Effect of small shape changes on the optical response of highly symmetric silicon quantum dots

Ellipsoidal quantum dot structures are proposed and studied with ab inito calculations. A comparison of the formation energy with spherical partners shows small differences. However, electronic and optical properties are distinct. Because electronic states have different sensitivities to aspect ratio changes, selected frontier orbitals are driven into the gap and an overall level shifting allows for absorption in the visible range. Our result shows the importance of both size and shape for the gap engineering of silicon quantum dots.