Exciton luminescence in In 0.3Ga 0.7As/GaAs quantum well heterostructures (original) (raw)
Physical Review B, 1988
Sharp line structure associated with both the light-hole free exciton (LHFE) and heavy-hole free exciton (HHFE) in multiple-quantum-well structures of GaAs-AI"Ga& "As in photoluminescence and re6ection spectra has been deconvoluted by using photoluminescence excitation spectroscopy. A correlation is established between particular LHFE fine-structure components and specific HHFE fine-structure components. A model is developed to account for the LHFE and HHFE fine structure in these samples which exploits the nonrandom character of the observed spectra. The physical location of the excitons is demonstrated to be in regions of the well(s) with essentially identical interfacial microstructure. Evidence of difusion from effectively-narrow-well regions to wide-well regions is presented.
Interwell excitons in GaAs/AlGaAs double quantum wells and their collective properties
Journal of Experimental and Theoretical Physics, 2000
Luminescence spectra of interwell excitons in GaAs/AlGaAs double quantum wells with electricfield-tilted bands ( n -i -n ) structures were studied. In these structures the electron and the hole in the interwell exciton are spatially separated between neighboring quantum wells by a narrow AlAs barrier. Under resonant excitation by circularly polarized light the luminescence line of the interwell excitons exhibited appreciable narrowing as their concentration increased and the degree of circular polarization of the photoluminescence increased substantially. Under resonant excitation by linearly polarized light the alignment of the interwell excitons increased as a threshold process with increasing optical pumping. By analyzing time-resolved spectra and the kinetics of the photoluminescence intensity under pulsed excitation it was established that under these conditions the rate of radiative recombination increases substantially. The observed effect occurs at below-critical temperatures and is interpreted in terms of the collective behavior of the interwell excitons. Studies of the luminescence spectra in a magnetic field showed that the collective exciton phase is dielectric and in this phase the interwell excitons retain their individual properties.
Selective exciton formation in thin GaAs-AlGaAs quantum wells
Le Journal de Physique IV, 1993
We have found experimentally, that the exciton luminescence rise times in GaAdAlGaAs quantum wells oscillate as a function of incident laser energies. Guided by Monk-Carlo simulations we interpret these results as the occurrence of selective LO-phonon assisted exciton formation.
Optical investigation of biexcitons and bound excitons in GaAs quantum wells
Physical Review B, 1988
The photoluminescence spectra from a number of high-quality GaAs single-quantum-well samples grown by molecular-beam epitaxy reveal a doublet emission having an energy separation of-1.25 meV. A similar doublet was observed in a sample for which the interrupted growth technique was used. Using excitation-intensity-dependent luminescence and time-resolved spectroscopy,~e will show that the lower-energy components of these doublets have diN'erent origins in di6'erent samples and can be attributed either to biexcitons or to impurity-bound excitons. Using low-temperature photoluminescence (PL) from a number of high-quality GaAs multiple-quantum-well samples grown by molecular-beam epitaxy (MBE), Miller and co-workers'2 first reported a double peak whose splitting was-1 meV. The high-energy peak was attributed to the n 1 heavy-hole-free-exciton transition. Based on the excitation intensity, temperature, and polarization dependencies of the lower-energy peak, they concluded that this transition was due to biexcitons with a binding
Superlattices and Microstructures, 1989
The dynamics of exciton formation and decay are investigated in GaAs-AlxGal_xAS (x < 0.Is) multiquantum well structures under low excitation conditions by transient photoluminescence spectroscopy. The time resolution (10ps) is achieved by using the frequency up-conversion technique. At low temperature (T < 50 K), the luminescence is dominated by localized exciton formation and recombination processes: significant Stokes shifts from the exciton absorption line, long non-exponential rise time (ranging from 200 ps to 600 ps) and short radiative lifetime (from 200 ps to Q00 ps) are observed. At higher temperature (T > 80 K), the luminescence is dominated by free exciton radiative recombination with shorter formation time and much larger exciton lifetime (from 3 ns to 6 ns). We suggest that the exciton may trap efficiently at low temperature on interface defects, the areal density of which can be evaluated in a simple manner.
