Depth-dependent charge collection profile of pad diodes

TL;DR

This study measures how charge collection varies across the depth of pad diodes using a high-energy electron beam, revealing uniformity in non-irradiated diodes and depth-dependent effects in irradiated ones.

Contribution

It introduces an in-situ alignment procedure and provides detailed charge collection profiles as a function of depth for both irradiated and non-irradiated diodes.

Findings

Non-irradiated diode shows uniform charge collection above full depletion.

Irradiated diode exhibits non-uniform charge profile that varies with bias voltage.

Charge collection efficiency depends on diode irradiation and bias conditions.

Abstract

The collected charge of two pad diodes is measured along the diode width using a 5:2 GeV electron beam at the DESY II beam test facility. The electron beam enters parallel to the readout electrode plane and perpendicular to the edge of the diode. The position of the electron beam is reconstructed by three planes of an EUDET-type telescope. An in-situ procedure is developed to align the diode surface parallel to the electron beam. The result of these measurements is the charge collection efficiency profile as a function of depth for each diode. For a non-irradiated diode, the charge profile is uniform as a function of the beam position for bias voltages above the full-depletion, as expected. For the irradiated diode, the charge profile is non-uniform and changes as a function of bias voltage.