764 research outputs found
Scattering states of a particle, with position-dependent mass, in a double heterojunction
In this work we obtain the exact analytical scattering solutions of a
particle (electron or hole) in a semiconductor double heterojunction -
potential well / barrier - where the effective mass of the particle varies with
position inside the heterojunctions. It is observed that the spatial dependence
of mass within the well / barrier introduces a nonlinear component in the plane
wave solutions of the continuum states. Additionally, the transmission
coefficient is found to increase with increasing energy, finally approaching
unity, whereas the reflection coefficient follows the reverse trend and goes to
zero.Comment: 7 pages, 6 figure
InAs-GaSb laser: Prospects for efficient THz emission
We suggest to use InAs/GaSb coupled quantum wells for THz lasing. In these
heterostructures THz lasing is based not on intersubband but on interband
transitions. Crucial advantages of this design in comparison with intersubband
lasers are (i) a large value of the interband dipole matrix element and (ii)
easier maintaining of population inversion. These advantages lead to a gain of
two orders of magnitude higher than for intersubband lasing. Even higher gain
can be obtained in special design InAs/GaSb W-structures where a hybridization
gap of 1-3THz is formed and optical density of states is singular.Comment: 14 pages, 2 figures. Accepted for publication in Applied Physics
Letter
Exact solution of Schrodinger equation for modified Kratzer's molecular potential with the position-dependent mass
Exact solutions of Schrodinger equation are obtained for the modified Kratzer
and the corrected Morse potentials with the position-dependent effective mass.
The bound state energy eigenvalues and the corresponding eigenfunctions are
calculated for any angular momentum for target potentials. Various forms of
point canonical transformations are applied. PACS numbers: 03.65.-w; 03.65.Ge;
12.39.Fd Keywords: Morse potential, Kratzer potential, Position-dependent mass,
Point canonical transformation, Effective mass Schr\"{o}dinger equation.Comment: 9 page
Charge qubits in semiconductor quantum computer architectures: Tunnel coupling and decoherence
We consider charge qubits based on shallow donor electron states in silicon
and coupled quantum dots in GaAs. Specifically, we study the feasibility of
P charge qubits in Si, focusing on single qubit properties in terms of
tunnel coupling between the two phosphorus donors and qubit decoherence caused
by electron-phonon interaction. By taking into consideration the multi-valley
structure of the Si conduction band, we show that inter-valley quantum
interference has important consequences for single-qubit operations of P
charge qubits. In particular, the valley interference leads to a
tunnel-coupling strength distribution centered around zero. On the other hand,
we find that the Si bandstructure does not dramatically affect the
electron-phonon coupling and consequently, qubit coherence. We also critically
compare charge qubit properties for Si:P and GaAs double quantum dot
quantum computer architectures.Comment: 10 pages, 3 figure
Scattering states of a particle, with position-dependent mass, in a symmetric heterojunction
The study of a particle with position-dependent effective mass (pdem), within
a double heterojunction is extended into the complex domain --- when the region
within the heterojunctions is described by a non Hermitian
symmetric potential. After obtaining the exact analytical solutions, the
reflection and transmission coefficients are calculated, and plotted as a
function of the energy. It is observed that at least two of the characteristic
features of non Hermitian symmetric systems --- viz., left / right
asymmetry and anomalous behaviour at spectral singularity, are preserved even
in the presence of pdem. The possibility of charge conservation is also
discussed.Comment: 12 pages, including 6 figures; Journal of Physics A : Math. Theor.
(2012
Longitudinal spin transport in diluted magnetic semiconductor superlattices: the effect of the giant Zeeman splitting
Longitudinal spin transport in diluted magnetic semiconductor superlattices
is investigated theoretically. The longitudinal magnetoconductivity (MC) in
such systems exhibits an oscillating behavior as function of an external
magnetic field. In the weak magnetic field region the giant Zeeman splitting
plays a dominant role which leads to a large negative magnetoconductivity. In
the strong magnetic field region the MC exhibits deep dips with increasing
magnetic field. The oscillating behavior is attributed to the interplay between
the discrete Landau levels and the Fermi surface. The decrease of the MC at low
magnetic field is caused by the exchange interaction between the electron
in the conduction band and the magnetic ions.Comment: 6 pages, 9 figures, submitted to Phys. Rev.
Interband electron Raman scattering in a quantum wire in a transverse magnetic field
Electron Raman scattering (ERS) is investigated in a parabolic semiconductor
quantum wire in a transverse magnetic field neglecting by phonon-assisted
transitions. The ERS cross-section is calculated as a function of a frequency
shift and magnetic field. The process involves an interband electronic
transition and an intraband transition between quantized subbands. We analyze
the differential cross-section for different scattering configurations. We
study selection rules for the processes. Some singularities in the Raman
spectra are found and interpreted. The scattering spectrum shows
density-of-states peaks and interband matrix elements maximums and a strong
resonance when scattered frequency equals to the "hybrid" frequency or
confinement frequency depending on the light polarization. Numerical results
are presented for a GaAs/AlGaAs quantum wire.Comment: 8 pages, 5 figure
Measurement of miniband parameters of a doped superlattice by photoluminescence in high magnetic fields
We have studied a 50/50\AA superlattice of GaAs/AlGaAs
composition, modulation-doped with Si, to produce
cm electrons per superlattice period. The modulation-doping was tailored
to avoid the formation of Tamm states, and photoluminescence due to interband
transitions from extended superlattice states was detected. By studying the
effects of a quantizing magnetic field on the superlattice photoluminescence,
the miniband energy width, the reduced effective mass of the electron-hole
pair, and the band gap renormalization could be deduced.Comment: minor typing errors (minus sign in eq. (5)
Effect of in-plane magnetic field on the photoluminescence spectrum of modulation-doped quantum wells and heterojunctions
The photoluminescence (PL) spectrum of modulation-doped GaAs/AlGaAs quantum
wells (MDQW) and heterojunctions (HJ) is studied under a magnetic field
() applied parallel to the two-dimensional electron gas (2DEG) layer.
The effect of strongly depends on the electron-hole separation
(), and we revealed remarkable -induced modifications of the PL
spectra in both types of heterostructures. A model considering the direct
optical transitions between the conduction and valence subband that are shifted
in k-space under , accounts qualitatively for the observed spectral
modifications. In the HJs, the PL intensity of the bulk excitons is strongly
reduced relatively to that of the 2DEG with increasing . This means
that the distance between the photoholes and the 2DEG decreases with increased
, and that free holes are responsible for the hole-2DEG PL.Comment: 6pages, 5figure
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