Ron Kaspi
Air Force Research Laboratory
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Featured researches published by Ron Kaspi.
Journal of Applied Physics | 2003
Giovanni P. Donati; Ron Kaspi; Kevin J. Malloy
We present a rationalized biquadratic interpolation algorithm for calculating quaternary semiconductor parameters and apply it to determine the band gaps of AlGaInAs, AlGaInP, AlInAsSb, GaInPAs, and GaInAsSb over complete compositional ranges. Extension to include bicubic corrections and quinary alloys are discussed. The band gaps of lattice-matched AlGaInAsSb and AlGaInPAs are reported.
Applied Physics Letters | 2002
Ron Kaspi; Andrew P. Ongstad; G. C. Dente; Joseph Chavez; M. L. Tilton; Donald M. Gianardi
We report on optically pumped semiconductor lasers emitting near 3.8 μm that exhibit high power and low output divergence. The lasers incorporate multiple InAs/InGaSb/InAs type-II wells imbedded in an InGaAsSb waveguide that is designed to absorb the pump emission. When operated at 85 K, 0.25 mm×2.5 mm broad area devices produce >5 W of peak power under long pulse conditions. Moreover, these extremely bright devices exhibit a fast axis divergence of only ∼15° full width at half maximum (FWHM), coupled with a slow axis divergence of ∼6° FWHM. The first is due to the reduced optical confinement in the transverse direction, while the latter is attributed to the suppression of filament formation, which is another beneficial consequence of the low optical confinement.
Journal of Applied Physics | 2001
Andrew P. Ongstad; Ron Kaspi; Charles E. Moeller; Michael L. Tilton; Donald M. Gianardi; Joseph R. Chavez; Gregory C. Dente
We describe the photoluminescence spectroscopy (PL) and Fourier transform infrared absorbance spectroscopy characterization of a large set of InAs/GaSb type-II strained layer superlattice (SLS) samples. The samples are designed to probe the effect of GaSb layer thickness on the optical properties of the SLS, while the InAs-layer thickness is held fixed. As the GaSb layer thickness is increased, we observe a spectral blue shift of the PL peaks that is accompanied by an increase in intensity, narrower linewidths, and a large reduction in the temperature sensitivity of the luminescence. These effects occur despite a significant reduction in the electron-hole wave function overlap as the GaSb layer thickness is increased. In addition, we compare the results of empirical pseudopotential model (EPM) calculations to the observed blueshift of the primary band gap. The EPM calculations are found to be in very good agreement with the observed data.
Journal of Applied Physics | 2000
C. Mourad; Donald M. Gianardi; Kevin J. Malloy; Ron Kaspi
Stimulated emission at 1.994 μm was demonstrated from an optically pumped, double quantum well, semiconductor laser that was digitally grown by modulated-molecular beam epitaxy. This “digital growth” consists of short period superlattices of the ternary GaInAs/GaInSb and GaAsSb/GaSb/AlGaSb/GaSb alloys grown by molecular beam epitaxy with the intent of approximating the band gaps of quaternary GaInAsSb and AlGaAsSb alloys in the active region and barriers of the laser, respectively. For a 50 μs pulse and a 200 Hz repetition rate, the threshold current density was 104 W/cm2 at 82 K. The characteristic temperature (T0) was 104 K, the maximum operating temperature was 320 K and the peak output power was 1.895 W/facet at 82 K with pumping power of 7.83 W.
Applied Physics Letters | 2000
Ron Kaspi; Charles E. Moeller; Andrew P. Ongstad; Michael L. Tilton; Donald M. Gianardi; Gregory C. Dente; Prabhakara Gopaladasu
We describe the molecular-beam epitaxy growth, as well as both the structural and optical characterization of a set of InAs/GaSb type-II strained-layer superlattice samples, in which the GaSb layer thickness is systematically increased. Absorbance spectroscopy measurements show well-defined features associated with transitions from the various valence subbands to the lowest conduction subband, and also a significant blueshift of the band edge when the GaSb layers thickness is increased. Empirical pseudopotential method calculations are shown to successfully predict the blueshift and help identify the higher-energy transitions.
