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  • 1
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Annual and seasonal variations in the low-latitude topside ionosphere are investigated using observations made by the Hinotori satellite and the Sheffield University Plasmasphere Ionosphere Model (SUPIM). The observed electron densities at 600 km altitude show a strong annual anomaly at all longitudes. The average electron densities of conjugate latitudes within the latitude range ±25° are higher at the December solstice than at the June solstice by about 100% during daytime and 30% during night-time. Model calculations show that the annual variations in the neutral gas densities play important roles. The model values obtained from calculations with inputs for the neutral densities obtained from MSIS86 reproduce the general behaviour of the observed annual anomaly. However, the differences in the modelled electron densities at the two solstices are only about 30% of that seen in the observed values. The model calculations suggest that while the differences between the solstice values of neutral wind, resulting from the coupling of the neutral gas and plasma, may also make a significant contribution to the daytime annual anomaly, the E × B drift velocity may slightly weaken the annual anomaly during daytime and strengthen the anomaly during the post-sunset period. It is suggested that energy sources, other than those arising from the 6% difference in the solar EUV fluxes at the two solstices due to the change in the Sun-Earth distance, may contribute to the annual anomaly. Observations show strong seasonal variations at the solstices, with the electron density at 600 km altitude being higher in the summer hemisphere than in the winter hemisphere, contrary to the behaviour in NmF2. Model calculations confirm that the seasonal behaviour results from effects caused by transequatorial component of the neutral wind in the direction summer hemisphere to winter hemisphere.
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 6908-6910 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the study of unstrained Ga0.64In0.36As0.84Sb0.16/InP multiple-quantum-well structures by room-temperature absorption spectroscopy. In the absorption spectra, strong and well-resolved exciton peaks were observed. By comparing these transition energies with a theoretical calculation, we estimated the valence-band offset ratio to be 0.7±0.05 for the Ga0.64In0.36As0.84Sb0.16/InP heterojunction. © 1999 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 3495-3497 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Unstrained Al0.66In0.34As0.85Sb0.15/In0.53Ga0.47As multiple-quantum-well (MQW) structures have been grown by metalorganic vapor phase epitaxy. Low-temperature photoluminescence was performed for these MQW structures. We compared the experimental data with the theoretical calculations. The conduction-band offset ratio of AlInAsSb/InGaAs heterojunction was set as an adjustable parameter in the theoretical model. We estimated the conduction-band offset ratio to be 0.90±0.05 for the Al0.66In0.34As0.85Sb0.15/In0.53Ga0.47As heterojunction. © 1999 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 2340-2342 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this study, a very thin Ni/Au bilayer metal film was prepared by electron beam evaporation and thermal alloying to form ohmic contact on p-type GaN film. After thermal alloying, the current–voltage (I–V) characteristic of Ni/Au contact on p-type GaN film exhibited ohmic behavior. The Ni/Au contacts showed a specific contact resistance of 1.7×10−2 Ω cm2 at an alloying temperature of 450 °C. In addition, the light transmittance of the Ni/Au (2 nm/6 nm) bilayer on p-type GaN was measured to be around 85% at 470 nm. These results suggest that a suitable metallization technology for the fabrication of light emitting devices can be achieved. © 1999 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 6017-6022 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This study investigated the thermally induced interdiffusion in ZnCdSe/ZnSe quantum wells and the outdiffusion of Ga atoms from the GaAs substrate by photoluminescence (PL), secondary ion mass spectrometry (SIMS), and contactless electroreflectance (CER) spectroscopy. The quantum well structures grown by molecular beam epitaxy were thermally annealed at temperatures between 250 and 700 °C. According to our results, the 15 K PL main peak disappeared when the annealing temperature reached 550 °C and above for samples grown with a 0.1 μm ZnSe buffer (sample A). In contrast, the PL main peak disappeared when the annealing temperature reached 600 °C and above for samples grown with 0.85 μm ZnSe buffer (sample C). In addition, for sample A, two extra PL peaks around 2.0 and 2.3 eV were observed when the annealing temperature reached 500 °C and above; those peaks were observed only when the annealing temperature reached 700 °C for sample C. SIMS results indicated the interdiffusion of Cd in the ZnCdSe/ZnSe quantum well regions in both samples. However, only sample A revealed a strong outdiffusion of Ga atoms from the substrate into the epilayer side, but a weaker one in sample C. The main peaks in PL spectra and the intersubband transitions in CER spectra disappeared owing to the Cd interdiffusion in the wells and the defect-related transitions introduced by the Ga outdiffusion onto the epilayer side. Based on the SIMS, PL, and CER spectra