First observation of the charge carrier density related gain reduction mechanism in LGADs with the Two Photon Absorption-Transient Current Technique

Abstract

The Low Gain Avalanche Detector (LGAD) technology is very promising for silicon timing detectors and currently heavily researched. Recent studies show that the gain of LGADs highly depends on the charge carrier density inside the gain layer. To study the charge carrier density related gain reduction, the Two Photon Absorption-Transient Current Technique (TPA-TCT) was employed to obtain information on the drift velocity and electric field of a LGAD for different charge carrier densities. The TPA-TCT uses fs-pulse infrared lasers to provide a three-dimensional resolution to study bulk effects. A compact TPA-TCT setup was developed at CERN and is used to measure current transients against the device depth of a 285μm thick PIN and LGAD, fabricated by IMB-CNM. Methods to extract information about the electric field are employed to verify the charge carrier density related gain reduction. The gain layer of the LGAD is spatially resolved for the first time.