High-resolution spectroscopy of defect-bound excitons and acceptors in GaAs grown by molecular-beam epitaxy

Revealing and Characterizing Dark Excitons through Coherent Multidimensional Spectroscopy

Dark excitons are of fundamental importance in a broad range of contexts but are difficult to study using conventional optical spectroscopy due to their weak interaction with light. We show how coherent multidimensional spectroscopy can reveal and characterize dark states. Using this approach, we identify parity-forbidden and spatially indirect excitons in InGaAs/GaAs quantum wells and determine details regarding lifetimes, homogeneous and inhomogeneous linewidths, broadening mechanisms, and coupling strengths. The observations of coherent coupling between these states and bright excitons hint at a role for a multistep process by which excitons in the barrier can relax into the quantum wells.

Optical spectroscopy of single impurity centers in semiconductors

Using optical spectroscopy with diffraction limited spatial resolution, the possibility of measuring the luminescence from single impurity centers in a semiconductor is demonstrated. Selectively studying individual centers that are formed by two neighboring nitrogen atoms in GaAs makes it possible to unveil their otherwise concealed polarization anisotropy, analyze their selection rules, identify their particular configuration, map their spatial distribution, and demonstrate the presence of a diversity of local environments. Circumventing the limitation imposed by ensemble averaging and the ability to discriminate the individual electronic responses from discrete emitters provides an unprecedented perspective on the nanoscience of impurities.