Summary: Binary oxides such as SnO2 are traditionally used as highly
conductive transparent contacts and in chemical sensors.
Understanding and controlling the conductivity of high quality SnO2
can improve the existing applications and enable new applications
as transparent electronics and optoelectronics.
The conductivity of SnO2 is characterized by an unintentional n-
type conductivity of the bulk and a surface electron accumulation
layer that provides the sensor functionality and strongly influences
electrical contacts to SnO2.
The group of Prof. Speck has grown high-quality SnO2 films with
controlled doping and characterized the film conductivity. They
have demonstrated n-type doping by antimony with 100% doping
efficiency for conductivities up to those used in transparent
contacts. On the other end of the conductivity scale, indium doping
was shown to provide insulating SnO2 by acting as an acceptor that
compensates the unintentional n-type donors. The surface
accumulation layer has been demonstrated to be caused by Fermi-
level pinning in the conduction band at the SnO2 surface. The
ability to remove the accumulation layer by an oxygen plasma
treatment enables the control of the contact properties.