Suppression of surface-related loss in a gated semiconductor microcavity

TL;DR

This paper demonstrates a surface passivation technique that significantly reduces surface-related optical losses in a miniaturized GaAs microcavity, enhancing its performance for nano-photonic applications.

Contribution

The authors introduce a novel surface passivation method that nearly eliminates surface-related losses in a GaAs microcavity, improving its optical quality and potential for integrated photonics.

Findings

Surface passivation reduces losses by nearly two orders of magnitude.

Passivation eliminates surface electric fields, reducing below-bandgap absorption.

Surface passivation also decreases scattering at the GaAs surface.

Abstract

We present a surface passivation method that reduces surface-related losses by almost two orders of magnitude in a highly miniaturized GaAs open microcavity. The microcavity consists of a curved dielectric distributed Bragg reflector (DBR) with radius $\sim 10$ $\mu$m paired with a GaAs-based heterostructure. The heterostructure consists of a semiconductor DBR followed by an n-i-p diode with a layer of quantum dots in the intrinsic region. Free-carrier absorption in the highly doped n- and p-layers is minimized by positioning them close to a node of the vacuum electromagnetic-field. The surface, however, resides at an anti-node of the vacuum field and results in significant loss. These losses are much reduced by surface passivation. The strong dependence on wavelength implies that the main effect of the surface passivation is to eliminate the surface electric field, thereby quenching below-bandgap absorption via a Franz-Keldysh-like effect. An additional benefit is that the surface passivation reduces scattering at the GaAs surface. These results are important in other nano-photonic devices which rely on a GaAs-vacuum interface to confine the electromagnetic field.