WhenMon, March 5, 2012, 4pm – 5pm
WhereWilsdorf 101 (map)
DescriptionThe challenge of the ever shrinking semiconductor devices has been a subject of
discussion for decades. In devices below a critical size doping or transport properties
cannot be described in a homogeneous model anymore. Using a low-temperature
scanning tunnelling microscope (STM) operating at 5 Kelvin we have studied the
impact of the electric field on single dopant atoms in GaAs in different configurations.
The discrete nature of the charge of a dopant atom in combination with the long
range Coulomb field results in a complex electrostatic potential landscape. Using the
voltage between tip and semiconductor across the vacuum barrier to manipulate the
potential landscape, we are able to control and to visualize the charge state of
individual and multi donor systems near the GaAs (110) surface. Using an STM
extended to a three-terminal geometry we have studied single acceptor atoms
exposed to an “in plane” electric field of a biased p-i-n diode. High-resolution
scanning tunnelling spectroscopy measurements show that the resonance channel
induced by the acceptor can be switched on and off. In a second type of experiment
we have used scanning tunnelling potentiometry to map local transport field near
localized scattering centers in a quasi 2D electron gas down to the nm scale.