Excitation intensity dependence of photoluminescence spectra of SiGe quantum dots grown on prepatterned Si substrates: Evidence for biexcitonic transition

TL;DR

This study investigates how photoluminescence spectra of ordered SiGe quantum dots depend on excitation intensity, revealing biexcitonic transitions at higher intensities and confirming theoretical energy calculations.

Contribution

It provides experimental evidence for biexcitonic transitions in SiGe quantum dots and correlates these with theoretical models, advancing understanding of excitonic interactions.

Findings

Biexcitonic transitions appear at excitation intensities above 3 W/cm^2.

Photoluminescence bands shift to higher energies with increased excitation.

Experimental energies match theoretical calculations of exciton and biexciton states.

Abstract

The pumping intensity (I) dependence of the photoluminescence (PL) spectra of perfectly laterally two-dimensionally ordered SiGe quantum dots on Si(001) substrates was studied. The PL results from recombinations of holes localized in the SiGe quantum dots and electrons localized due to the strain field in the surrounding Si matrix. The analysis of the spectra revealed several distinct bands, attributed to phonon-assisted recombination and no-phonon recombination of the excitonic ground state and of the excited excitonic states, which all exhibit a linear I dependence of the PL intensity. At approximately I>3W/cm^2, additional bands with a nearly quadratic I dependence appear in the PL spectra, resulting from biexcitonic transitions. These emerging PL contributions shift the composite no-phonon PL band of the SiGe quantum dots to higher energies. The experimentally obtained energies of the no-phonon transitions are in good agreement with the exciton and biexciton energies calculated using the envelope function approximation and the configuration interaction method.