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Description
The charge collection of two $\text{n}^+\text{p}^+\text{p}^+$ pad diodes has been measured using a $5 \; \text{GeV}$ electron beam (at DESY) entering from the $150 \; \mu \text{m}$ thick side edge side of diodes. Using the EUDAQ telescope it is possible to precisely reconstruct the beam position. The collected charge as a function of the beam position along the diode thickness is investigated.
This measurement technology is novel and comparable to the better-known edge-TCT. The alignment of the beam direction with respect to the diode surface was done online during the data taking.
The diodes have an area of $25 \;\text{mm}^2$ and a p-doping concentration of $4\times10^{12}$ $\text{cm}^{-3}$. The measurements were performed at $ - 20~^\circ$C for bias voltages up to $\text{V}_{\text{bias}} = 800 \; \text{V}$. One diode was irradiated with $23 \;\text{MeV}$ protons to a $1 \;\text{MeV}$ neutron equivalent fluence of $\Phi_{\text{eq}}$ = $2\times10^{15}$ $\text{cm}^{-2}$. The second diode was not irradiated. For the non-irradiated diode, the charge profile is uniform as a function of the beam position. For the irradiated diode, the charge profile is non-uniform and the changes as the applied bias voltage.
This work presents the procedure of measurement and the online alignment along with the results obtained for two diodes.
