Atypical dependence of excited exciton energy levels and electron-hole correlation on emission energy in pyramidal InP-based quantum dots

Michał Gawełczyk

doi:10.1038/s41598-021-04084-z

Abstract

We calculate the spectrum of excited exciton states in application-relevant self-assembled pyramidal quantum dots grown in InAs/InP and InAs/AlGaInAs material systems. These types of dots have been recently shown to combine the emission in the third optical fiber window with low surface density and a reasonable level of in-plane symmetry of emitters, which predestines them for studies on single- and entangled-photon emission and for corresponding applications. The spectrum of optically active excited states is crucial for successful resonant and quasi-resonant excitation of emitters, allowing for conservation of angular momentum and addressing individual selected quantum states. Here, we show that in both types of studied dots, due to their specific morphology of truncated pyramid, the density of excited-state ladder, especially the s–p shell splitting may follow an unconventional dependence on emission energy, opposite to the one typically met in regular quantum dots. We obtain this result via modeling based on available morphological data and calculation within the multi-band {{varvec{k}} {cdot } {varvec{p}}} envelope-function theory combined with the configuration-interaction method used to calculate exciton states. Then, we explain this observation in purely geometric terms, as a result of an increasing effective quantum confinement width in a pyramid that is progressively cut from the top. Additionally, we show that the inverted trend is also manifested in the amount of electron-hole correlation in the exciton ground state, which also shows an anomalous dependence on emission energy and quantum dot volume.

Highlights

Semiconductor quantum dots (QDs) are constantly attracting attention in various research fields, but the aspects on which the strongest emphasis is placed change from a decade to a decade
While various pairs of semiconductor materials have been used to fabricate QDs, recently, there has been a dynamic development of such technology for InAs embedded in matrices of InP-based alloys, namely various zincblende III–V semiconductor alloys that are lattice-matched to InP1
A problem arises, as quantum dots manufactured in the InP-based material systems naturally grow in dense e nsembles[4,5,6,7], resulting from the relatively small lattice mismatch between the QD and barrier materials

Summary

Introduction

Semiconductor quantum dots (QDs) are constantly attracting attention in various research fields, but the aspects on which the strongest emphasis is placed change from a decade to a decade. One of the most prominent features of the specific type of QDs that are made by self-assembly is their optical activity, i.e., the ability to absorb photons, which excite electrons from the valence-band to the conduction-band states, creating interacting electron-hole pairs called excitons Such nanostructures are formed of material coming from a strained layer of one semiconductor deposited on another one with mismatched lattice constant when fragmentation of the layer into nano-islands reduces the elastic energy of the system. There was a single report on similar behavior of InAs/ GaAs QDs with a strain-reducing layer, which was attributed to a strong variation of average In content within QD ensemble with a specific form of composition gradient within a QD27 Determination of such an atypical trend is practically essential, as it has to be taken into account when studies exploiting exciton excited states are performed. The typical increasing trend of exciton s–p-shell splitting versus emission energy is absent

Methods

Results

Conclusion