Dynamics of carrier transport and carrier capture inIn1−xGa

Abstract

We investigate the carrier-transfer dynamics in In& Ga As/Inp heterostructures using luminescence upconversion spectroscopy with 300-fs time resolution. Carrier transport across the InP barriers to the quantum wells and the final carrier capture into confined states of the quantum wells are separated in a comparative study of samples of different well and barrier thicknesses. The transport of carriers across the barrier material to the quantum wells is found to be almost instantaneous for barrier thicknesses up to 30 nm. We obtain capture-time constants of about 800 fs for electrons and 200 S for holes. The capture times are virtually independent of well width. We develop a formalism to calculate the carrier transfer time from the barriers to the quantum wells for given well and barrier thicknesses. An upper limit of modulation frequencies set by this transfer process of the order of 300 GHz for devices with thin barriers is derived.

Quantum-well capture and interwell transport in semiconductor active layers

“…On the other hand, it has been pointed out [20] that at high carrier densities carrier-carrier scattering causes a large lifetime broadening, and hence a strong reduction in the coherence length of the unbound carriers, so that they behave more like semiclassical wavepackets. Therefore, in this regime quantum effects such as the well width oscillations are expected to be washed out; some experimental results [17,20], performed under conditions comparable with those of laser operation, seem to confirm these arguments.…”

“…at different temperatures, carrier densities, well and barrier widths, etc). These include static [10,11,38] and time-resolved [7,[12][13][14][15][16][17][18][19] photoluminescence, pump-probe spectroscopy [20][21][22] and modulation response measurements [23][24][25][26]. The estimated values for the capture lifetime reported in these works vary over a wide range, from several hundreds of femtoseconds to several tens of picoseconds, which is only partly justified by the differences among the samples studied.…”

“…A remarkable result of these early studies was the prediction of an oscillatory dependence of the capture rate on the QW width. The large body of experimental work that followed [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26], based on several different techniques, found measured values for the capture lifetime varying over a wide range, from a fraction to tens of picoseconds, depending on the experimental conditions. Similarly, the predicted oscillations with well width were only observed under appropriate conditions [10,18,21], most notably in the low carrier density regime, where the lifetime broadening of the delocalized single-particle states is small.…”

Electron relaxation and capture in InGaAsP quantum well laser structures

“…6 The same effect has been previously observed for the InGaAs/InP QW structures. 7 Carrier heating in the barriers by the capture process is a possible explanation for these experimental findings.…”

“…It should be noted that the obtained value corresponds to the local capture time in the state space, since in the multiple QW structures used in this experiment the barriers are thin enough for the carrier transport in the barriers to be neglected. 7 Carrier transport in confinement layers should not have much influence on the measured capture times too, because, for the excitation intensity used, the density of electrons generated in the vicinity of the QWs is sufficient to fill the wells. 4 Then, the carriers arriving from the confinement layers would be blocked from being captured into the QWs during the time scale of interest and would not affect PL transients at the energies corresponding to the QW transitions.…”