Dynamics of carrier transport and carrier capture in ${\mathrm{In}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ga}}_{\mathit{x}}$As/InP heterostructures

We investigate the carrier-transfer dynamics in ${\mathrm{In}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Ga}}_{\mathit{x}}$As/InP heterostructures using luminescence upconversion spectroscopy with 300-fs time resolution. Carrier transport across the InP barriers to the quantum wells and the final carrier capture into confined states of the quantum wells are separated in a comparative study of samples of different well and barrier thicknesses. The transport of carriers across the barrier material to the quantum wells is found to be almost instantaneous for barrier thicknesses up to 30 nm. We obtain capture-time constants of about 800 fs for electrons and 200 fs for holes. The capture times are virtually independent of well width. We develop a formalism to calculate the carrier transfer time from the barriers to the quantum wells for given well and barrier thicknesses. An upper limit of modulation frequencies set by this transfer process of the order of 300 GHz for devices with thin barriers is derived.