Electroabsorption in gated GaAs nanophotonic waveguides

TL;DR

This paper investigates electroabsorption in GaAs nanophotonic waveguides with embedded p-i-n junctions, analyzing loss mechanisms and their dependence on electric field, wavelength, and temperature to inform quantum photonic device development.

Contribution

It provides a detailed analysis of electroabsorption in GaAs waveguides, extending the Franz-Keldysh model and identifying residual absorption effects relevant for quantum photonics.

Findings

Electroabsorption extends over 200 meV below GaAs bandgap.

Residual absorption causes over 20 dB/mm loss at room temperature.

Loss mechanisms are influenced by Fermi-level pinning at the surface.

Abstract

We report on the analysis of electroabsorption in thin GaAs/Al$_{0.3}$Ga$_{0.7}$As nanophotonic waveguides with an embedded $p$-$i$-$n$ junction. By measuring the transmission through waveguides of different lengths, we derive the propagation loss as a function of electric field, wavelength, and temperature. The results are in good agreement with the Franz-Keldysh model of electroabsorption extending over 200 meV below the GaAs bandgap, i.e. in the 910--970 nm wavelength range. We find a pronounced residual absorption in forward bias, which we attribute to Fermi-level pinning at the waveguide surface, producing over 20 dB/mm loss at room temperature. These results are essential for understanding the origin of loss in nanophotonic devices operating in the emission range of self-assembled InAs semiconductor quantum dots, towards the realization of scalable quantum photonic integrated circuits.