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  • 1
    Electronic Resource
    Electronic Resource
    Photoluminescence and intersubband absorption spectroscopy of interdiffused Si/SiGe quantum wells (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 1414-1421 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The interdiffusion and thermal stability of narrow Si/SiGe multi-quantum wells is investigated by photoluminescence and intersubband spectroscopy. The photoluminescence exhibits a blueshift as a function of the temperature of annealing. The activation energy of the intermixing process and the interdiffusion coefficient are deduced from the photoluminescence shift versus temperature of the anneal. The intersubband absorption is measured by photoinduced infrared spectroscopy on the interdiffused samples for light polarized perpendicular (z polarization) or parallel (x polarization) to the layer plane. In z polarization, the absorption of annealed samples exhibits a redshift respective to the as-grown sample which is enhanced as more levels are confined in the well. The magnitude of this shift is in good agreement with simulations based on the data obtained by photoluminescence experiments. The redshift of the intersubband absorption in x polarization is lower than in z polarization due to the lower dependence of the spin-orbit level on the quantum well profile. Bound-to-continuum absorption is broadened in interdiffused quantum wells. This enhancement is explained by the local variation of the effective mass along the growth axis of the interdiffused well. At high temperature of annealing and beyond the onset of relaxation, we still observe intersubband absorption with a ratio between z and x polarization measured by photoinduced spectroscopy which is slightly decreased. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362939
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  • 2
    Electronic Resource
    Electronic Resource
    Photoluminescence study of band-gap alignment of intermixed InAsP/InGaAsP superlattices (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 1944-1947 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The band-gap alignment of InAs1−xPx/In0.53Ga0.47As1−yPy strained heterostructures fabricated by selective As–P interdiffusion in an as-grown InP/In0.53Ga0.47As superlattice has been investigated using low-temperature photoluminescence. Interdiffusion is performed using thermal anneals with phosphorous gas ambient. By analyzing both the energy and the integrated intensity of the superlattice photoluminescence along with their dependences on excitation intensity, it is demonstrated that the superlattice band alignment is of type I for x(approximately-greater-than)0.58 and y〈0.21, whereas it switches to type II for x〈0.58 and y(approximately-greater-than)0.21. Simulations show that in contrast to the type-I situation the band discontinuity mainly occurs in the conduction band for the type-II superlattice. The transition from type-I to type-II band alignment is attributed to composition changes and strain development at the heterointerfaces. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360233
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  • 3
    Electronic Resource
    Electronic Resource
    Electroluminescence spectroscopy of AlGaAs/InGaAs and AlGaAs/GaAs high-electron-mobility transistors (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 2184-2189 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electroluminescence of pseudomorphic InGaAs high-electron-mobility transistors (HEMTs) on GaAs and of standard AlGaAs/GaAs HEMTs with ultrashort gate lengths is investigated at room and cryogenic temperatures. The spectral distribution of the emitted radiation is analyzed in the 0.7–1.6 eV energy range. In the case of pseudomorphic transistors, three different recombination lines originating from distinct layers are observed: a broad luminescence band around 0.8–0.9 eV; a doublet arising from confined subbands in the InGaAs layer; and a single peak coming from the GaAs substrate. The energy position and the temperature dependence of these different lines under various biases give valuable information on the physical mechanisms which occur under high-electric-field nonstationary transport: lattice self-heating (≈150 K at high-bias conditions), origin of the impact ionization in the channel of the quantum-well layer, and perpendicular transfer of hot holes which recombine with the barrier DX centers thus leading to the broad luminescence band. These characteristics are supported by comparison with analog standard HEMTs and with electrical measurements. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358797
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  • 4
    Electronic Resource
    Electronic Resource
    Simulation of optically pumped mid-infrared intersubband semiconductor laser structures (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 1970-1978 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A theoretical self-consistent investigation of optically pumped mid-infrared intersubband semiconductor laser with hot electron effects is presented. Electron dynamics under optical pumping are investigated within a rate equation formulation where particle and energy flow equations are derived from Boltzmann's equation using Fermi statistics. Electron-polar optical phonon interactions with suitable screening are calculated by using a macroscopic model with slab and interface phonon modes. Our calculations show that despite hot electron effects, population inversion between the first and second excited states can occur at low temperatures under intersubband optical excitation. It is anticipated that lasing in the mid-infrared can be achieved with asymmetric quantum well structures optimized for electron concentrations exceeding 1011/cm2. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363088
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  • 5
    Electronic Resource
    Electronic Resource
