Picosecond time evolution of free electron-hole pairs into excitons in GaAs quantum wells (original) (raw)
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physica status solidi (c), 2005
We present the results of a detailed time resolved luminescence study carried on a very high quality In-GaAs quantum well sample. We clearly separate the contributions to the total intensity at the energy of the exciton and at the band by performing experiments with the proper spectral resolution and sensitivity, allowing to keep the observation of these two separate contributions over a broad range of times and densities. This enables us to access to the exciton formation rate over a broad range of pair densities. We also evidence the dominant contribution of excitons to the luminescence signal even when their population is small, and the absence of thermal equilibrium between excitons and free carriers at low enough densities.
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.
Picosecond photoluminescence of resonantly-excited excitons in GaAs quantum wells
Le Journal de Physique IV, 1993
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Extended Abstracts of the 1993 International Conference on Solid State Devices and Materials, 1993
We present the detailed analyses of temporal profiles of photoluminescence from heavy-hole excitons in AlGaAs/GaAs quantum wells. We have observed the two-component exponential decay when the excitation density is low. We have confirmed by measuring the lateral spatial motion of excitons that the fast component is attributed to radiative recombinations of free excitons while the slowly decaying component is due to localized excitons. To the best of our knowledge, this is the first direct observation of localization of 2-dimensional excitons in quantum wells.
Physical Review B, 1988
Two-dimensional excitons in GaAs/Al"Ga& "As single quantum wells exposed to electric fields perpendicular to the layers are studied by means of time-resolved photoluminescence. The temporal decay of the excitonic emission distinguishes two characteristic field regimes: In the smallfield regime, luminescence lifetime increases with increasing field, and a pronounced Stark shift is additionally observed. In the high-field domain)50 kV/cm, the lifetime decreases with increasing field because of excitonic field ionization, leading to carrier tunneling through the barriers. We discuss these features within the framework of a simple semiclassical model. Quantitative agreement is obtained for quantum wells of different well widths and barrier thicknesses with respect to lifetime, luminescence intensity, and tunneling current. Thus a consistent description of the dynamics of two-dimensional excitons exposed to an electric field is obtained.
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
Charged exciton dynamics in GaAs quantum wells
1998
We study the dynamics of the charged and neutral excitons in a modulation-doped GaAs quantum well by time-resolved photoluminescence under a resonant excitation. The radiative lifetime of the charged exciton is found to be surprisingly short, 60 ps. This time is temperature independent between 2 and 10 K, and increases by a factor of 2 at 6 T. We discuss our findings in view of present theories of exciton radiative decay. S0163-18299803143-9
physica status solidi (c), 2004
We report on a detailed study of the photoluminescence (PL) in high quality GaAs/AlGaAs quantum wells containing a two-dimensional electron gas. The 2DEG density was varied by optical depletion (with He-Ne laser illumination) in the range of n 2D = (7-3) × 10 10 cm -2 . The n 2D -dependent PL spectra were studied under a perpendicularly applied magnetic field B < 12 T at T L = 0.3 and 1.5 K. The evolution from free hole-2DEG to charged exciton PL with decreasing n 2D or with increasing magnetic field is attributed to the appearance of regions containing localized electrons as the filling factor decreases below ν = 0.4-0.3. This results in simultaneous PL of the free hole-2DEG originating from electron puddles and of charged exciton from regions with localized electrons.
Determination of the exciton formation in quantum wells from time-resolved interband luminescence
2004
We present the results of a detailed time-resolved luminescence study carried out on a very high quality InGaAs quantum well sample where the contributions at the energy of the exciton and at the band edge can be clearly separated. We perform this experiment with a spectral resolution and a sensitivity of the setup, allowing us to keep the observation of these two separate contributions over a broad range of times and densities.
Kinetics of the inner ring in the exciton emission pattern in coupled GaAs quantum wells
Physical Review B, 2009
We report on the kinetics of the inner ring in the exciton emission pattern. The formation time of the inner ring following the onset of the laser excitation is found to be about 30 ns. The inner ring is also found to disappear within 4 ns after the laser termination. The latter process is accompanied by a jump in the photoluminescence ͑PL͒ intensity. The spatial dependence of the PL jump indicates that the excitons outside of the region of laser excitation, including the inner ring region, are efficiently cooled to the lattice temperature even during the laser excitation. The ring formation and disappearance are explained in terms of exciton transport and cooling.