Strain‐Tunable Photoluminescence From Ge Quantum Dots on Si Nanotips for CMOS‐Compatible Photonics

ABSTRACT In this work, a combined experimental and modeling study of strain effects on the radiative emission of Ge quantum dots (QDs) grown on Si nanotips (NTs) is presented. Pure germanium QDs with heights of 30 and 70 nm are deposited on top of Si NTs using solid‐source molecular beam epitaxy. The micro‐photoluminescence measurements show a blueshift of the peak emission from to eV as the QD height increases from 30 to 70 nm, respectively. To understand this effect, strain in Ge QDs and Si NTs is analyzed using X‐ray diffraction. An in‐plane compressive strain of % is observed in the Ge QDs, while the Si NT substrate exhibits an in‐plane tensile strain of about 2.9 %. Furthermore, the electronic band structure calculations employing single‐band method coupled to the computation of the elastic strain tensor using continuum elasticity are performed. The results indicate that the unusual size dependence of Ge QD emission is due to a combination of (i) strain in Ge QDs, (ii) prominence of ‐direct electron–hole transitions for larger Ge QDs over ‐indirect ones more frequent in smaller dots. Finally, transitions involving electrons and heavy‐ and light‐hole states are identified.