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 Physics , 2000, DOI: 10.1103/PhysRevB.62.15390 Abstract: We study the evolution of the absorption spectrum of a modulation doped GaAs/AlGaAs semiconductor quantum well with decreasing the carrier density. We find that there is a critical density which marks the transition from a Fermi edge singularity to a hydrogen-like behavior. At this density both the lineshape and the transitions energies of the excitons change. We study the density dependence of the singularity exponent $\alpha$ and show that disorder plays an important role in determining the energy scale over which it grows.
 中国物理 B , 2009, Abstract: The influence of applied electric fields on the absorption coefficient and subband distances in asymmetrical AlN/GaN coupled double quantum wells (CDQWs) has been investigated by solving Schr?dinger and Poisson equations self-consistently. It is found that the absorption coefficient of the intersubband transition (ISBT) between the ground state and the third excited state (1odd-2even) can be equal to zero when the electric fields are applied in asymmetrical AlN/GaN CDQWs, which is related to applied electric fields induced symmetry recovery of these states. Meanwhile, the energy distances between 1odd-2even and 1even-2even subbands have different relationships from each other with the increase of applied electric fields due to the different polarization-induced potential drops between the left and the right wells. The results indicate that an electrical-optical modulator operated within the opto-communication wavelength range can be realized in spite of the strong polarization-induced electric fields in asymmetrical AlN/GaN CDQWs.
 - , 2016, Abstract: 在有效质量近似下，详细研究了直接带隙Ge/GeSi耦合双量子阱中带间光跃迁吸收系数和阈值能量随量子阱结构参数的变化情况。结果表明：随着量子阱阱宽增大，带间光跃迁吸收强度会逐渐减弱，阈值能量减小，吸收曲线向低能方向移动，出现了红移现象。增强耦合量子阱间的耦合效应使得带间光吸收强度显著提升。此外，与非对称耦合量子阱相比，耦合效应对对称耦合量子阱中光吸收系数的影响更为显著。Within the framework of the effective-mass approximation, we study the dependences of the interband optical absorption coefficient and threshold energy on the structure parameters of the direct-gap Ge/GeSi double coupled quantum wells. It is found that when the well width is increased, the intensity of the interband optical absorption is reduced. Moreover, the threshold energy is decreased and the absorption peak is moved towards the lower energy. Red shift is observed. The intensity of the interband optical absorption increases considerably with the increasing of the coupling effects between the quantum wells. Furthermore, in comparison to the asymmetry double quantum wells, the coupling effects on the optical absorption coefficient are more significant in the symmetric double coupled quantum wells.
 李素梅,郑卫民,宋迎新,刘静,初宁宁 中国物理 B , 2009, Abstract: This paper studies the dynamics of intra-acceptor hole relaxation in Be δ -doped GaAs/AlAs multiple quantum wells (MQW) with doping at the centre by time-resolved pump-probe spectroscopy using a picosecond free electron laser for infrared experiments. Low temperature far-infrared absorption measurements clearly show three principal absorption lines due to transitions of the Be acceptor from the ground state to the first three odd-parity excited states respectively. The pump-probe experiments are performed at different temperatures and different pump pulse wavelengths. The hole relaxation time from 2p excited state to 1s ground state in MQW is found to be much shorter than that in bulk GaAs, and shown to be independent of temperature but strongly dependent on wavelength. The zone-folded acoustic phonon emission and slower decay of the wavefunctions of impurity states are suggested to account for the reduction of the 2p excited state lifetime in MQW. The wavelength dependence of the 2p lifetime is attributed to the diffusion of the Be atom δ -layer in quantum wells.
 Nguyen Quang Bau;Do Manh Hung;Le Thai Hung PIER Letters , 2010, DOI: 10.2528/PIERL10030911 Abstract: The influences of confined phonons on the nonlinear absorption coefficient (NAC) by a strong electromagnetic wave for the case of electron-optical phonon scattering in doped superlattices (DSLs) are theoretically studied by using the quantum transport equation for electrons. The dependence of NAC on the energy (), the amplitude () of external strong electromagnetic wave, the temperature (T) of the system, is obtained. Two cases for the absorption: Close to the absorption threshold ∣ - ∣<< and far away from the absorption threshold ∣ - ∣>> (k = 0, 1, 2..., and are the frequency of optical phonon and the average energy of electrons, respectively) are considered. The formula of the NAC contains a quantum number m characterizing confined phonons. The analytic expressions are numerically evaluated, plotted and discussed for a specific of the n-GaAs/p-GaAs DSLs. The computations show that the spectrums of the NAC in case of confined phonon are much different from they are in case of un-confined phonon and strongly depend on a quantum number m characterizing confinement phonon.
 Hoang Dinh Trien;N. V. Nhan PIER Letters , 2011, DOI: 10.2528/PIERL10110910 Abstract: The nonlinear absorption of a strong electromagnetic wave caused by electrons confined in cylindrical quantum wires is theoretically studied by using the quantum kinetic equation for electrons. An analytic expression of the nonlinear absorption coefficient of a strong electromagnetic wave caused by electrons confined in a cylindrical quantum wire with a parabolic potential for electron-optical phonon scattering is obtained. The dependence of the nonlinear absorption coefficient on the intensity and the frequency of the external strong electromagnetic wave, the temperature T of the system and the radius of the wires is strong and nonlinear. Analytic expression is numerically calculated and discussed for a quantum wire. The results are compared with those for normal bulk semiconductors and quantum wells to show the differences.
 中国物理快报 , 2004, Abstract: We have calculated the intraband photon absorption coefficients of hot two-dimensional electrons interacting with polar-optical phonon modes in quantum wells. The dependence of the photon absorption coefficients on the photon wavelength λ is obtained both by using the quantum mechanical theory and by the balance-equation theory. It is found that the photon absorption spectrum displays a local resonant maximum, corresponding to LO energy, and the absorption peak vanishes with increasing the electronic temperature.
 AIP Advances , 2011, DOI: 10.1063/1.3646149 Abstract: Germanium has become a promising material for creating CMOS-compatible optoelectronic devices, such as modulators and detectors employing the Franz-Keldysh effect (FKE) or the quantum-confined Stark effect (QCSE), which meet strict energy and density requirements for future interconnects. To improve Ge-based modulator design, it is important to understand the contributions to the insertion loss (IL). With indirect absorption being the primary component of IL, we have experimentally determined the strength of this loss and compared it with theoretical models. For the first time, we have used the more sensitive photocurrent measurements for determining the effective absorption coefficient in our Ge/SiGe quantum well material employing QCSE. This measurement technique enables measurement of the absorption coefficient over four orders of magnitude. We find good agreement between our thin Ge quantum wells and the bulk material parameters and theoretical models. Similar to bulk Ge, we find that the 27.7 meV LA phonon is dominant in these quantum confined structures and that the electroabsorption profile can be predicted using the model presented by Frova, Phys. Rev., 145 (1966).
 Physics , 2009, DOI: 10.1103/PhysRevB.81.085320 Abstract: Recent experiments have demonstrated long spin lifetimes in uniformly n-doped quantum wells. The spin dynamics of exciton, localized, and conduction spins are important for understanding these systems. We explain experimental behavior by invoking spin exchange between all spin species. By doing so we explain quantitatively and qualitatively the striking and unusual temperature dependence in (110)-GaAs quantum wells. We discuss possible future experiments to resolve the pertinent localized spin relaxation mechanisms. In addition, our analysis allows us to propose possible experimental scenarios that will optimize spin relaxation times in GaAs and CdTe quantum wells.
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