Extended excitons and compact helium-like biexcitons in type-II quantum dots

TL;DR

This study investigates type-II InP/GaAs quantum dots using magneto-photoluminescence, revealing excitonic properties, tunable hole occupancy, and a transition from excitonic to biexcitonic emission regimes under varying excitation powers and magnetic fields.

Contribution

It provides detailed measurements of excitonic and biexcitonic states in type-II quantum dots, highlighting the tunability of electron-hole interactions and the transition between different emission regimes.

Findings

Excitonic Bohr radius estimated at 15nm

Binding energy approximately 1.5 meV

Transition from excitonic to biexcitonic emission with increasing excitation power

Abstract

We have used magneto-photoluminescence measurements to establish that InP/GaAs quantum dots have a type-II (staggered) band alignment. The average excitonic Bohr radius and the binding energy are estimated to be 15nm and 1.5 meV respectively. When compared to bulk InP, the excitonic binding is weaker due to the repulsive (type-II) potential at the hetero-interface. The measurements are extended to over almost six orders of magnitude of laser excitation powers and to magnetic fields of up to 50 tesla. It is shown that the excitation power can be used to tune the average hole occupancy of the quantum dots, and hence the strength of the electron-hole binding. The diamagnetic shift coefficient is observed to drastically reduce as the quantum dot ensemble makes a gradual transition from a regime where the emission is from (hydrogen-like) two-particle excitonic states to a regime where the emission from (helium-like) four-particle biexcitonic states also become significant.