F. Z.↗
NASA NTRS1979

A theoretical study of heterojunction and graded band gap type solar cells

The work performed concentrated on including multisun effects, high temperature effects, and electron irradiation effects into the computer analysis program for heterojunction and graded bandgap solar cells. These objectives were accomplished and the program is now available for such calculations.

Chiang, J. P. C.↗
NASA NTRS1979

Optimum bandgap of several III-V heterojunction solar cells

Results of computer analysis of AlAs/Ga(1-x)As n-on-p heterojunction solar cells are presented with particular consideration given to interface recombination effects. It is found that, for an AlAs window layer, GaAs appears to be the optimum semiconductor for the active layer. Furthermore, even if the interface recombination is neglected, GaAs comes so close to being the optimum III-V active layer material that the additional effort required to incorporate a few percent of InAs into the active layer appears to be much greater than any expected efficiency increase.

Sutherland, J. E.↗
NASA NTRS1979

Internal stress and degradation in short-wavelength AlGaAs double-heterojunction devices

Aging tests of incoherently operated zinc-doped double-heterojunction (DH) lasers designed for short-wavelength (0.71-0.72 micron) operation show that the introduction of buffer layers between the substrate and the DH structure leads to a drastic reduction in gradual degradation. This is attributed to a decrease in lattice mismatch stress.

Ladany, I.↗
NASA NTRS1980

New PbSnTe heterojunction laser diode structures with improved performance

Several recent advances in the state-of-the-art of lead tin telluride double heterojunction laser diodes are summarized. Continuous Wave operation to 120 K and pulsed operation to 166 K with single, lowest order transverse mode emission to in excess of four times threshold at 80 K were achieved in buried stripe lasers fabricated by liquid phase epitaxy in the lattice-matched system, lead-tin telluride-lead telluride selenide. At the same time, liquid phase epitaxy was used to produce PbSnTe distributed feedback lasers with much broader continuous single mode tuning ranges than are available from Fabry-Perot lasers. The physics and philosophy behind these advances is as important as the structures and performance of the specific devices embodying the advances, particularly since structures are continually being evolved and the performance continues to be improved.

Fonstad, C. G.↗
NASA NTRS1980

Theory of extrinsic and intrinsic heterojunctions in thermal equilibrium

A careful analysis of an abrupt heterojunction consisting of two distinct semiconductors either intrinsic or extrinsic is presented. The calculations apply to a one-dimensional, nondegenerate structure. Taking into account all appropriate boundary conditions, it is shown that the intrinsic Fermi level shows a discontinuity at the interface between the two materials which leads to a discontinuity of the valence band edge equal to the difference in the band gap energies of the two materials. The conduction band edge stays continuous however. This result is independent of possible charged interface states and in sharp contrast to the Anderson model. The reasons for this discrepancy are discussed.

Von Ross, O.↗
NASA NTRS1980

Low-threshold high-T/0/ constricted double heterojunction AlGaAs diode lasers

Constricted double heterojunction diode lasers of relatively low CW thresholds (28-40 mA) are obtained by growing structures that maximize the amount of current flow into the lasing spot. These values are obtained while still using standard 10 microns wide oxide-defined stripe contacts. Over the 20-70 C temperature interval, threshold current temperature coefficients as high as 320 C and a virtually constant external differential quantum efficiency, are found.

Botez, D.↗
NASA NTRS1981

High-temperature CW and pulsed operation in constricted double-heterojunction AlGaAs diode lasers

The behavior of constricted double-heterojunction (CDH) diode lasers has been investigated up to 170 C CW and 270 C pulsed. It is found that the temperature-dependent current concentration effect responsible for low threshold-current sensitivity and temperature-invariant external differential quantum efficiency in CDH lasers saturates at about 100 C. It is also found that over a wide temperature interval (180-280 C) the threshold current density has a To value of 40-50 C and that the spontaneous emission becomes increasingly sublinear above 220 C. Both effects are believed to reflect Auger recombination.

Botez, D.↗
NASA NTRS1981

Very low threshold-current temperature sensitivity in constricted double-heterojunction AlGaAs lasers

The temperature dependence of threshold currents in constricted double-heterojunction diode lasers with strong lateral mode confinement is found to be significantly milder than for other types of lasers. The threshold-current relative variations with ambient temperature are typically two to three times less than for other devices of CW-operation capability. Over the interval 10-70 C the threshold currents fit the empirical exponential law exp/(T2-T1)/T0/ with T0 values in the 240-375 C range in pulsed operation, and in the 200-310 C range in CW operation. The external differential quantum efficiency and the mode far-field pattern near threshold are virtually invariant with temperature. The possible causes of high-T0 behavior are analyzed, and a new phenomenon - temperature-dependent current focusing - is presented to explain the results.

Botez, D.↗
NASA NTRS1982

Studies of single-mode injection lasers and of quaternary materials. Volume 1: Single-mode constricted double-heterojunction AlGaAs diode lasers

Constricted double-heterojunction (CDH) lasers are presented as the class of single-mode nonplanar-substrate devices for which the lasing cavity is on the least resistive electrical path between the contact and the substrate. Various types of CDH structures are considered under three general topics: liquid-phase epitaxy over channeled substrates, lateral mode control, and current control in nonplanar-substrate devices. Ridge-guide CDH lasers have positive-index lateral-mode confinement and provide: single-mode CW operation to 7 mW/facet at room temperature and to 3 mW/facet at 150 C; light-current characteristics with second-harmonic distortion as low as -57 dB below the fundamental level; threshold-current temperature coefficients, as high as 375 C (pulsed) and 310 C (CW); constant external differential quantum efficiency to 100 C; and lasing operation to 170 C CW and 280 C pulsed. Semileakyguide CDH lasers have an asymmetric leaky cavity for lateral-mode confinement and provide single-mode operation to 15 to 20 mW/facet CW and to 50 mW/facet at 50% duty cycle. Modulation characteristics and preliminary reliability data are discussed.

