Today, talk by Uri Banin (The Hebrew University of Jerusalem) at 11 am in Amphi Boreau.

Heavily doped semiconductor nanocrystals.

Uri Banin. Institute of Chemistry & the Center for Nanoscience and Nanotechnology. The Hebrew University of Jerusalem, Jerusalem 91904, Israel.

Doping of bulk semiconductors, the process of intentional introduction of impurity atoms into a crystal discovered back in the 1940s, is a key enabling route for tuning their properties. Its introduction allowed the wide-spread application of semiconductors in electronic and electrooptic components. Controlling the size and dimensionality of semiconductor structures is an additional powerful way to tune their properties via quantum confinement effects. In this respect, colloidal semiconductor nanocrystals have emerged as a family of materials with size dependent optical and electronic properties that  have attracted significant attention due to their unique attributes and potential applications. Impurity doping in such colloidal nanocrystals still remains an open challenge. From the synthesis side, the introduction of a few impurity atoms into a nanocrystal which contains only a few hundred atoms may lead to their expulsion to the surface or compromise the crystal structure. From a physical viewpoint, impurities inherently create a heavily doped nanocrystal under strong quantum confinement, and the electronic and optical properties in such circumstances are still unresolved. We developed a solution based method to dope semiconductor nanocrystals with metal impurities providing control of the band gap and Fermi energy. A combination of optical measurements, scanning tunnelling spectroscopy and theory revealed the emergence of a confined impurity band and band-tailing effects. Successful control of doping and its understanding provide n- and  p-doped semiconductor nanocrystals which greatly enhance the potential application of such materials in solar cells, thin-film transistors, and optoelectronic devices prepared by facile bottom-up methods.