Physics Colloquium, January 28, 2003

Pseudopotential Theory of Semiconductor Quantum Dots, Wires and Films

Alex Zunger

National Renewable Energy Laboratory

The electronic structure of nanostructures has almost universally addressed by the “standard model” of effective-mass k·p envelope function approach. While eminently successful for quantum wells, this model breaks down for small structures, in particular, for small dots and wires. Until recently, it was impractical to test the “standard model” against more general approaches that allow many-band (G-X-L) coupling. However, it is now possible, due to special tricks [1]-[2], to apply to all-band pseudopotential method to 103-106 atom nanostructures. This shows (i) how the “standard model” fails, for thin superlattices, (ii) how size effect lead to band gaps that differ from what is expected in effective-mass theory, (iii) that small dots of III-V materials have an indirect gap that converts to direct above a critical size, (iv) how the spectra of CdSe dots evolve from the bulk and how the spectra of dots of Si, GaAs, InP and CdSe compare with experiment, and how the use of pseudopotential wavefunctions leads to very different electron-hole coulomb and exchange energies relative to the “standard model,” (v) how theory predicts the charging spectra and fine-structure of self-assembled InAs/GaAs quantum dots.

3.30 p.m., Smith Laboratory, Room 1005

Refreshments served in Smith 1094 at 3:00 p.m.