Papers by Keyword: Quantum Well

Abstract: Description of theoretical model for energy-band spectrum calculation for the heteroepitaxial CdHgTe (MCT) structures grown by molecular-beam epitaxy (MBE) method with the single quantum wells (QW) is presented in this work. This computation model allows to calculate different electro-physical properties of this structures and allows to explain features of their C-V and G-V characteristics in the wide temperature range, i.e. from “helium” till room temperatures. This scientific work was carried out in the network of Tomsk State University Competitiveness Improvement Program.

Abstract: Indium Antimonide (InSb) has the greater electron mobility and saturation velocity of any semiconductor. Also InSb detectors are sensitive between 1–5 μm wavelengths and it belongs to III-V [13] component. In this paper we compare the InSb with some other major components like Indium Phosphide (InP) and Gallium Arsenide (GaAs) which are also from same III-V group. The analysis was made using the simulation tool TCAD and using the properties and band structure of those materials we compare InSb with InP and GaAs. The results we proposed shows that InSb is best for ultra high speed and very low power applications.

Abstract: Strain-balanced quantum well solar cells (SB-QWSC) extend the photon absorption edge beyond that of bulk GaAs by incorporation of quantum wells in the i-region of a pin device. The strain-balanced quantum well solar cell benefits from a fundamental efficiency enhancement due to anisotropic emission from the quantum wells. This anisotropy arises from a splitting of the valence band due to compressive strain in the quantum wells, suppressing a transition which contributes to emission from the edge of the quantum wells. We have studied both the emission light polarized in the plane perpendicular (TM) to the quantum well which couples exclusively to the light hole transition and the emission polarized in the plane of the quantum wells (TE) which couples mainly to the heavy hole transition. It was found that the spontaneous emission rates TM and TE increase when the quantum wells are deeper. We have also demonstrated that the photo-generated carriers can escape from the QWs with near unity efficiency, via a thermally-assisted tunneling process, because gain is several orders greater than radiative recombination.

Abstract: Effective magnetic field of nuclear spin polarization (NSP) under circularly polarized pumps excitation and the dephasing time of resident electron spin polarization under pump and control excitation has been detected in a single CdTe quantum well (QW) by a time-resolved Kerr rotation (TRKR) technique. We deduced that the experimental method is verified with the effect, to a certain extent, through confirming the external magnetic field results. In addition, the nuclear field is revealed to be increased with the increasing electron spin component due to the enhanced electron-nuclear hyperfine interaction. Significant nuclear field is observed as 1.85 mT with the applied magnetic field tilted by about 15 degree. What is more, we found the spin dephasing time (SDT) has little relation with the created NSP field, but it decreases largely with the increasing spin polarization magnitude under pump excitation and the spin vector dispersions induced by control pulses.

Abstract: The quantum-confined Stark effect on the optical absorption of intersubband transitions in an asymmetric Al_xGa_1-xN/In_0.3Ga_0.7N/GaN quantum wells is investigated by means of the density matrix formulism. The built-in electric field generated by the piezoelectric and spontaneous polarizations competing against to the external electric fields is considered. As the result, the influences of the built-in and external electric fields on the energy potentials and the eigen stares are discussed in detail. When the positive external electric field is applied, the peak values of the absorption coefficients from 3-2, 2-1 and 3-1 transitions are reduced and moved to the lower photon energy levels. With the negative field, the exactly opposite results can be obtained. Moreover, it is indicated that the results of the wavelengths from the 3-2, 2-1 and 3-1 transitions are reduced by the positive external electric field and increased by the negative field.

Abstract: The quantum confinement Stark effect of three types of GaInNAs quantum wells, namely single square quantum well, stepped quantum wells and coupled quantum wells, is investigated using the band anti-crossing model. The comparison between experimental observation and modeling result validate the modeling process. The effects of the external electric field and localized N states on the quantized energy shifts of these three structures are compared and analyzed. The external electric field applied to the QW not only changes the potential profile but also modulates the localized N states, which causes band gap energy shifts and increase of electron effective mass.

Abstract: We propose the one-dimensional photonic crystal quantum well structure composed of two negative metamaterials, the features of which are investigated with scattering matrix method. With this method, the transmittance, reflectance and dispersion relation of electromagnetic wave propagation in photonic crystal are obtained. Moreover, the photonic band structure is given by dispersion relation. For photonic crystal parallel wells the sandwich structure (M^pN^qM^p) and four PCs structure (M^pN^qM^pN^q), the resonant modes exist in the photonic band gaps. The number of resonant modes is varied by changing the period number of the constituent photonic crystals. Meanwhile, the resonant modes is not sensitive to the incident angle increasing, only shift slowly to lower frequency region. Moreover, the resonant modes can be act as multiple ultra-narrow bandwidth filters.

Abstract: The band structure and optical gain of a novel n⁺ doping tensile-strained Ge/GeSiSn quantum well are investigated by using an 8-band k·p method. The doping effect in Ge quantum well and the effect of the carrier leakage into L valley on the optical gain will also be considered. The E-k dispersion curves and optical gain spectra will be obtained and discussed.

Abstract: A dip-shaped InGaN/GaN quantum well (QW) structure was computed to design efficient light-emitting diodes (LEDs). The advanced LEDs designed with the dip-shaped QW structures exhibited higher internal quantum efficiency by 26 % and the lower temperature-driven efficiency droop as compared to the reference LEDs. This could be due to the enhanced radiative recombination rate in the QW active region, which is associated with the reduced spatial separation of electron-hole wave functions.

Abstract: This paper presents a comparative analysis of some of the important characteristics of the carriers of quantum well and quantum dot based laser. Among the characteristics of the carriers, confined carrier concentrations in the gain medium as well as the carrier concentrations at the threshold have been studied extensively by using In_xGa_1-xN based quantum well and In_xGa_1-xN based quantum dot in the active layer of the laser structure. The numerical results obtained are compared to investigate the superiority of the quantum dot over quantum well. It is ascertained from the comparison results that In_xGa_1-xN based quantum dot provides higher density of confined carrier and lower level of carrier concentration required for lasing action. This paper reports the enhancement of confined carrier density and minimization of carrier concentration at threshold of laser using In_xGa_1-xN based quantum dot as the active layer material. Hence, it is revealed that better performances of lasers have been obtained using In_xGa_1-xN based quantum dot than that of quantum well in the active medium of the device structure.