Measurement of the interwell carrier transport lifetime in multiquantum-well optical amplifiers by polarization-resolved four-wave mixing

Abstract

Polarization-resolved four-wave mixing spectroscopy is used to study interwell carrier dynamics in an alternating-strain multiquantum-well optical amplifier. The experimental data are found to be in good agreement with a simple model based on quantum capture/escape and diffusion processes. The results suggest that the interwell transport in this structure is mainly limited by carrier escape, and give an estimate of 16 ps for the overall transport lifetime. © 1996 American Institute of Physics. ͓S0003-6951͑96͒04753-5͔Interwell carrier transport in semiconductor multiquantum-well structures is a highly nonlinear process with significant implications to the use of these structures in electrical and optical devices. Of particular interest is the finite rate at which the carrier densities in neighboring wells reach equilibrium with one another and with the distribution of unconfined carriers in the barrier region. This process has received considerable attention in recent years 1-8 since it has been associated with nonlinear gain compression, and hence the maximum modulation bandwidth of quantum-well lasers.In this letter, we report on a simple experiment aimed at measuring the rate at which modulated carrier distributions are transferred between neighboring quantum wells. This measurement is based on polarization-resolved four-wave mixing ͑FWM͒ spectroscopy in an InGaAsP alternatingstrain semiconductor optical amplifier ͑SOA͒, consisting of three pairs of tensile and compressively strained quantum wells.9 In a recent article 7 it was shown how this technique enables selective excitation and probing of adjacent quantum wells, and the effect of interwell transport was qualitatively observed. Here we apply the results of a subsequent detailed study of the polarization properties of FWM 10 to also obtain quantitative information. In particular, a fit of the experimental data to a simple model gives an estimated 16 ps for the interwell transport lifetime in the structure measured.

Four-wave mixing mediated by the capture of electrons and holes in semiconductor quantum-well laser amplifiers

“…2, we immediately obtain an electronic capture lifetime of 1.8 psec. Incidentally, this estimate is consistent with a recent measurement of the interwell transport rate in the same SOA, 10 from which a value of 1.5 psec for cap ͑and 8 psec for esc ) was inferred.…”

“…so that on the basis of this simple model we expect the FWM conversion efficiency to exhibit one pole at 1/ s and another at 1/ cap ϩ1/ esc ϩ1/ s (Ϸ1/ cap since in general the capture lifetime is shorter than both the stimulated recombination and the escape lifetimes 5,10 ͒. As a result, cap can be directly read off the experimental data, provided that the frequency dependence is entirely ascribed to the carrier-density modulation response described by Eq.…”

“…[9][10][11][12] In this letter, we present a novel experimental technique based on frequency-resolved FWM to directly study capture processes in ͑multi͒quantum-well semiconductor optical amplifiers ͑SOAs͒. In the experiment, a small-signal carrier density modulation is generated in the electronic states near the barrier band-edges ͑by photomixing of two pump waves͒, and is then probed in the quantum wells as a function of the modulation frequency.…”

Quantum-well capture and interwell transport in semiconductor active layers

“…intrinsic capture. In the following section, we will describe how this limitation can be overcome by generating the modulation via photomixing of two nondegenerate waves, and we will then describe two applications of this technique [25,26].…”

“…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.…”