Measurements of low gain diodes using Transient Current Technique

Thin silicon sensors are under investigation for the LHC upgrade (High Luminosity LHC) next decade. Thin sensors have better momentum resolution than thick ones due to reduced multiple scattering. Having a thin sensor with built-in amplification allows, in addition, to reduce the thickness without significant signal loss. These diodes have a built-in amplification layer that allows to obtain a higher signal than that of a standard diode of the same thickness. Two different techniques were employed to characterize them. Measurements of capacitance and leakage current versus bias voltage to extract the depletion voltage, and Transient Current Technique (TCT) to calculate the absolute gain of the device. Red laser is used for TCT to determine properties of charge carrier's motion. The gain of four samples is calculated with a method we call "kink method" which uses the ratio of charge induced by holes to charge induced by electrons. We also used a second method based on comparing the collected charge with a reference diode.