Abstract: Single dopant atoms in a semiconductor matrix are of interest in condensed matter physics, quantum computation, materials science, and nanotechnology. In this brief review, we survey our recent experimental progress in the scanning tunneling microscopy and spectroscopy of monomers and dimers of double-donor impurity atoms in the wide band gap semiconductor ZnO. We observed that tip-induced band-bending leads to the ionization of isolated doubledonors as well as vibrational excitation. Furthermore, it turned out that subsurface impurities may be pushed and pulled in a controllable way using a scanning tunneling microscope tip. Spectroscopic maps of donors exhibit features that are closely related to those observed from single-electron transistors, and enable the determination of important parameters by simple modeling. Donor excitation spectra show that strongly coupled dimers of double donors may be used to construct double quantum dots with minimal size. This may be viewed as a step towards quantum electronics with an atomic-scale structure.

Key words: scanning tunneling microscopy, single donor, ionization, vibration, single electron transistor, double quantum dot