207 research outputs found
Optical properties of potential-inserted quantum wells in the near infrared and Terahertz ranges
We propose an engineering of the optical properties of GaAs/AlGaAs quantum
wells using AlAs and InAs monolayer insertions. A quantitative study of the
effects of the monolayer position and the well thickness on the interband and
intersubband transitions, based on the extended-basis sp3d5s* tight-binding
model, is presented. The effect of insertion on the interband transitions is
compared with existing experimental data. As for intersubband transitions, we
show that in a GaAs/AlGaAs quantum well including two AlAs and one InAs
insertions, a three level {e1 , e2 , e3 } system where the transition energy
e3-e2 is lower and the transition energy e2-e1 larger than the longitudinal
optical phonon energy (36 meV) can be engineered together with a e3-e2
transition energy widely tunable through the TeraHertz range
Interplay between disorder and intersubband collective excitations in the two-dimensional electron gas
Intersubband absorption in modulation-doped quantum wells is usually
appropriately described as a collective excitation of the confined
two-dimensional electron gas. At sufficiently low electron density and low
temperatures, however, the in-plane disorder potential is able to damp the
collective modes by mixing the intersubband charge-density excitation with
single-particle localized modes. Here we show experimental evidence of this
transition. The results are analyzed within the framework of the density
functional theory and highlight the impact of the interplay between disorder
and the collective response of the two-dimensional electron gas in
semiconductor heterostructures.Comment: 5 pages, 4 figures, RevTeX. Accepted for publication in Phys. Rev. B
(Rapid. Comm.
Self-consistent analysis of carrier-transport and carrier-capture dynamics in quantum cascade intersubband semiconductor lasers
A methodology for the self-consistent analysis of carrier transport and carrier capture aspects of the dynamics of quantum cascade intersubband semiconductor lasers is described in this paper. The approach is used to analyze two prototype quantum cascade lasers. The self-consistent analysis incorporates the calculation of the electron densities and temperatures in each subband, together with the intersubband relaxation time. In the calculation of the relaxation time, we take into account the electron interaction with polar optical and acoustic phonons, as well as electron degeneracy. In addition, we also calculate the capture time, considering backward processes that play a role in the electron transition from an injection into an active region. The calculations indicate intersubband relaxation times of order 1 ps and capture times of order 100 f
Electricâfield dependence of interband transitions in In_(0.53)Ga_(0.47)As/In_(0.52)Al_(0.48)As single quantum wells by roomâtemperature electrotransmittance
Roomâtemperature electrotransmittance has been used in order to investigate the interband excitonic transitions in a 250âĂ
âthick In_(0.53)Ga_(0.47)As/In_(0.52)Al_(0.48)As singleâquantumâwell system as a function of an externally applied electric field. Parity forbidden transitions, involving conductionâband states with quantum numbers up to n=5, which become more pronounced at high electric fields were observed. The groundâstate and the forbidden transitions showed a significant red shift due to the quantum confined Stark effect. A comparison with previously reported results on thinner InGaAs/InAlAs quantum wells indicated that the wideâwell sample exhibits the largest shift, as expected from theory. Despite the appreciable Stark shift, the rather large, fieldâinduced linewidth broadening and the relatively low electric field at which the groundâstate exciton is ionized poses limitations on using this wideâquantumâwell system for electroâoptic applications
Dilute magnetic semiconductor quantum-well structures for magnetic field tunable far-infrared/terahertz absorption
The design of ZnCdSeâZnMnSe-based quantum
wells is considered, in order to obtain a large shift of the peak absorption wavelength in the far infrared range, due to a giant Zeeman splitting with magnetic field, while maintaining a reasonably large value of peak absorption. A triple quantum-well structure with a suitable choice of parameters has been found to satisfy such requirements. A maximal tuning range between 14.6 and 34.7 meV is obtained, when the magnetic field varies from zero
to 5 T, so the wavelength of the absorbed radiation decreases from 85.2 to 35.7 ÎŒm with absorption up to 1.25% at low temperatures. These structures might form the basis for magnetic field tunable photodetectors and quantum cascade lasers in the terahertz range
Second harmonic generation at the quantum-interference induced transparency in semiconductor quantum wells: The influence of permanent dipole moments
The influence of permanent dipole moments of quantized
states on intersubband second harmonic generation based
on quantum-interference induced transparency in semiconductor quantum wells is explored using the harmonic balance method. The permanent moments are found to be quite important: they affect the transparency condition, especially at larger pump intensities. Hence, both the conversion efficiency and the optimal interaction
path length change significantly when accounting for the permanent moments, and the conversion efficiency is reduced
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