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  • 1
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of built-in biaxial strain on Γ-X transport in n-GaAs/i-InxAl1−xAs/n-GaAs pseudomorphic single-barrier structures (x=0, 0.03, and 0.06) are studied by measuring temperature-dependent I-V characteristics. For the accurate characterization of electron transport across each barrier, a self-consistent numerical model is used to analyze the experimental results. For each structure, the four barrier parameters defined from the thermionic-field-emission theory, the effective Richardson constant A*, the conduction-band offsets ΔEc1,2, and a tunneling mass mn* are extracted by calculating the theoretical I-V characteristics and fitting them to the experimental I-V-T data. The experimentally obtained X-point conduction-band shifts with the addition of indium are compared with the theoretical results calculated based on the model-solid theory. The results indicate that the addition of indium not only splits the degenerate X minima of the InxAl1−xAs barrier, but also shifts the relative barrier heights of both longitudinal and transverse X valleys due to the alloy-dependent band-structure modification. The comparison between the experimental and theoretical results illustrates that the transverse X valleys are the main conduction channel for the Γ-X transport across InxAl1−xAs pseudomorphic barriers. © 1994 American Institute of Physics.
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 6549-6556 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of biaxial strain on the intervalence-band absorption spectra of p-doped InGaAs/InP bulk layers are investigated. The study is performed by calculating and comparing the absorption coefficients corresponding to the direct transitions between the heavy and light hole bands, between the heavy hole and split-off bands, and between the split-off and light hole bands in both the lattice matched and the strained layers. The valence-band structures of these layers are neither isotropic nor parabolic and hence the k⋅p approach is utilized to calculate the band structures and their corresponding wave functions. The quantities are then invoked in the calculation of the (joint) density of states, the Fermi energy, and the momentum matrix element, which are needed in the evaluation of the intervalence-band absorption coefficients. These calculated results show that the intervalence-band absorption coefficients depend on the strain in the layer. The dependence is determined by the bands involved in the intervalence transition, the polarization of the incident light, and the type of the strain (compressive or tensile). © 1995 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 591-593 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An improved boundary condition treatment for the time-dependent Schrödinger equation applied to resonant-tunneling diode simulation has been developed. This treatment is half-implicit, or centered in time, and allows larger time steps than the previous explicit treatment. The method does not complicate the time-dependent calculation since the resulting matrix is still tridiagonal.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3564-3569 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Numerical solution of the time-dependent Schrödinger equation for resonant-tunneling diodes has been impeded by the difficulty in handling open-system boundary conditions. This paper presents a boundary condition method to simulate the interaction with ideal particle reservoirs at the device boundaries. A switching transient is calculated where the device is switched from the peak current state to the valley current state. In addition, this method was used to develop a small-signal analysis of resonant-tunneling diodes. Results for the small-signal equivalent circuit of a particular device versus frequency are presented.
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  • 5
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the dependence of the performance characteristics of In0.52 Al0.48As/ In0.53 Ga0.47 As resonant tunneling diodes upon molecular-beam-epitaxial growth parameters. The roughness of the growth front, leading to intrawell-size fluctuations and the V/III flux ratio at a fixed growth temperature are found to be important parameters affecting the performance of these devices. By means of a simple model, we have semiquantitatively related the peak current to the interface roughness. Defects and traps in the In0.52 Al0.48 As barriers, on the other hand, produced partially by nonoptimal V/III flux ratios, may produce shunt paths for tunneling, again reducing the resonant tunneling current peak-to-valley ratio. Under optimum growth conditions we have measured current peak-to-valley ratios of 6.1 and 21.6 at 300 and 77 K, respectively. These are the best values reported so far for this heterostructure system.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 867-869 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using a thin graded layer of InGaAs starting on GaAs and becoming InAs on the top, low-resistance alloyed and nonalloyed ohmic contacts have been achieved on n+-GaAs epilayers grown by molecular-beam epitaxy on a semi-insulating GaAs substrate. In addition, by a suitable choice of the multilayer ohmic metals and by an optimization of the alloying process, good surface morphology was obtained. The transmission-line model is used to extrapolate contact resistances from measurements on test patterns with multiple gap spacings varying from 1 to 10 μm. The nonalloyed contact resistance is found to be 0.025 Ω mm for a GaAs layer doped to 1×1018 with a 500-A(ring) graded InGaAs layer. Alloying the contact at 475 °C for 60 s produces a contact resistance of 0.019 Ω mm. This represents a substantial improvement over the contact resistances obtained by just using an ungraded cap layer of InAs on GaAs. Assuming that the sheet resistance under the contact is the same as the sheet resistance in the top semiconductor layer (this is not strictly true), the nominal value of the specific contact resistance for the nonalloyed situation is 5.32×10−7 Ω cm2, while for the alloyed case the specific contact resistance is 2.56×10−7 Ω cm2. The metal scheme used for the contact is Ni/Ge/Au/Ti/Au.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 5041-5044 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Wigner function simulations of structures with experimentally observed high peak-to-valley ratios are carried out. It is shown that if care is taken with the numerical method used, the simulations reproduce these sharp resonances. When scattering is ignored, peak-to-valley ratios of 33.7 are obtained for a pseudomorphic InGaAs-AlAs structure. The effects of phonon scattering are included to first order. Also, a small-signal analysis is carried out and the results are used to predict the rf power generation capability of these devices.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 7638-7639 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Switching speeds are calculated for GaAs-AlGaAs resonant-tunneling diode structures with different barrier widths from the time-dependent Schrödinger equation. The speed is determined by monitoring the device current as the bias voltage is instantaneously switched. Effective mass discontinuities at the barrier and quantum well edges are included. Comparisons with previously published results using the wave packet approach are given. It is found that the turn-off transient is dominated by the lifetime of the quasibound state; however, care must be used in calculating the lifetime.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 2340-2346 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A theoretical model for quantum well varactors is presented. The model is used to calculate the device C-V and I-V characteristics and very good agreement has been found between the calculated and measured results. Based on the model, a triple barrier double well varactor has been designed and fabricated. A very high capacitance ratio within a very small bias range is achieved, as designed. Details of the design calculations and experimental results are presented.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 1114-1122 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Injection over and through heterojunction barriers is becoming increasingly more important in modern electronic devices. We consider the properties of graded AlxGa1−xAs heterojunction barriers using a self-consistent ensemble Monte Carlo method. In this paper, we consider barriers with two doping levels, 1×1015 cm−3 and 1×1017 cm−3, and two barrier heights, 100 and 265 meV. The 100-meV barrier resulted in small rectification at room temperature whereas the higher barrier exhibited considerable rectification. In both cases the structure with the lower doped barrier has resulted in a smaller current in both forward and reverse regions due to space-charge effects. The energy and momentum distribution functions deviate from a Maxwellian distribution inside the barrier region and in general show two peaks: one is comprised mainly of electrons near equilibrium and the second arises mainly from ballistic electrons. The higher doped structure resulted in a faster electron relaxation toward equilibrium as a function of position because the electric field decreases rapidly in the barrier region.
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