results, a thicker ZnSe buffer layer can increase the thermal stability of ZnCdSe/ZnSe quantum wells grown on GaAs substrates because of its effectiveness in mitigating the outdiffusion of Ga atoms into buffer layers and the interdiffusion of quantum well regions. © 1998 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 3172-3175 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this study, the Ni/Au layers prepared by electron beam evaporation and thermal alloying were used to form Ohmic contacts on p-type GaN films. Before thermal alloying, the current–voltage (I–V) characteristic of Ni/Au contact on p-type GaN film shows non-Ohmic behavior. As the alloying temperature increases to 700 °C, the I–V curve shows a characteristic of Ohmic contact. The Schottky barrier height reduction may be attributed to the presence of Ga–Ni and Ga–Au compounds, such as Ga4Ni3, Ga3Ni2, GaAu, and GaAu2, at the metal-semiconductor interface. The diffusing behavior of both Ni and Au have been studied by using Auger electron spectroscopy and Rutherford backscattering spectrometry. In addition, x-ray diffraction measurements indicate that the Ni3N and Ga4Ni3 compounds were formed at the metal-semiconductor interface. © 1998 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 1664-1669 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A study of near-band-edge optical properties of ZnSe epilayers grown on GaAs substrates using various modulation techniques is presented. We compare the contactless electroreflectance (CER) and piezoreflectance spectra to ascertain that our ZnSe epilayers of 1.2 μm in thickness grown on GaAs substrates are under a biaxial tensile strain. The defect-related transitions near the ZnSe/GaAs interface are also compared by identifying the photoreflectance and other spectra. In addition, in order to observe the temperature-dependent energy splitting and strains, we present a detailed investigation of the heavy-hole and light-hole related transition energies as a function of temperature in the 15–200 K range by identifying the excitonic signatures in the CER spectra. We have also calculated the energy splitting between heavy-hole and light-hole valence bands by utilizing the temperature-dependent elastic constants for ZnSe and the thermal expansion coefficients for ZnSe and GaAs. Both the experimental result and the theoretical calculation have shown a similar trend that the biaxial tensile strains decrease in magnitude with increasing temperatures in the 1.2 μm ZnSe epilayer grown on a GaAs substrate. © 1998 American Institute of Physics.
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  • 8
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The photoreflectance spectroscopy of the InxGa1−xAs/GaAs single-quantum well system has been measured at several reverse dc bias voltages. The spectrum can be divided into two parts by the photon energy; one belongs to the GaAs bulk transition and the other belongs to the InxGa1−xAs/GaAs quantum well transition. The GaAs transition has shown the Franz–Keldysh oscillations which can be used to deduce the strength of the electric field in the bulk GaAs. On the other hand, the InxGa1−xAs/GaAs quantum well transition has exhibited the quantum confined Stark effect; that is, the transition energy in the quantum well will be redshifted in the presence of an electric field. The field in the quantum well can be estimated from the amount of redshifting and it was found that the built-in field in the quantum well needs to be close to that of GaAs. © 1995 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 1970-1974 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This work investigates inductively coupled plasma (ICP) etching processes of GaN. Etching behaviors are also characterized by varying the ICP power, Cl2/Ar or Cl2/N2 mixing ratio, radio-frequency (rf) power, and chamber pressure. Experimental results indicate that the etching profiles are highly anisotropic over the range of etching conditions. Maximum etching rates of 8200 Å/min in Cl2/Ar plasma and 8330 Å/min in Cl2/N2 plasma are obtained as well. In addition, pressure, ICP power, Cl2/Ar(N2) flow ratio and rf power significantly influence etching rate and surface morphology. In particular, dc bias heavily influences the etching rates, suggesting that the ion-bombardment effect is an important factor of these etching processes. © 1999 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 8485-8489 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We performed the 1/f noise measurements on n-channel indium antimonide (InSb) metal–oxide–semiconductor field-effect transistors (MOSFETs) biased in linear and saturation regions operated at 77 K. Through the investigation of the dependence of drain voltage noise power spectral density on gate and drain bias, we have estimated the oxide–semiconductor interface trap density as a function of energy. In this analysis, both the noise magnitude and the spectral shape were studied. In this study, the frequency span was performed from 150 Hz to 5 kHz. The noise behavior of the device was modeled using the modified McWhorter Model, originally developed for silicon FETs. The interface trap concentration values computed from the low-frequency noise measurements using the previous model were found to agree closely with InSb/SiO2 interface properties measured by capacitance and conductance methods. © 1999 American Institute of Physics.
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