Exciton dynamics in Cd0.33Zn0.67Te/ZnTe single quantum wells (original) (raw)
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Quantum-confined Stark effect on spatially indirect excitons in CdTe/CdxZn1−xTe quantum wells
Physical Review B, 1997
The quantum-confined Stark effect is studied in the mixed type-I/type-II CdTe/Cd x Zn 1Ϫx Te strained heterostructures. The type-II nature of the light-hole excitons is unambiguously confirmed by the blueshift observed under increasing electric field, in good agreement with calculations. On the other hand, the heavy-hole excitons are redshifted as expected for type-I excitons. The peculiar valence-band alignment, resulting from the sign reversal of the strain between the wells and the barriers, is used to detect the electric-field induced mixing of LH 1 and HH 2 confined hole states. An accurate value for the long-disputed chemical valence-band offset of CdTe/ZnTe system is extracted as ⌬E V ϭ(11Ϯ3)% of the band-gap difference between unstrained CdTe and ZnTe materials. ͓S0163-1829͑96͒06835-X͔
Surface Review and Letters, 2002
Layers of 6 and 16 Cd-Te-Zn-Te periods were grown by atomic layer epitaxy (ALE) within ZnTe thin films. Different samples were grown at substrate temperatures of 260 and 290°C. Information about the kinetics of growth and surface reconstruction during the ALE growth of CdTe and ZnTe films, and Cd-Te-Zn-Te periods was obtained by means of reflection high-energy electron diffraction (RHEED) experiments and through the analysis of the temporal behavior of the intensities of several features of the RHEED patterns. The photoluminescence of the sample grown at 260°C presents two narrow and intense peaks corresponding to emission from quantum wells (QWs). However, the spectrum of the samples grown at 290°C does not show any feature associated with QWs, the spectrum resembling that of a ZnTe film. Cd replacement by Zn atoms explains the absence of the CdZnTe QWs at 290°C and a lower Cd content than expected at 260°C. The replacement of Cd atoms by Zn atoms in the CdTe surface was clearly demonstrated by Auger experiments.
Excitons as a probe of interface morphology in Cd(Zn)Se/ZnSe heterostructures
Applied Surface Science, 2000
. We present studies of the excitonic spectrum in superlattices SLs of CdSe insertions in a ZnSe matrix aimed at elucidating the CdSerZnSe interface morphology. The experimental photoluminescence excitation spectra are compared with the results of variational exciton calculations performed within the effective mass approximation. The shape of the Ž . average vertical along the SL growth axis distribution of CdSe within each insertion, used in the calculations, was obtained Ž . from a theoretical simulation of X-ray diffraction XRD rocking curves measured in the same samples. The results indicate Ž . that the thinnest layers are graded composition ZnCdSe quantum wells QWs , generally homogeneous in the layer planes, Ž . whereas flat islands enriched by Cd appear at the CdSe nominal thickness larger than 0.5-0.6 monolayer ML . q
Relaxation of excitons in coherently strained CdTe/ZnTe quantum wells
Physical Review B, 1991
The relaxation kinetics of photogenerated excitons have been investigated in coherently strained CdTe/ZnTe quantum wells. Picosecond time-resolved luminescence spectra clearly display several replicas of the excitation pump due to the relaxation of photogenerated excitons in the CdTe well assisted by the emission of optical phonons. The luminescence replicas merge into a single broadband at a time typically larger than 300 ps, revealing spatial diAusion of excitons in the well. We study the gradual localization of photogenerated excitons from the decay of the hot luminescence.