Applied Physics Letters | 2006
Ron Kaspi; Andrew P. Ongstad; G. C. Dente; J. R. Chavez; M. L. Tilton; Donald M. Gianardi
We provide an update on the further development of optically pumped semiconductor lasers based on the InAs∕InGaSb∕InAs type-II quantum wells. We show increased power generation, as well as the inherent flexibility to produce devices that can emit at any wavelength in the ∼2.4μm to ∼9.3μm range with consistently high photon-to-photon conversion rates.
Journal of Crystal Growth | 2001
Ron Kaspi; Jeremy David Steinshnider; M. Weimer; Charles E. Moeller; Andrew P. Ongstad
Abstract We have investigated the effect of a brief As 2 -soak at the GaSb surface on the nature of the InAs-on-GaSb interface. We find that As 2 efficiently removes Sb from GaSb and that a controlled As 2 -soak may be a necessary step in forming a “GaAs-like” interface without structural or optical degradation. We observe that the thickness of the “GaAs-like” interfacial layer and the band-edge transition wavelength in InAs/GaSb superlattices both increase with increasing As 2 -soak duration.
Journal of Crystal Growth | 2003
Ron Kaspi; Giovanni P. Donati
We consider the digital alloy growth of mixed As/Sb layers by molecular beam epitaxy. Using the (InAs)n(GaSb)3n superlattice as an example, we determine an acceptable upper limit to the modulation period before significant deviation from the In0.25Ga0.75As0.25Sb0.75 bandgap occurs. We then consider the digital alloy growth of In0.2Ga0.8AsySb1� y layers on GaSb, and find that the digital alloying technique provides protection against compositional drift in the growth direction due to reduced sensitivity to variations in arsenic-flux and substrate temperature. r 2002 Elsevier Science B.V. All rights reserved.
Journal of Applied Physics | 2002
Andrew P. Ongstad; Ron Kaspi; J. R. Chavez; Gregory C. Dente; Michael L. Tilton; Donald M. Gianardi
In this article, we report on a systematic study of mid-IR, W-Integrated Absorber (W-IA), lasers that employ strained InAs/InxGa1−xSb/InAs active layers, in which the indium content of the hole bearing InxGa1−xSb has been varied from xIn=0 to xIn=0.45. The output characteristics of the lasers improve as the In percentage is increased; the threshold temperature sensitivity (T0) values are observed to increase from ≈35 to ≈50 K. Further, the differential quantum efficiencies as a function of temperature are significantly improved in the devices with xIn⩾0.25. For samples with nominally eight monolayers (8 ML) InAs/7 ML InxGa1−xSb/8 ML InAs, the lasing wavelength at 84 K is observed to shift from 3.33 μm for xIn=0 out to a maximum of 4.62 μm for xIn=0.35. This large shift is well predicted by an empirical psuedopotential model; the model also predicts that the position of the hole wave function is sensitively dependent on strain level and that for xIn<0.25, the holes are no longer confined in the W active re...
Applied Physics Letters | 2001
Ron Kaspi; Andrew P. Ongstad; Charles E. Moeller; G. C. Dente; Joseph Chavez; M. L. Tilton; Donald M. Gianardi
We report optically pumped lasing at λ∼3.4 μm from an integrated absorber structure in which the electrons confined in the InAs quantum wells recombine with holes in adjacent InGaAsSb layers to provide the gain. This type-II laser exhibits an estimated photon-to-photon conversion rate of ∼24% at 85 K. The self-consistent empirical pseudopotential method calculations suggest that Coulomb attraction can lead to a strong enhancement in carrier overlap, and the resulting small shift in transition energy is consistent with that observed.