Hot-exciton relaxation in Cd_{x}Zn_{1-x}Te/ZnTe multiple quantum wells (original) (raw)
Electro-optic exciton nonlinearities in Zn1-xCdxSe/ZnSe multiple quantum wells
Physical review. B, Condensed matter, 1996
The quantum-confined Stark effect ͑QCSE͒ in Zn 1Ϫx Cd x Se/ZnSe multiple quantum wells embedded in the intrinsic region of p-in photodiodes has been investigated by means of photoluminescence spectroscopy under applied bias and photocurrent spectroscopy. Room-temperature excitonic bleaching is observed at reverse biases as low as 3 V. Both the redshift and the reduction of the oscillator strength of the excitonic emission have been calculated by means of a variational model. We use the same model to clarify the main specific features of the QCSE in II-VI materials. ͓S0163-1829͑96͒06847-6͔
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.
Excitonic and Raman properties of ZnSe/Zn1−xCdxSe strained-layer quantum wells
Journal of Applied Physics, 1991
The optical properties of strained-layer ZnSe/Zn0.86Cd0.14Se single quantum wells have been studied. The photoluminescence under direct and indirect excitation is investigated in detail. The temperature dependence of photoluminescence and resonant Raman scattering are investigated. Very strong 2LO-phonon Raman scattering has been observed with Zn0.86Cd0.14Se quantum wells, where the scattered photon energy is in resonance with an exciton transition. Experimental exciton energies are compared with a finite-square-potential quantum-well model including band nonparabolicity and the strain effect. Based on Hill’s theory [J. Phys. C 7, 521 (1974)] we have computed the band gap of Zn1−xCdxSe as a function of composition x.
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
Radiative recombination of indirect exciton in type-II ZnSeTe/ZnSe multiple quantum wells
Journal of Luminescence, 2011
The tunability of the emission energy, oscillator strength and photoluminescence (PL) efficiency by varying the well thickness and excitation density was demonstrated in the ZnSe 0.8 Te 0.2 /ZnSe multiple quantum wells. A significant blueshift about 260 meV of the PL peak energy was observed as the well width decreased from 5 to 1 nm. An extraordinary long lifetime (300 ns) of the recombination for the widest sample was detected. The binding energy of the indirect excitons is determined as 12 meV for the thinnest sample. The reduction of PL efficiency by thermal energy is greatly suppressed by employing a high excitation power.
Applied Surface Science, 1991
The technique of resonant Rayleigh scattering is used to determine the homogeneous linewidth across the inhomogeneously broadened exciton resonance in a Cd0.25Zn0.75Te/ZnTe multiple quantum well structure. An order of magnitude increase of the Rayleigh scattering signal over background is observed on tuning a narrow-band laser through the exciton resonance at low temperatures. Spectral and temporal measurements show the effect to be a true scattering process rather than luminescence. The interface and alloy fluctuations in the quantum well give rise to spatial fluctuations in the dielectric response of the system while the large exciton resonance causes strong enhancement of scattering. The homogeneous linewidth was calculated across the exciton resonance. The technique is compared with the dephasing and hole-burning techniques more commonly used in homogeneous linewidth measurements.
Coherent phenomena and interaction of excitons in wide ZnSe/Zn1–xMgxSe single quantum wells
Journal of Crystal Growth, 1998
We investigate the transient four-wave mixing (FWM) response of wide ZnSe/Zn, -XMg,Se single quantum wells in a two-beam self-diffraction configuration. The spectrally resolved FWM signals show excitonic transitions which are essentially homogeneously broadened, and show dephasing times between 1 and 2 ps at a lattice temperature of 10 K. Simultaneous excitation of several exciton states leads to pronounced quantum beats in the FWM signal. The formation of heavy-hole biexcitons with binding energies of E bXX = 3.5 f 0.5 meV is identified by polarization-dependent measurements. These measurements also indicate that excitation-induced dephasing gives the main contribution to the FWM process. 0
Charged excitons trapped on monomolecular CdTe islands in wide ZnTe-(Zn,Mg)Te quantum wells
Physical Review B, 1998
Optical spectroscopy at Tϭ2 K reveals systematically a low-energy companion to the features of heavy-and light-hole excitons localized on CdTe 1-ML-high islands, buried in wide ZnTe/͑Zn,Mg͒ Te quantum wells. These transitions are assigned to a negatively charged excitonic complex ͑trion͒ from magnetoreflectance and photoluminescence results. A mechanism of formation of the trion is proposed. A clear correlation is found between the exciton energies, which depend on the size and strain of the islands, and the trion binding energy, which varies between 1 and 3 meV. ͓S0163-1829͑98͒02248-6͔
Acta Physica Polonica A, 2009
Systematic studies of neutral heavy-hole excitonic line energy changes in a strong excitation regime were carried out by means of a pump-probe method for quantum wells containing a 2D gas of free holes. Energy shift of X e1hh1 line was analyzed for different excitation energies at fixed delay between pump and probe pulses, also under external magnetic field. It was observed that this shift depends not only on the density of created excitons but also directly on the pump energy. In co-polarization configuration for excitation energy below an absorption resonance the energetic blue shift rises linearly with the elevated exciton density (localized excitons are created). For energies slightly above the resonance, the blue shift diminishes dramatically in spite of high exciton density present (delocalized excitons are created). Model absorption calculations are in qualitative agreement with the experimental data.
Metastable excitons inZnSe/Zn1−xFexSequantum wells
Physical Review B, 1997
We present an optical ͑reflectance and photoluminescence͒ study of metastable excitons in ZnSe/Zn 1Ϫx Fe x Se quantum-well structures. These states are associated with the type-II (Ϫ 1 2 , Ϫ 3 2) groundstate exciton of the system. The metastable excitons are formed because the Coulomb attraction of the m j ϭ Ϫ 1 2 electron tends to localize the m j ϭϪ 3 2 hole in the vicinity of the electron. This complex breaks apart as the temperature increases, and the system returns to its ground state in which the m j ϭϪ 1 2 electron and the m j ϭϪ 3 2 hole are segregated. ͓S0163-1829͑97͒02635-0͔