The exciton luminescence in Zn(Cd)Se/ZnMgSSe quantum wells

We study exciton states in Zn(Cd)Se/ZnMgSSe quantum wells (QWs) with various degrees of diffusion blurring in the interfaces by the methods of optical spectroscopy. We show that at low temperatures the QW emission spectra are determined by free and neutral donor-bound excitons. Blurring of the heterointerfaces leads to the increase in the energy shift between the emission line maxima of free and bound excitons. We explain the nonlinear dependence of the steady-state photoluminescence intensity on the excitation-power density in terms of the neutralization of charged donors at the photoexcitation of heterostructures. We observed a complex long-time dynamics of the reflection coefficient, evoked by the charge-redistribution processes in the heterostructure, near the QW exciton resonances under the irradiation.     

Features of the effect of heterointerface spreading on exciton states in Zn(Cd)Se/ZnMgSSe quantum wells

The exciton states in Zn(Cd)Se/ZnMgSSe quantum wells with various degrees of diffusive spreading of interfaces are studied by optical spectroscopy methods. Luminescence lines of free excitons are identified. It is shown that, in addition to exciton level shift, heterointerface spreading enhances exciton-phonon coupling and increases the energy shift between maxima of emission lines of free and bound excitons. The major causes of the observed phenomena are discussed.     

Effect of heteroboundary spreading on the properties of exciton states in Zn(Cd)Se/ZnMgSSe quantum wells

Exciton states in Zn(Cd)Se/ZnMgSSe quantum wells with different diffusion spreading of interfaces are studied by optical spectroscopy methods. It is shown that the emission spectrum of quantum wells at low temperatures is determined by free excitons and bound excitons on neutral donors. The nonlinear dependence of the stationary photoluminescence intensity on the excitation power density and the biexponential luminescence decay are explained by the neutralization of charged defects upon photoexcitation of heterostructures. With the stationary illumination on, durable (about 40 min) reversible changes in the reflection coefficient near the exciton resonances of quantum wells are observed. It is shown that, along with the shift of exciton levels, the spreading of heteroboundaries leads to three effects: an increase in the excitonphonon interaction, an increase in the energy shift between the emission lines of free and bound excitons, and a decrease in the decay time of exciton luminescence in a broad temperature range. The main reasons for these effects are discussed.     

Experimental evidence of the exciton centre-of-mass quantization in Zn1−x Cd x Se/ZnSe multiple quantum wells

Il Nuovo Cimento D - We report the evidence of exciton-polariton centre-of-mass quantization in II–VI quantum wells consisting of ternary alloy. Absorption and photoluminescence studies on...     

Optically detected magnetic resonance of Mn-related excitations in (Cd,Mn)Te quantum wells

Optically detected magnetic resonance (ODMR) was applied to reveal the exchange interaction effects between Mn²⁺ ions and confined holes in (Cd,Mn)Te quantum wells with 2D hole gas. Two anisotropic ODMR signals with different angular variations were found and ascribed to isolated manganese ions and to exchange-coupled complexes consisting of manganese and holes. It is shown that calculations on the basis of spin Hamiltonian for these systems are in agreement with the experimental data.     

The quantum confinement effect observed in the multiple quantum wells Mg0.27Zn0.73O/ZnO

The multiple quantum wells (MQW) Mg_0.27Zn_0.73O/ZnO have been grown by pulsed laser deposition method with different well width L _w . The optical and structural characteristics of MQW Mg_0.27Zn_0.73O/ZnO have been investigated. The quantum confinement effect showing up in the blue shift of exciton peak in low temperature (8 K) photoluminescence spectra at well width reduction has been studied. It is established that intensity exciton peak I _ex and Einstein’s characteristic temperature Θ _E increase at reduction of well width L _w . It is revealed that the discontinuity ratio of conduction and a valence bands in heterostructure Mg_0.27Zn_0.73O/ZnO is 0.65/0.35 that corresponds to the literature.     

Polaritons in large-period multiple quantum wells

Il Nuovo Cimento D - Experimental studies of high-resolution reflectivity and a temperature dependence of the photoluminescence for periodic MQWs of CdTe/CdZnTe with periods equal to a one-half and...     

Optical vibration modes in (Cd,Pb, Zn)S quantum dots in the Langmuir-Blodgett matrix

The structures with CdS, PbS, and ZnS quantum dots produced using the Langmuir-Blodgett method are investigated by infrared (IR) spectroscopy, Raman scattering, and ultraviolet (UV) spectroscopy. The quantum dot size estimated from the UV spectra and high-resolution transmission electron microscopy (HRTEM) falls in the range 2–6 nm. The longitudinal optical (LO) phonons localized in quantum dots and the surface optical vibration modes are revealed in the IR reflection and Raman scattering spectra of the structures under investigation. The frequencies of the surface optical modes are adequately described with allowance made for the effect of localizing optical phonons in the quantum dots.