The capture time for an electron in a graded index separate confinemen
t heterostructure (GRINSCH) is calculated as a function of quantum-wel
l width. The electron's interactions with the other electrons in the w
ell along with the phonons are included in the random-phase approximat
ion using full multiple-subband and frequency-dependent screening. It
is shown that at sufficiently high electron densities, there is a sign
ificant increase of the capture rate with electron density except for
quantum-well widths near a phonon resonance.