S.-K. Chang

(100) superlattices of CdTe‐Cd0.76Mn0.24Te on (100)GaAs

This letter reports the first growth of (100) CdTe‐CdMnTe superlattices. In the past (111) superlattices of CdTe‐CdMnTe were grown on (100) GaAs substrates. To consistently achieve the desired (100) epitaxy, three different growth techniques are described. Reflection high‐energy electron diffraction is used to observe the initial nucleation of the (100) CdTe film, while transmission electron microscopy is used to investigate the nature of the interface between the epitaxial film and the substrate. The optical properties of these superlattices show interesting differences with the (111) superlattices.

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.

Excitons in CdTe/Cd1−xMnxTe multiquantum wells

Abstract We discuss results of spectroscopic studies of the optical properties of CdTe/Cd 1− x Mn x Te multiquantum wells. These structures are sources of intense luminescence at low temperatures. Dependence of luminescence spectra on temperature and external magnetic field shows strong evidence for emission by localized excitons which are attracted to the heterointerfaces.

Influence of high magnetic fields on exciton luminescence of Cd1−xMnxTe multiquantum wells

Abstract Photoluminescence from Cd1−xMnxTe multiquantum wells has been studied magnetic fields up to 21.8 Tesla. The spectra show large shifts to low energies with increasing fields. The major observations include apparent saturation of the shifts at higher fields, their anomalous temperature dependence, and a significant degree of anisotropy in the field directions parallel and perpendicular to the superlattice axis. The results support our arguments that the excitons are localized near the heterointerfaces and are substantially 2-dimensional.

Excitons and their kinetics in CdTe/(Cd, Mn)Te and ZnSe/(Zn, Mn)Se quantum wells

Abstract We show examples of recent spectroscopic studies of CdTe/(Cd, Mn)Te and ZnSe/(Zn, Mn)Se multiquantum wells (MQWs). These strained-layer structures are sources of intense excitonic luminescence at low temperatures. Dependence of luminescence spectra on temperature and the especially pronounced influence of an external magnetic field are strong evidence that the emission is dominated by localized excitons which particularly for the (111) oriented CdTe/(Cd, Mn)Te MQWs are attached to the heterointerfaces. For the (100) ZnSe/(Zn, Mn)SeMQWs the luminescence amplitude typically decreases rapidly with temperature from 2 to 100 K indicating only a weakly localized exciton. Picosecond time-resolved experiments have yielded a direct measurement of exciton energy-loss rates and lifetimes which are found to depend on quantum well width, magnetic field, and on temperature.

Quasi-two-dimensional exciton-polaron in CdTe/(Cd, Mn)Te quantum wells

Abstract The CdTe/(Cd, Mn)Te is a new superlattice system whose low temperature luminescence shows high quantum efficiency and large magnetic field induced energy shifts which imply exciton localization at the heterointerfaces in (111) oriented samples. The anisotropies and high field behavior in the exciton spectra offer important evidence for 2D character of the localized excitons. Further, the energy shifts show an anomalous temperature dependence which is not compatible with paramagnetic behavior of the Mn-ion spin system. Time-resolved luminescence experiments by picosecond laser techniqiues show how dynamical spectral shifts occur has a substantial polaron component. The main physical contribution to the polaron effects is likely to be magnetic origin, deriving from the spin exchange effects with the Mn-ions.

Resonant Raman scattering and exciton‐optical phonon coupling in CdTe/(Cd,Mn)Te quantum wells

Resonant Raman scattering at the E0 gap from longitudinal optical phonons in CdTe/(Cd,Mn)Te multiple quantum wells has been studied near the strain split n=1 exciton ground state. A large resonance enhancement is observed with distinct incoming and outgoing channels, in agreement with luminescence excitation spectra. Phonons are observed from CdTe wells and (Cd,Mn)Te barriers, indicative of small valence‐band offsets for this superlattice system. At extreme resonance, striking linewidth broadening and damping effects for the alloy phonon modes are witnessed.

Influence of heterointerfaces on optical properties of CdTe/(Cd,Mn)Te and ZnSe/(Zn,Mn)Se superlattices

A selective comparison is made of the influence of heterointerfaces on recently observed optical properties of CdTe/(Cd,Mn)Te and ZnSe/(Zn,Mn)Se superlattices in the quantum well limit. Specifically, we draw new conclusions and insight of the role of heterointerfaces on exciton localization phenomena in these strained layer structures. Amongst these II–VI superlattices, large variations are encountered which appear at least in part to be connected with interface related disorder.

Excitonic recombination at the CdTe/(Cd,Mn)Te heterointerface

We discuss results of spectroscopic studies of the optical properties of Cd1−xMnxTe multiquantum wells. These structures are sources of intense luminescence at low temperatures. Dependence of luminescence spectra on temperature and external magnetic field show strong evidence for emission by localized excitons which are attracted to the heterointerfaces.