Absorption And Refraction Spectroscopy Of A Tunable-Electron- Density Quantum Well/Reservoir.

We present differential absorption and refraction spectroscopy of a novel InGaAs/InAlAs multiple quantum well heterostructure in which the electron density inside the well is controlled electrically. This is achieved by providing a reservoir of electrons close to each quantum well in every fundamental building block. By applying a bias to the structure electrons can be transferred from this reservoir into the nearby quantum well where they quench the absorption due to the Pauli-exclusion principle. Our electroabsorption spectra reveal information about the Fermi-energies in the quantum well and the reservoir as well as the electric fields in the well and the barrier material. In addition, we find that quenching of the quantum well absorption is accompanied by a large change in refractive index below the quantum well absorption edge, which is proportional to the number of electrons in the well. We demonstrate on a set of samples that the structure can be quantum mechanically engineered.