MSE SEMINAR SERIES: Martin Wenderoth Talk Title: "Scanning Tunneling Microscopy Playing with electric fields on the atomic scale"
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.