Science 332, 77–81 (2011)

The ability to control the electronic properties of semiconductors is a foundation of the electronics industry. Such control can be achieved by doping impurity atoms into bulk crystalline semiconductors, as well as by controlling the size of reduced-dimension semiconductors such as quantum dots. However, combining these methods — doping quantum dots — has proved to be experimentally difficult. Now, Oded Millo, Eran Rabani, Uri Banin and colleagues at Hebrew University and Tel Aviv University have demonstrated a simple method of doping metal atoms into semiconducting quantum dots.

The researchers added a solution of metal salts to a solution of indium arsenide quantum dots (both dissolved in toluene) at room temperature. Solid-state diffusion then carried some metal atoms into the quantum dot crystal lattices, as confirmed by photoelectron spectroscopy. Different metal salts introduced different metal atoms, with distinct effects: copper atoms were incorporated into the crystal interstices, and added negative charges to the quantum dot, whereas silver atoms replaced indium atoms, and added positive charges. Absorption and emission wavelengths were shifted, reflecting changes to the dot's density of states and Fermi level, and the formation of impurity-derived energy bands.