Experimental and Theoretical Study of Polarization-dependent Optical Transitions from InAs Quantum Dots at Telecommunication-Wavelengths (1.3-1.5{\mu}m)

TL;DR

This study combines experimental and theoretical methods to analyze how polarization-dependent optical transitions in InAs quantum dots can be modified for telecommunication wavelengths, focusing on stacked QD layers and their polarization responses.

Contribution

It provides new insights into polarization behavior of stacked quantum dot layers and demonstrates how stacking and capping layers influence emission wavelength and polarization response.

Findings

Stacked QD layers show altered TE/TM polarization ratios.

InGaAs capping increases TE/TM ratio in two-layer stacks.

Experimental and atomistic modeling results are consistent.

Abstract

The design of some optical devices such as semiconductor optical amplifiers for telecommunication applications requires polarization-insensitive optical emission at the long wavelengths (1300-1550 nm). Self-assembled InAs/GaAs quantum dots (QDs) typically exhibit ground state optical emission at wavelengths shorter than 1300 nm with highly polarization-sensitive characteristics, although this can be modified by using low growth rates, the incorporation of strain-reducing capping layers or growth of closely-stacked QD layers. Exploiting the strain interactions between closely stacked QD layers also allows greater freedom in the choice of growth conditions for the upper layers, so that both a significant extension in their emission wavelength and an improved polarization response can be achieved due to modification of the QD size, strain and composition. In this paper we investigate the polarization behavior of single and stacked QD layers using room temperature sub-lasing-threshold electroluminescence and photovoltage measurements as well as atomistic modeling with the NEMO 3-D simulator. A reduction is observed in the ratio of the transverse electric (TE) to transverse magnetic (TM) optical mode response for a GaAs-capped QD stack compared to a single QD layer, but when the second layer of the two-layer stack is InGaAs-capped an increase in the TE/TM ratio is observed, in contrast to recent reports for single QD layers.