    Low temperature electroluminescence spectroscopy of high electron mobility transistors on InP (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 464-469 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electroluminescence spectroscopy of short gate high-electron-mobility transistors (HEMTs) on InP substrates is performed at cryogenic temperatures. Electroluminescence is a reliable tool to investigate impact ionization as compared to studies based on gate current which depend on the weakness of the intrinsic gate current intensity. In on-state biased devices, a low energy (0.7–0.9 eV) recombination band is observed which is related to radiative recombination of carriers created by impact ionization in the low band gap InGaAs channel. The evolution of the luminescence intensity versus bias applied to the device shows that the electroluminescence intensity and impact ionization depend on two competing parameters: the electric field in the gate–drain access area and the drain current intensity. We show that the so-called "kink'' effect, which is a noticeable increase of the output conductance and which is observed at relatively moderate drain bias (600–750 mV) in our devices, is not correlated with impact ionization. The electroluminescence of the device in the off state is also investigated. This study allows the direct observation of impact ionization in the off-biased channel of InP-based HEMTs. In this low current regime, the electroluminescence intensity follows the electric field, i.e., the drain–gate voltage until breakdown of the device occurs. The voltage breakdown of the device in the off state is discussed in terms of impact ionization in the InGaAs channel due to hot carriers originating from the gate leakage current. Finally, a method for reducing or avoiding impact ionization in these devices, i.e., for increasing the device reliability, is discussed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362749
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  • 6
    Electronic Resource
    Electronic Resource
    Selective band-gap blueshifting of InGaAsP/InGaAs(P) quantum wells by thermal intermixing with phosphorus pressure and dielectric capping (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 3607-3610 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Group V interdiffusion of strained and unstrained InGaAsP/InGaAs(P) quantum wells induced by thermal anneals at 650 °C with phosphorus gas pressure using photoluminescence spectroscopy and x-ray diffraction measurements have been investigated. The blueshift of the annealed quantum well photoluminescence peak exhibits large variations with the phosphorus pressure, with a minimum around 0.1 atm. Samples capped with a SiO2 layer only exhibit minor blueshifts, thus demonstrating the possibility of spatially selective control of the intermixing. A differential blueshift as large as 80 meV is presently obtained between capped and uncapped areas. The interdiffusion of the quantum well interfaces is shown to be dependent on the layer strain.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356072
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  • 7
    Electronic Resource
    Electronic Resource
    Detailed analysis of second-harmonic generation near 10.6 μm in GaAs/AlGaAs asymmetric quantum wells (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 215-217 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the observation of resonant intersubband second-harmonic generation in asymmetric GaAs/AlGaAs quantum wells using a cw or Q-switched tunable CO2 laser as the pumping source. The dependence of the second-harmonic intensity with the pump photon wavelength is presented for the first time. A Lorentzian-like second-harmonic line shape is found with a maximum at 10.9 μm and a linewidth of 0.4 μm (4.1 meV). These results are in good agreement with theoretical predictions. The expected quadratic dependence of the second-harmonic conversion efficiency with pump intensity is well verified for intensities up to 150 kW/cm2. The calibrated second-harmonic power reaches 0.13 μW for a cw pump power of 0.8 W. The value of 7.2×10−7 m/V deduced for the second-order nonlinear susceptibility is about 1900 times greater than that found in bulk GaAs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.103742
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  • 8
    Electronic Resource
    Electronic Resource
    Long-wavelength ((approximate)15.5 μm) unipolar semiconductor laser in GaAs quantum wells (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 3619-3621 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A unipolar semiconductor laser emitting in the mid-infrared spectral region is demonstrated. The laser scheme relies on a simple three-level system in GaAs/AlGaAs asymmetric coupled quantum wells. Population inversion between excited states is achieved by optical pumping of electrons from the ground state with a CO2 laser. Long-wavelength ((approximate)15.5 μm) laser emission is demonstrated. The laser is operated in the pulsed regime up to a temperature of 110 K and with an output peak power (approximate)0.4 W at 77 K. Unipolar quantum well semiconductor lasers based on this principle are capable of covering the long wavelength mid-infrared spectral region above 12 μm. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.120459
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  • 9
    Electronic Resource
    Electronic Resource
    Thermally induced charged carrier transfer and intersubband transitions in an asymmetrical coupled quantum well structure (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 197-199 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have observed thermally induced charged carrier transfer in an asymmetrical coupled quantum wells structure with energy separation between the first two subbands of the order of the LO phonon energy. In this structure, the population of the second subband is not negligible and intersubband transitions from the second to higher excited subbands can be measured. Due to charged carrier transfer, the built-in dc space charge electric field is changed, giving rise to a blueshift with increasing temperature of the ground to the first excited state intersubband transition. Also, we have found that the measurements of thermally induced intersubband transitions from the second subband provide a direct way to estimate the energy separation between the second subband and the Fermi energy. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117370
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  • 10
    Electronic Resource
    Electronic Resource
    Optical saturation of intersubband absorption in GaAs-AlxGa1−xAs quantum wells (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 116-118 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated intersubband absorptions between the conduction ground state and the first excited state of two AlxGa1−xAs/GaAs/AlxGa1−xAs multiple quantum well structures with x=0.3 and 85 A(ring) well width, and with x=0.57 and 96 A(ring) well width. Small-signal measurements show absorption peaks at 10.45 and 10.15 μm, respectively. Under an intense resonant excitation from a pulsed CO2 laser, saturation of the intersubband absorption occurred. The saturation intensity is estimated to be 340±120 kW/cm2 for the first sample and 375±120 kW/cm2 for the second. From these values, we have deduced subband decay times of the order of 10.6±3.5 ps for the first sample and 15.5±5 ps for the second.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.100386
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