xMnxTe Multiple Quantum Wells Research Articles

Time-Resolved Nonlinear Faraday Rotation in Semimagnetic Quantum Wells

We investigate the dynamics of the Faraday rotation angle by means of time-resolved pump/probe experiments in CdTe/Cd1—xMnxTe multiple quantum wells under high excitation conditions. During the first step of the optical excitation, stimulated emission and amplification of the Faraday rotation is observed. Spectrally resolved measurements reveal that large photoinduced rotation changes can be achieved when the frequency is tuned close to the excitonic resonance and saturation sets in.

Magnetic-field induced type I-type II transition in [formula omitted] multiple quantum wells

A magneto-absorption measurement up to 150 T was performed on CdTeCd1 − xMnxTe multiple quantum wells (MQWs) with relatively large Mn content of x ≈ 30% using the explosive single-turn coil technique. Evident features associated with the magnetic-field induced type I-type II transition were revealed in the field dependence of the heavy-hole exciton absorption for σ+ polarization — a reduction of the absorption intensity and the onset of a red-shift of the exciton energy. These observed features were found to be reproduced qualitatively well by a variational calculation when the valence-band offset ratio Qv is assumed to be 30–40%.

Dynamics of exciton relaxation and excitation transfer to donor-bound excitons in CdTe/CdMnTe quantum wells

Using time-resolved photoluminescence spectroscopy we investigate the dynamics of exciton relaxation in CdTe/Cd1−xMnxTe multiple quantum wells. Unbound excitons are photoexcited and the timescale of formation of the donor-bound excitons varies with excitation intensity from 73 ps to <8 ps and depends on movement of the unbound exciton in the well and the capture process at the donor site. Estimates of the capture cross-section of excitons by neutral donors and of the radiative recombination time of the donor-bound exciton are made. The rate of kinetic energy relaxation of a photocreated exciton from K=0 of the electron-light hole band to K=0 of the electron-heavy hole band is found to be (2.2±0.8)× 108 eV s−1.

Spin-flip Raman scattering in CdTe/Cd1-xMnxTe multiple quantum wells: A model system for the study of electron-donor binding in semiconductor heterostructures.

Spin-flip Raman scattering in CdTe/Cd1-xMnxTe multiple quantum wells: A model system for the study of electron-donor binding in semiconductor heterostructures.

Magneto-optical study of CdTe/Cd 1−TxMn xTe multiple quantum wells under high magnetic fields

The magneto-optical properties of CdTe/Cd 1−xMn xTe multiple quantum wells (MQW's) with high Mn contents of about 30% were studied through absorption measurements at high magnetic fields up to 40 T. Absorption peaks due to the heavy-hole and light-hole related excitons exhibit large Zeeman splitting. The Zeeman splitting energy of the heavy-hole excitons was compared with a variational calculation. Reduced antiferromagnetic coupling of Mn 2+ spins at the MQW heterointerface and the interdiffusion are discussed as a possible origin of the discrepancy between experiment and theory.

High-field magneto-optical study of localized excitons in CdTe/Cd 1− xMn xTe multiple quantum wells

The photoluminescence (PL) spectra of CdTe/Cd 1− x Mn x Te multiple quantum wells (MQW) were measured in pulsed magnetic fields up to 40T. The samples were grown on GaAs(1 0 0) substrates at 320°C (lower- T s sample) and 360°C (higher- T s sample) by the molecular beam epitaxy (MBE) method. In the magnetic field dependence of the PL peak positions, both red and blue shifts were observed in the low- and high-magnetic-field regions, respectively. The former is interpreted as a large Zeeman effect caused by the penetration of the exciton wavefunction of the CdTe quantum well layer into the Cd 1− x Mn x Te barrier layer. The latter is due to a diamagnetic shift of excitons in the CdTe quantum well layer. In the case of the higher- T s samples, no diamagnetic shift and anomalously large Zeeman shift were observed. These facts suggest that excitons in the quantum well layer of higher- T s samples are localized at the heterointerfaces of CdTe/Cd 1− x Mn x Te. The origin of the localization is discussed.

Growth and structure of CdTe/Cd 1− xMn xTe multiple quantum wells showing excitonic 2S states

Multiple quantum well structures of CdTe and the dilute magnetic semiconductor Cd 1−x Mn x Te(x⪅0.08) have been grown by molecular beam epitaxy on InSb substrates. High resolution double crystal X-ray diffraction analysis using rocking curve simulations based on the dynamical theory of diffraction shows that these layers are of excellent structural quality and uniformity. The diffraction data indicate the presence of a highly mismatched layer a few monolayers thick at the interface between the InSb substrate and the CdTe buffer layer, which is consistent with previous Raman spectroscopy studies identifying the phase as In 2Te 3. Photoluminescence and photoluminescence excitation spectroscopy measurements indicate that well width fluctuations occur on a monolayer scale. Observation of the 2S state of both light and heavy hole excitons allows the binding energy of both excitons to be deduced—17.1 meV and 19.7 meV respectively—considerably enhanced from their three-dimensional values.

Exciton binding energies in CdTe/Cd 1−xMn xTe multiple quantum wells

These results are compared with binding energies calculated with a variational approach which accounts for motion along the z-direction as well as in the x-y plane. The 1S and 2S states of both light hole, (e 1, ℓ 1), and heavy hole (e 1h 1) excitons have been observed in CdTe/Cd 1−xMn xTe multiple quantum wells. Clear identification of the 2S states arises from their large diamagnetic effects and their observation has allowed the light and heavy hole exciton binding energies to be investigated with changes in depth of the electron and hole confining potentials by application of a magnetic field. In a sample with x ∼ 0.75 it is found that changes of the heavy hole exciton binding energies are small, ⪅ 1 2 meV, even for large changes, ≈40 meV, of the hole confining potential. For the light hole exciton changes of the binding energy are larger, ≅ 2meV, for smaller changes, ≅ 14meV, of the hole confining potential.

Modulated Reflectance Spectroscopy of CdTe-Cd1−xMnxTe Multiple Quantum Wells and Superlattices Grown by Pulsed Laser Evaporation and Epitaxy

ABSTRACTPiezoreflectance and photoreflectance spectroscopies have been used to investigate the electronic properties of CdTe-Cd1-xMnxTe (x − 0.10) multiple quantum well and superlattice structures grown by Pulsed Laser Evaporation and Epitaxy (PLEE). The structures with the CdTe well widths from 54Å to 245Å have been investigated. The spectra exhibit a series of signatures which are attributed to free exciton transitions occuring between the heavy-hole and light-hole bands and the upper electron subbands within the CdTe well layers. The spectra indicate that the PLEE grown structures are of an excellent quality typical of the best currently available material.

Time-resolved exciton recombination in CdTe/Cd1−xMnxTe multiple quantum wells

The lifetime of excitons in CdTe/Cd1−xMnxTe multiple quantum wells at low temperature has been measured by time-resolved photoluminescence in samples of different well thickness. The excitons, which have elsewhere been shown to be localized preferentially near the heterointerfaces, possess an average lifetime which becomes shorter with decreasing well thickness and increasing external magnetic field. The results are in qualitative agreement with the expectations for a localized quasi-two-dimensional exciton with a large radiative recombination cross section.