A donor molecule in silicon

In 1954 Kohn and Luttinger introduced the description for a single donor in silicon as a hydrogen atom analogue in a semiconductor environment. Generalizing the concept, a donor pair may behave as a hydrogen molecule. However, a detailed understanding of the electronic structure of these molecular systems is a challenge to be overcome. Here we present an experimental demonstration of the energy spectrum of a strongly interacting donor pair in the channel of a silicon nanotransistor. We show the first evidence of a simultaneous enhancement of the binding and charging energies with respect to the single donor spectrum as well as a measurable exchange coupling. The measured data can be accurately matched by an effective mass theory incorporating the Bloch states multiplicity in Si, a central cell donor corrected potential and a full configuration interaction. These results suggest a novel physical mechanism to increase the operation temperature of conventional single-atom transistors and improve their robustness against interfacial electric fields. Furthermore, the data describes the Kane basic quantum processing element in the range of molecular hybridization.