Botez, D.↗
NASA NTRS1981

Constricted double-heterojunction AlGaAs diode lasers - Structures and electrooptical characteristics

Constricted double-heterojunction (CDH) diode lasers are presented as a class of nonplanar-substrate devices for which the lasing cavity is on the least resistive electrical path between the contact and the substrate. Various CDH structures are discussed while treating such topics as liquid-phase epitaxy over channeled substrates, lateral mode control, and current control in nonplanar-substrate devices. Ridge-guide CDH lasers with positive-index lateral mode confinement provides single-mode CW operation to 7 mW/facet at room temperature and to 3 mW/facet at 150 C, while exhibiting light-current characteristics with second-harmonic distortions as low as -57 dB below the fundamental level. Semileaky guide CDH lasers with an asymmetric leaky cavity provide single-mode operation to 15-20 mW/facet CW, and to 50 mW/facet at 50% duty cycle.

Botez, D.↗
NASA NTRS1983

Reliability of constricted double-heterojunction AlGaAs diode lasers

Constricted double-heterojunction diode lasers have been life tested at 70 C heatsink temperature and 3-4 mW/facet in CW operation. A median life of 7800 h is obtained at 70 C, which extrapolates to 400,000 h median life at room temperature. The extrapolated mean time to failure at room temperature is in excess of 1,000,000 h. Single-longitudinal-mode CW operation is maintained after 10,000 h of accelerated aging at 70 C.

Botez, D.↗
NASA NTRS1987

Microwave characterization and modeling of GaAs/AlGaAs heterojunction bipolar transistors

The characterization and modeling of a microwave GaAs/AlGaAs heterojunction Bipolar Transistor (HBT) are discussed. The de-embedded scattering parameters are used to derive a small signal lumped element equivalent circuit model using EEsof's Touchstone software package. Each element in the equivalent circuit model is shown to have its origin within the device. The model shows good agreement between the measured and modeled scattering parameters over a wide range of bias currents. Further, the MAG (maximum available power gain) and the h sub 21 (current gain) calculated from the measured data and those predicted by the model are also in good agreement. Consequently, the model should also be capable of predicting the f sub max and the f sub T of other HBTs.

Simons, Rainee N.↗
NASA NTRS1987

Self-consistent analysis of gain saturation in channeled-substrate-planar double-heterojunction lasers

A self-consistent model for semiconductor lasers (using the channeled-substrate-planar (CSP) double-heterojunction (DH) laser as an example) which does not assume constant optical power along the laser axis is developed. This approach allows for the analysis of high-power lasers with low facet reflectivities which produce nonuniform photon densities along the propagation direction. Analytical equations for the modal gain coefficient, the threshold current density, and the radiated power for a specific CSP laser structure are obtained.

Butler, Jerome K.↗
NASA NTRS1988

Deposition and characterization of ZnS/Si heterojunctions produced by vacuum evaporation

Isotype heterojunctions of ZnS (lattice constant 5.41 A) were grown on silicon (lattice constant 5.43 A) p-n junctions to form a minority-carrier mirror. The deposition process was vacuum evaporation from a ZnS powder source onto a heated (450 C) substrate. Both planar (100) and textured (111) surfaces were used. A reduction of the minority-carrier recombination at the surface was seen from increased short-wavelength quantum response and increased illuminated open-circuit voltage. The minority-carrier diffusion length was not degraded by the process.

Landis, Geoffrey A.↗
NASA NTRS1990

Wide-bandgap epitaxial heterojunction windows for silicon solar cells

It is shown that the efficiency of a solar cell can be improved if minority carriers are confined by use of a wide-bandgap heterojunction window. For silicon (lattice constant a = 5.43 A), nearly lattice-matched wide-bandgap materials are ZnS (a = 5.41 A) and GaP (a = 5.45 A). Isotype n-n heterojuntions of both ZnS/Si and GaP/Si were grown on silicon n-p homojunction solar cells. Successful deposition processes used were metalorganic chemical vapor deposition (MO-CVD) for GaP and ZnS, and vacuum evaporation of ZnS. Planar (100) and (111) and texture-etched - (111)-faceted - surfaces were used. A decrease in minority-carrier surface recombination compared to a bare surface was seen from increased short-wavelength spectral response, increased open-circuit voltage, and reduced dark saturation current, with no degradation of the minority carrier diffusion length.

Landis, Geoffrey A.↗
NASA NTRS1990

Ensemble Monte Carlo characterization of graded Al(x)Ga(1-x)As heterojunction barriers

The current-voltage characteristics of graded Al(x)Ga(1-x)As heterojunction barriers were investigated using a self-consistent ensemble Monte Carlo method. Results are presented for barriers with two doping levels (10 to the 15th/cu cm and 10 to the 17th/cu cm) and two barrier heights (100 and 265 meV). It was found that the lower barrier structure exhibited little rectification at room temperature at both doping levels, while the higher barrier exhibited considerable rectification. The structures with the lower doping value exhibited a smaller current in both forward and reverse regions, due to space-charge effect. The results of studies of the energy and momentum distribution functions along the barrier indicate that the assumption of drifted Maxwellian distribution used in energy-momentum models is not justified for Gamma valley electrons.

Kamoua, R.↗