  The breakdown voltage of silicon sensors without special surface is known to
be affected by the ambient humidity. To understand the sensor's humidity
sensitivity, Synopsys TCAD was used to simulate n-in-p test structures for
different effective relative humidity. Photon emission of hot electrons was
imaged with a microscope to locate breakdown in the edge-region of the sensor.
The Top-Transient Current Technique was used to measure charge transport near
the surface in the breakdown region of the sensor. Using the measurements and
simulations, the evolution of the electric field, carrier densities and
avalanche breakdown in the periphery of p-bulk silicon sensors is presented.
