Stability of Excited Exciton States in Semiconductor Quantum Dots Under a Lateral Electric Field

The effect of the lateral electric field (LEF) on the excited and ground state stability of an exciton ([Formula: see text]) confined in a parabolic cylindrical quantum dot (QD) was estimated in this study. The calculation was performed in the framework of single-band effective mass theory using a variational approach. Our results revealed that the ground state binding energy of [Formula: see text] decreases with increasing the cylindrical QD radius until the exciton stability is lost at moderate LEF strength. By increasing the LEF strength, the excited heavy-hole ([Formula: see text]) can create an excited state [Formula: see text] or excited state [Formula: see text] of [Formula: see text], and the results indicate that the first state is more stable. In contrast, when an excited electron ([Formula: see text]) combines with an excited hole ([Formula: see text]) or unexcited hole ([Formula: see text]), it contains no split excited states for [Formula: see text] with less binding energy than the state [Formula: see text]. Comparing our previous results of donor impurity [Formula: see text] with [Formula: see text], we found that [Formula: see text] has a more stable ground state than [Formula: see text]. Moreover, the excited [Formula: see text] states are more stable than the excited states of [Formula: see text]. The quantum Stark shift (QSS) of the light- and heavy-hole exciton energy was explored, and a blue-shifted and quadratic QSS was observed. In contrast, for single particles (electron, heavy-hole and light hole), a red-shifted and linear QSS was observed.

Excitonic States and Related Optical Susceptibility in InN/AlN Quantum Well Under the Effects of the Well Size and Impurity Position

Based on the finite difference method, linear optical susceptibility, photoluminescence peak and binding energies of three first states of an exciton trapped by a positive charge donor-impurity ( ) confined in InN/AlN quantum well are investigated in terms of well size and impurity position. The electron, heavy hole free and bound excitons allowed eigen-values and corresponding eigen-functions are obtained numerically by solving one-dimensional time-independent Schrödinger equation. Within the parabolic band and effective mass approximations, the calculations are made considering the coupling of the electron in the n-th conduction subband and the heavy hole in the m-th valence subband under the impacts of the well size and impurity position. The obtained results show clearly that the energy, binding energy and photoluminescence peak energy show a decreasing behavior according to well size for both free and bound cases. Moreover, the optical susceptibility associated to exciton transition is strongly red-shift (blue-shifted) with enhancing the well size (impurity position).

Photoluminescence properties of GaAsBi single quantum wells with 10% of Bi

A set of single quantum well (SQW) samples of GaAs1-xBix with x ~ 0.1 and p-doped GaAs barriers grown by molecular beam epitaxy was investigated by the temperature-dependent photoluminescence (PL) spectroscopy. Those GaAsBi SQW structures showed a high crystalline quality, a smooth surface and sharp interfaces between the layers and exhibited a high PL intensity and a lower than 100 meV PL linewidth of QW structures. Temperature dependence of the optical transition energy was S-shape-free for all investigated structures and it was weaker than that of GaAs. An analysis of the carrier recombination mechanism was also carried out indicating that the radiative recombination is dominant even at room temperature. Moreover, numerical calculations revealed that a higher Be doping concentration leads to an increased overlap of the electron and heavy hole wave functions and determines a higher PL intensity.

Ensemble Monte Carlo Simulation of Hole Transport in SiGe Alloys

This paper employs Ensemble Monte Carlo method to simulate transport of holes in SiGe alloys. A three-band model was employed to describe the valence band of these alloys. The nonparabolicity and the warping effect of the heavy-hole and light-hole bands were considered in their dispersion relation, while the split-off band was described as parabolic and spherical. We consider phonon and alloy disorder scattering in these calculations. The mobility of holes for a range of SiGe al-loys was calculated at 300K. The simulation mobility results agree with the experimental data, implying that the selected transport model for holes in SiGe alloys is adequate.

Нетривиальная зависимость спектральных характеристик экситонов в квантовых ямах от мощности резонансного оптического возбуждения

Basic exciton parameters, the energy of exciton transition and the radiative and nonradiative broadenings, are experimentally studied by means of reflectance spectroscopy for a heterostructure with the 14-nm GaAs/AlGaAs quantum well. Particular attention is paid to the nonradiative broadening which is sensitive to optical creation of free carriers and long-lived nonradiative excitons. A sublinear increase of the broadening of the heavy-hole and light-hole exciton resonances is observed when the light-hole exciton resonance is excited with increasing power. A simple model is developed, which allows one to well reproduce the observed dependence.

Stress and strain effects

This chapter extends this book’s discussion of bandstructure, band discontinuities and transport—much of the text up to this point—to a manipulation of them through stress and strain. Semiconductors can be strained through a variety of techniques, with strained growth leading to a strained layer, and pattern definition leading to local strained region, being the most common. Strain changes bandstructures and interface bandedge energies, distorts and warps bands, removes degeneracies, affects scattering and thus changes a variety of properties. Following a continuum description of stress-strain relationships, effects of stress—biaxial, hydrostatic and uniaxial—are analyzed for bandstructure and transport in electron bands, light-hole bands, heavy-hole bands and split-off bands in group IV and group III-V semiconductors. Transport effects can be particularly strong in quantum-confined conditions, where changes in density of states can be significant, along with other bandstructure and scattering changes.