Electronic properties of chalcogenide semiconductor nanostructures and thin-films

I will review our combined local-probe and transport measurements on three types of semiconductor chalcogenide systems. Starting with Cu2S nanocrystals, I will present a new method for achieving p-type doping, by which Cu vacancies are formed upon annealing at moderate temperatures, yielding free holes. Consequently, the conductance of Cu2S nanocrystals arrays increases by 4-6 orders of magnitude. This method enable patterned doping by applying focused laser illuminations. Next, I will discuss the origin of the surprisingly high conversion efficiency of polycrystalline Cu(In, Ga) Se solar-cells, focusing on the role of grain-boundaries. Local-probe scanning tunneling spectroscopy (STS) and conductive-probe atomic force microscopy measurements provide evidence for significant band-bending at grain-boundaries, assisting the collection efficiency of photo-generated minority (electron) charges, and reduced deep-level density of states, reducing the recombination rate. Finally, STS measurements on CdSe nanoplatelets will be presented, providing first evidence for a unique two-dimensional behavior and quantumconfinement associated with their thickness only.