Quantum beats of type-I and type-II excitons in an InxGa1−xAs/GaAs strained single quantum well
Journal of Applied Physics, 2012
We have investigated the quantum beat of the type-I heavy-hole (HH) and the type-II light-hole (LH) excitons in an In0.15Ga0.85As/GaAs strained single quantum well (SQW) using a reflection-type pump-probe technique. The type-II LH exciton consists of the electron and LH located in the In0.15Ga0.85As and GaAs layers, respectively. The energies of the type-I and the type-II excitons were evaluated with photoreflectance spectroscopy. The exciton states were calculated based on a variational method. The time-domain signals clearly show the oscillatory structure with the period corresponding to the splitting energy of the HH and the LH excitons. From the pump-energy dependence of the Fourier transform spectrum and intensity, it is concluded that the oscillation originates from the quantum beat of the type-I HH and the type-II LH excitons.
Study of the nature of light hole excitonic transitions in InGaAs/GaAs quantum well
Vacuum, 1998
Photoreflectance (PR) spectra of strained InGaAs/GaAs MOWS were measured. Heavy and light hole excitonic transitions were observed. Applying results of theoretical calculations which include excitonic and strain effects, we obtained that the existence of type II light hole exciton in our type I MQW system should be considered.
Photoluminescence kinetics of indirect excitons inGaAs/AlxGa1−xAscoupled quantum wells
Physical Review B, 1999
Photoluminescence ͑PL͒ kinetics of long-lifetime indirect excitons in a GaAs/Al x Ga 1Ϫx As coupled quantum well characterized by a small in-plane random potential was studied at temperatures 1.5рTр15 K for a wide range of exciton densities. Strong deviations of the indirect exciton PL kinetics from monoexponential PL rise/decay were observed at low temperatures and high exciton densities. In particular, right after the excitation is switched off, the spectrally integrated indirect exciton PL intensity increased sharply. Simultaneously, the indirect exciton energy distribution was observed to narrow significantly. The observed increase in intensity is attributed to the sharp increase of occupation of the optically active exciton states. The energy distribution narrowing is explained in terms of the phonon mediated exciton energy relaxation in momentum space and in the in-plane random potential. ͓S0163-1829͑99͒00104-6͔
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1995
A specific luminescence band originating from a heterointerface ͑H band͒ has been observed in the photoluminescence spectrum ͑at 1.7 K͒ of a single GaAs/GaAlAs heterostructure. Threshold effect of epitaxial temperature on interface luminescence has been found. A model has been proposed which attributes interface luminescence to annihilation of the interface heterodimensional exciton which is composed of a two-dimensional ͑2D͒ electron ͑2D hole͒ in the notch at the interface and a three-dimensional ͑3D͒ hole ͑3D electron͒ in the GaAs bulk region near the interface. The exciton binding energy decreases when the interface ruggedness increases. In the case of large inhomogeneities ͑ruggedness of chemically abrupt interface͒ such an exciton cannot form and the corresponding H band is not observed in the spectrum. Thus, the luminescence of the interface heterodimensional exciton can serve as an indication of the interface ruggedness.
Luminescence linewidths of excitons in GaAs quantum wells below 150 K
Physical Review B, 1986
We present detailed experimental studies and a theoretical model of the linewidth as a function of temperature (& 150 K}for both heavy-hole and light-hole excitons in a GaAs-Al"Gal "As quantum well. The contributions to the linewidth of the exciton luminescence include interactions with polar optical phonons, with acoustic phonons (via deformation and piezoelectric potentials), with ionized impurities, and with Auctuations in the thickness of the well. We find that the linewidth increases subhnearly with temperature in the range 0 K to about 70 K but increases more sharply as the temperature is raised still higher.