Inter-subband scattering and thermalization of electrons in quantum wells studied with mid-infrared femtosecond pulses

Abstract

The dynamics of carriers in two-dimensional semiconductor structures is governed by both intra- and inter-subband scattering processes dominantly due to carrier-carrier and carrier-phonon interactions. In the case of subband separations larger than the LO-phonon energy a broad range of lifetimes of n=2 carriers between 150 fs [1], 1 ps [2], and 15 ps [3] was reported. In addition, there is only poor information about thermalization of two-dimensional carrier gases. Using femtosecond light pulses in the mid-infrared spectral range allows the direct selective observation of electron or hole dynamics in quantum wells [4], In this paper, we study the inter- and intra-subband relaxation of electrons in n-type modulation-doped GalnAs/AlInAs multiple quantum wells (MQWs). Our experiments provide new information on the n=2 lifetime and give the first direct insight into electron therm- alization after inter-subband excitation.