Optical properties versus growth conditions of CdTe submonolayers inserted in ZnTe quantum wells
Physical Review B, 1998
Standard and piezomodulated optical spectroscopy is performed on ZnTe quantum wells embedding integer and fractional monolayers of CdTe. The samples, grown in a molecular-beam-epitaxy setup on the ͑001͒ surface of ZnTe substrates, all basically consist of 120-ML-wide ZnTe/͑Zn,Mg͒Te quantum wells, and some of them contain five equally spaced full or half-monolayers of CdTe, producing monomolecular islands of CdTe ''buried'' in the wide host ZnTe well. The latter behave as efficient recombination centers for excitons. In order to change the size and the configuration of the islands, various growth parameters have been changed between the different samples, e.g., the growth process ͑molecular-beam epitaxy of binaries or ternaries, or atomic-layer epitaxy͒ or the temperature. From spectroscopic measurements, the influence of these parameters is analyzed in detail, in terms of the size of the islands and of their in-plane spacing, or of the vertical correlation between these islands. The internal strain state of the CdTe insertions and the overall photoluminescence efficiency are also studied versus growth conditions. ͓S0163-1829͑98͒01047-9͔
Optical spectroscopy of single Cd0.6Zn0.4Te/ZnTe quantum dots on Si substrate
Thin Solid Films, 2011
a b s t r a c t Keywords: Cadmium zinc telluride II-VI compound semiconductors Quantum dots Si substrate Single dot spectroscopy Photoluminescence Molecular beam epitaxy Microphotoluminescence (μ-PL) measurements were carried out to investigate the optical properties of single Cd 0.6 Zn 0.4 Te/ZnTe quantum dots (QDs) grown on Si substrate by using molecular beam epitaxy. The high quality of single Cd 0.6 Zn 0.4 Te/ZnTe QDs is witnessed by resolution-limited emission, negligible background and absence of measurable spectral jitter or blinking. Polarization-dependent and powerdependent μ-PL spectroscopy measurements were performed to identify the exciton, the biexciton, and the charged exciton in the emission spectra of single QDs. Furthermore a weak linearly polarized line is observed on the low energy side of the neutral exciton and is ascribed to dark exciton recombination.
Journal of Applied Physics, 2006
By controlled annealing of small ZnSe mesas with embedded CdZnSe quantum dots ͑QDs͒ at considerably low temperatures, significant changes of the QD luminescence have been observed. To investigate the spectral evolution of single exciton lines several thermal annealing steps were performed successively, and large energy shifts of single exciton ͑X͒ lines due to annealing were traced. In annealed QDs the biexciton ͑XX͒ emission is drastically enhanced. Biexciton binding energies less than 10 meV were recorded for the thermally annealed CdZnSe QDs, indicating a considerable change in the QD confinement. The pronounced energy shifts of the QD luminescence is attributed to the Cd-Zn interdiffusion between the CdZnSe QDs and the surrounding ZnSe matrix. In small mesas interdiffusion activation energy ͑E A ͒ of less than 1 eV was determined. This value of E A is half of that recorded for the Cd-Zn interdiffusion in large QD ensembles, indicating that the sidewalls of the etched mesas play an important role in the observed diffusion process.
Spectroscopy of donors and donor-bound excitons in CdTe/Cd1−xZnxTe multiple quantum wells
Materials Science and Engineering: B, 1993
Optical spectra for D°X (excitons bound by neutral donors) are identified in emission and absorption spectra of CdTe/ Cdl-xZnxTe multiple quantum wells that were planar-doped with indium. The effect of quantum confinement on the exciton localization energy is measured as a function of well width. The ls-' 2p + transition of neutral donors is studied by faroIR magnetoabsorption spectroscopy and shows no evidence for segregation of the dopant atoms.
Effect of structural imperfections on luminescence of ZnCdSe/ZnSe quantum wells
Journal of Alloys and Compounds, 2004
The structural and luminescence properties of Zn 1−x Cd x Se/ZnSe multi-quantum well (MQW) structures with high molar fraction of cadmium (30-50%) and wide ZnSe barriers (50, 100 and 500 nm) grown by molecular beam epitaxy (MBE) have been investigated by high-resolution X-ray diffraction (HRXRD) and photoluminescence (PL) methods. It is shown that the fluctuations of composition within the quantum well layer determine the full-width at half maximum (FWHM) of the QW photoluminescence peak. The unusual polarization characteristics of this photoluminescence have been observed. The emission peak in the edge geometry is strongly polarized perpendicularly to the QW plane. This effect is ascribed to the localization of the ground-state heavy-hole-like excitons in the regions with increased cadmium content.