  For the Phase-II Upgrade of the ATLAS detector at CERN, the current ATLAS
Inner Detector will be replaced with the ATLAS Inner Tracker. The ATLAS Inner
Tracker will be an all-silicon detector, consisting of a pixel tracker and a
strip tracker. Sensors for the ITk strip tracker are required to have a low
leakage current up to bias voltages of -700 V to maintain a low noise and power
dissipation. In order to minimise sensor leakage currents, particularly in the
high-radiation environment inside the ATLAS detector, sensors are foreseen to
be operated at low temperatures and to be manufactured from wafers with a high
bulk resistivity of several k{\Omega} cm. Simulations showed the electric field
inside sensors with high bulk resistivity to extend towards the sensor edge,
which could lead to increased surface currents for narrow dicing edges. In
order to map the electric field inside biased silicon sensors with high bulk
resistivity, three diodes from ATLAS silicon strip sensor prototype wafers were
studied with a monochromatic, micro-focused X-ray beam at the Diamond Light
Source. For all devices under investigation, the electric field inside the
diode was mapped and its dependence on the applied bias voltage was studied.
The findings showed that the electric field in each diode under investigation
extended beyond its bias ring and reached the dicing edge.
