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  • 1
    Electronic Resource
    Electronic Resource
    Self-consistent calculation of the electronic structure of semiconductor quantum wires: Semiclassical and quantum mechanical approaches (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 6234-6241 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Efficient self-consistent calculations of dynamically one-dimensional electron gas systems using the finite element method with nonuniform mesh of triangular elements have been implemented. Both self-consistent semiclassical and self-consistent quantum mechanical calculations are carried out. In the semiclassical treatment, Poisson's equation is solved self-consistently with the induced electron density determined by the Thomas–Fermi continuum formalism. Newton's method is implemented to ensure fast convergence. In the quantum mechanical treatment, quasi-one-dimensional subband levels are determined by solving the effective mass Schrödinger equation and the induced electron density is determined by filling the occupied subbands according to Fermi–Dirac statistics for zero temperature. Self-consistency is achieved using Newton's method with an approximate Jacobian derived from the Thomas–Fermi approximation. Etched ridge and split gate semiconductor quantum wires based on selectively doped AlGaAs/GaAs heterostructures are studied. The results of the semiclassical and quantum mechanical calculations are compared. We find that the two approaches predict similar lineal densities of induced electrons for a range of cases but that the dependence of electron density on external parameters can differ significantly. The resulting potential shapes and electron distributions can also be quite different. Specifically, the semiclassical approach results in shallower confining potential wells and less spread of the electron distribution in the direction perpendicular to the heterointerface than is found in the quantum mechanical approach.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355197
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  • 2
    Electronic Resource
    Electronic Resource
    Exchange effect in coupled one-dimensional electron-gas systems (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 1318-1321 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An exchange effect in one-dimensional quantum-wire electron-gas systems is investigated. The theoretical study presented shows that the electron population of a symmetrical structure consisting of two parallel quantum wires in close proximity may exhibit bistability with all electrons contained in one of the quantum wires. Compared to a similar effect in a two-dimensional system reported earlier, the excitation energy associated with the transfer of one electron is found to be much larger. For certain configurations, this energy can be as large as ∼50 meV. The theory predicts the exchange-induced bistability to exist in realistic configurations, and it may possibly be used in practical electronic devices such as memory elements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351249
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  • 3
    Electronic Resource
    Electronic Resource
    Channel formation in organic field-effect transistors (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 4312-4318 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results of two-dimensional electrostatic modeling of organic field-effect transistors, focusing on the formation of the conductive channel, are reported. The effect on channel formation of the choice of the source and drain contact metal is investigated for both top- and bottom-contact device structures. High-work-function metal (e.g., gold) source and drain contacts produce a conducting p-type region near these contacts. In contrast, low-work-function metal source and drain contacts (e.g., magnesium) lead to depleted regions. In the center of the device, between the source and drain contacts, the channel carrier density at a fixed gate bias is determined by the work function of the gate contact material, and is essentially independent of the metal used to form the source and drain contacts. The principal difference between top- and bottom-contact structures is the spatial variation of the charge density in the vicinity of the source and drain contacts. The channel carrier density for a fixed gate bias (and gate contact material) between the source and drain electrodes is essentially the same for the two structures. Finally, the dependence of the transistor threshold voltage on the gate contact metal work function and the device implications of the spatial variation of the induced charge density are discussed. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1453509
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  • 4
    Electronic Resource
    Electronic Resource
    Modeling of band-to-band tunneling transitions during drift in Monte Carlo transport simulations (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 1488-1493 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The conventional method of semiconductor charge carrier transport investigations using full band ensemble Monte Carlo simulations is extended to allow for tunneling between bands during accelerated drift of the carriers. The essentially classical picture of transport, as simulated, is preserved by implementing a stochastic selection of the band index of the initial state of each scattering process associated with phonons, with impurities, or with impact ionization. Relative probabilities for the band assignment are calculated from the overlap integrals of the cell-periodic parts of Bloch wave functions belonging to different bands, for k-vectors along the carrier k-space trajectory between successive scattering events. As an example, the method is applied to Monte Carlo transport simulations for holes in 4H SiC in a homogeneous applied electric field. Tunneling between valence bands during the drift phases is shown to have a significant impact on the carrier energy distributions when large electric fields are applied, and on physical parameters that directly depend on the carrier energy, such as the hole initiated impact ionization coefficient. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373844
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  • 5
    Electronic Resource
    Electronic Resource
    High field electron transport properties of bulk ZnO (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 6864-6867 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Monte Carlo method is used to simulate electron transport for electric field strengths up to 350 kV/cm in bulk, wurtzite structure ZnO. The relevant parts of the conduction bands of a first-principles band structure are approximated by spherically symmetric, nonparabolic valleys located at the Γ and Umin symmetry points of the Brillouin zone. It is shown that the analytic expressions represent the band structure and the density of states well over a range of nearly 5 eV from the bottom of the conduction band. The simulated electron steady-state drift velocity versus electric field characteristics are calculated for lattice temperatures of 300, 450, and 600 K. For room temperature, drift velocities higher than 3×107 cm/s are reached at fields near 250 kV/cm. Examination of the electron energy distributions shows that the strong decrease of the differential mobility with increasing electric field in the field range studied is to be associated with the pronounced nonparabolicity of the central valley and not with transfer of electrons to satellite valleys. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371764
