Strain-graded quantum dots with spectrally pure, stable and polarized emission

Structural deformation modifies the bandgap, exciton fine structure and phonon energy of semiconductors, providing an additional knob to control their optical properties. The impact can be exploited in colloidal semiconductor quantum dots (QDs), wherein structural stresses can be imposed in three dimensions while defect formation is suppressed by controlling surface growth kinetics. Yet, the control over the structural deformation of QDs free from optically active defects has not been reached. Here, we demonstrate strain-graded CdSe-ZnSe core-shell QDs with a compositionally abrupt interface by coherent pseudomorphic heteroepitaxy. Resulting QDs tolerate mutual elastic deformation of varying magnitudes at the interface with high structural fidelity, allowing for spectrally stable and pure emission of photons at accelerated rates with near unity luminescence efficiency. We capitalize on the asymmetric strain effect together with the quantum confinement effect to expand the emission envelope of QDs spanning the entire visible region and exemplify their use in photonic applications.

Dongju Jung, Jeong Woo Park, Sejong Min, Hak June Lee, Jin Su Park, Gui-Min Kim, Doyoon Shin, Seongbin Im, Jaemin Lim, Ka Hyung Kim, Jong Ah Chae, Doh C. Lee, Raphaël Pugin, Xavier Bulliard, Euyheon Hwang, Ji-Sang Park, Young-Shin Park, Wan Ki Bae