Dynamics of an Optically Generated Electric Field in a Quantum Dot Molecule Device Using Time-Resolved Photoluminescence Measurements

Abstract

Interdot transitions in the emission spectra of a quantum dot molecule may be used as a sensitive nanoscale probe to measure electric fields. Here, we demonstrate this potential by monitoring the temporal behavior of photovoltaic band flattening in a Schottky diode structure using a two-color excitation scheme. First, a continuous wave laser is tuned to an excitation energy below the wetting layer (WL) emission energy to create the interdot transition that is used to monitor the electric field in the device. A second modulated laser, at higher energy, is then used to create the optically generated electric field (OGEF) which leads to the photovoltaic band flattening. It is found that the rise time of this OGEF is ∼2.85 μs and the decay, or fall time, is on the order of ∼110 μs, most likely determined by device-dependent carrier transport, trapping, and tunneling rates. We also find that, at higher applied fields, the OGEF tends to decay faster and the measured values are consistent with the photovoltaic band-flattening effects reported previously in nanostructure devices.