The nonradiative recombination effect on the photoluminescence (PL) decay dynamics in GaInNAs/GaAs quantum wells is studied by photoluminescence and time-resolved photoluminescence under various excitation intensities and temperatures. It is found that the PL decay dynamics strongly depends on the excitation intensity. In particular, under the moderate excitation levels the PL decay curves exhibit unusual non-exponential behavior and show a convex shape. By introducing a new concept of the effective concentration of nonradiative recombination centers into a rate equation, the observed results are well simulated. In the cw PL measurement, a rapid PL quenching is observed even at very low temperature and is of the excitation power dependence. These results further demonstrate that the non-radiative recombination process plays a very important role on the optical properties of GaInNAs/GaAs quantum wells.
The high energy tails in continuous wave photoluminescence spectra of asymmetric coupled double wells are studied under various excitation intensities and at different lattice temperatures. Hole mixing tunneling induced thermal population of hot carriers is firstly demonstrated and distinguished from photon heating. The corresponding thermalization process is shown to be dominated by acoustic phonon scattering.
Photoluminescence (PL) and time-resolved PL measurements were used to study the exciton recombination processes in GaAs/AlGaAs, InGaAs/GaAs, and InGaAs/AlGaAs quantum wells (QWs). An increasing lifetime with decreasing well width has been observed in very narrow and high quality GaAs/AlGaAs samples, and attributed to the reduced overlap of the electron and hole wave functions and the increase of the exciton effective volume. In InGaAs/GaAs strained QWs the measured exciton lifetimes were found to be of In composition dependence: the more the indium composition, the shorter the lifetime. The mechanisms, including the random alloy disordering and the degeneration of quasi two-dimensional properties of excitons were inferred to explain the experimental results. The nonradiative recombination was stressed in our InGaAs/AlGaAs QWs. A combined analysis of cw PL and time-resolved PL measurements allows us to separate the radiative and nonradiative decay times in our sample. The observed dominant nonradiative recombination has been tentatively ascribed to the poor quality of AlGaAs.
A modified coherent model, which includes the inhomogeneous broadening effect of the excitonic linewidth, of the resonant tunneling (RT) of electrons in double quantum wells is presented. The validity of the model is confirmed with the experiments and shows that the resonant tunneling process of electrons can be mostly explained by the simple coherent theory. We discuss the influence of linewidth on resonant tunneling time, which is strongly dependent on the barrier thickness LB, by introducing the contrast-ratio (Lambda) and the full width at half depth (FWHD) of the RT valley, and we found that (Lambda) first increases with increasing barrier thickness, reaches a maximum, and then decreases with a further increase of LB, in striking contrast to the Fabry-Perot (FP) analogy where a monotonous increase of the current peak-to-valley ratio is predicted. A decrease of the FWHD monotonously with increase of LB is also found. We discuss the potential application of our results in the design of tunneling devices.
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