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  • 6
    Electronic Resource
    Electronic Resource
    AlGaN/GaN heterojunction bipolar transistor structures-design considerations (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 1067-1072 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The potential of III-nitride materials for the fabrication of bipolar transistors is investigated theoretically. Several different AlGaN/GaN n–p–n heterojunction bipolar transistor structures are examined through calculations of their band profiles and majority carrier distributions in equilibrium and in forward active mode. Spontaneous and piezoelectric polarization charges are utilized to create large hole sheet carrier densities in the base layer, thus minimizing the base spreading resistance. At the same time, a large accelerating field in the base can help reduce the base transit time of the electrons and, hence, increase the current gains of these devices. The temperature dependence of the hole concentration in the base is also investigated. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373778
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  • 7
    Electronic Resource
    Electronic Resource
    Hole transport properties of bulk zinc-blende and wurtzite phases of GaN based on an ensemble Monte Carlo calculation including a full zone band structure (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 4429-4436 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper, we present calculations of the hole transport properties of bulk zinc-blende and wurtzite phase GaN at field strengths at which impact ionization does not occur significantly. The calculations are made using an ensemble Monte Carlo simulator, including the full details of the band structure and a numerically determined phonon scattering rate based on an empirical pseudopotential method. Band intersection points—including band crossings and band mixings—are treated by carefully evaluating the overlap integral between the initial and possible final drift states. In this way, the hole trajectories in phase space can be accurately traced. It is found that the average hole energies are significantly lower than the corresponding electron energies for the field strengths examined. This result is most probably due to the drastic difference in curvature between the uppermost valence bands and the lowest conduction band. The relatively flat valence bands impede hole-heating, leading to low average hole energy. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363422
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  • 8
    Electronic Resource
    Electronic Resource
    Linear in-plane uniaxial stress effects on the device characteristics of AlGaAs/GaAs modulation doped field effect transistors (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 502-505 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The current voltage relationships of AlGaAs/GaAs modulation doped field effect transistors (MODFETs) were measured as a function of applied uniaxial stress. Stresses in the [110] and [11¯0] directions on MODFETs that were grown on a (001) substrate produced threshold shifts of opposite sign. Stresses in [110] and [11¯0] directions resulted in threshold voltage pressure coefficients of −15 and 64 mV/Kbar, respectively. The asymmetric shifts in the threshold voltages are attributed to piezoelectric effects. In addition, stress induced changes in the slopes of the transconductance versus gate-to-source voltage relationships were also measured. For stresses in the [110] and [11¯0] directions, the dependencies were 0.4 and −0.7 mS/(VKbar), respectively.© 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364126
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  • 9
    Electronic Resource
    Electronic Resource
    Electronic structure of dual gate quantum wire (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 2517-2521 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electronic structure of a novel nanometer scale semiconductor quantum wire structure [S. Y. Chou and Y. Wang, Appl. Phys. Lett. 63, 788 (1993)] has been calculated self-consistently. The structure has two control parameters, the voltage applied to a split gate and the voltage applied to a wire gate. The influences of both the split gate and the narrow wire gate which is placed inside the gap of the split gate, on the electronic structure of the system are examined. We show that varying the voltage on either the split gate or the wire gate changes the induced quantum wire confinement potential profile, the energy level spacing, the channel electron density, and the effective channel width. Results for the ballistic conductance of the device as a function of the two control voltages are extracted from the electronic structure calculations and are found to be in satisfactory agreement with experimental data. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361116
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  • 10
    Electronic Resource
    Electronic Resource
    Piezoelectric effect in (001)- and (111)-oriented double-barrier resonant tunneling devices (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 7770-7774 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We show experimentally that current–voltage characteristics of double-barrier resonant tunneling devices (DBRTDs) can be modified by internal polarization fields due to the piezoelectric effect induced by external uniaxial stresses. Electric polarization fields, perpendicular to the interfaces, arise in DBRTDs grown on (001)-oriented substrates under uniaxial, compressive stresses parallel to the (110) or (11¯0) crystal orientations, and in DBRTDs grown on (111)B-oriented substrates under stress parallel to (111) crystal orientation. The voltages at which the resonant tunneling current peaks occur (peak voltages) are sensitive to the polarization fields induced by external stresses. The peak voltages can shift to more positive voltages or more negative voltages depending on the directions of applied stresses. We measured current–voltage characteristics of AlAs/GaAs/AlAs double-barrier resonant tunneling structures as a function of external stresses at 77 K. Uniaxial stress was applied parallel to the (110) and the (11¯0) crystal orientations for (001)-oriented DBRTDs, as well as to the (111) orientation for (111)B-oriented DBRTDs. With the substrates grounded in all the measurements, we found that the peak voltages shift to more positive voltages for (001)-oriented DBRTDs under stress along the (110) orientation and for (111)-oriented DBRTDs under the stress along (111) orientation, and to more negative voltages for (001)-oriented devices under stress along the (11¯0) orientation. The results are in agreement with our calculations published in the preceding article, which take into account the piezoelectric effect and band alignment under stress. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362382
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