Controlled Charge Switching on a Single Donor with a Scanning Tunneling Microscope

Abstract

The charge state of individually addressable impurities in semiconductor material was manipulated with a scanning tunneling microscope. The manipulation was fully controlled by the position of the tip and the voltage applied between tip and sample. The experiments were performed at low temperature on the (110) surface of silicon doped GaAs. Silicon donors up to 1 nm below the surface can be reversibly switched between their neutral and ionized state by the local potential induced by the tip. By using ultrasharp tips, the switching process occurs close enough to the impurity to be observed as a sharp circular feature surrounding the donor. By utilizing the controlled manipulation, we were able to map the Coulomb potential of a single donor at the semiconductor-vacuum interface.

Tuning the electron transport at single donors in zinc oxide with a scanning tunnelling microscope

“…In addition, an equidistant sequence of vibronic excitations (vertical bars) is observed. The peak at positive sample bias (marked 0/ þ ) corresponds to the voltage required to shift the donor state above the Fermi energy of the sample, which changes the charge of the donor from neutral to þ e. Such ionization signatures in dI/dV spectra have also been observed on subsurface dopants in other semiconductors 6,23 , topological insulators 24 and molecular thin films 25 , as well as on adatoms on graphene 26 . The donor of Fig.…”

“…Moreover, spin 3 or charge 4 states of single dopants have been proposed as key components of a solid-state quantum computer. The scanning tunnelling microscope (STM) has been used to characterize defect states of single dopants 2 and to manipulate their position and charge state [5][6][7][8] . There are predictions that double donors, which can deliver two electrons, may be particularly useful for addressing spin states in quantum computers 9,10 .…”

Laser and voltage manipulation of bistable Si dopants in the GaAs (110) surface

“…To estimate if these effects are relevant in our experiments, we studied the size of donor Si rings of ionization as a function of applied laser power. 9 There was no visible change in ring size with the laser power up to four times higher than the values used in the rest of the experiments, meaning the change in TIBB due to illumination is negligible. Furthermore, a decrease of TIBB cannot explain the observed occupation of the bright state being due to illumination, because this situation would favor the dark state.…”

“…8 Ionization of the shallow donor state occurs at positive sample bias voltages, due to the local upward tip-induced band bending (TIBB). 9 Similarly, at these tunneling conditions, Si acceptors in GaAs appear dark because they are negatively charged.…”

“…The energy difference between the neutral and positive donor state can be overcome by the presence of the STM tip through upward TIBB, leading to clear rings of ionization appearing in the STM images. 9 At the other lattice coordinate, the interstitial configuration exists, indicated in black, which is either neutral plus one electron in the bulk Si 0 i or negatively charged Si − i . The neutral interstitial configuration has not been observed by STM measurements.…”