CAPTURE OF PHOTOEXCITED CARRIERS IN A SINGLE QUANTUM-WELL WITH DIFFERENT CONFINEMENT STRUCTURES

We report experimental and theoretical studies of photoexcited carrier trapping in a GaAs-Al(x)Ga1-xAs single quantum well with three different typical confinement layer structures: standard separate-confinement heterostructure (SCH) or graded SCH (GRIN-SCH, linearly graded LGRIN-SCH, or parabolically graded PGRIN-SCH). The capture is studied by means of time-resolved luminescence with 600 fs resolution. Measurements, performed from 20 to 300 K, show an appreciably shorter trapping time in the GRIN-SCH (2 ps at 80 K to 8 ps at 300 K) than in the SCH (between 22 and 14 ps in the same temperature range). Experimental results are fitted by a one-dimensional "drift-diffusion" model, and the mobility of holes is deduced from the calculations. We evidence a short but finite capture time at the edge of the well. The diffusion process is limited by holes in the direct region of the alloy and by both particles in the indirect part of the confinement layer.