Effects of confinement on carrier dynamics in In0.47Ga0.53As heterostructures

To study the effects of confinement by quantum-well potential discontinuities on ultrafast carrier dynamics, we performed pump-broadband probe studies of a series of In0.47Ga0.53As quantum wells excited 30 meV above the band edge. Our measurements show that the rate of carrier thermalization is well width independent; however, the rate of carrier cooling to the band edge is strongly influenced by confinement. This influence has two separate physical origins. First, the dimensionality dependence of the density of states results in a larger proportion of thermalized electrons that can emit LO phonons in three dimensions than in two. Second, modification of the phonon density of states by the ionic mass discontinuity at the well boundaries may reduce the electron - LO-phonon coupling. copyright 1998 The American Physical Society