Speaker
Description
We present a study of the forward and reverse currents in silicon pad diodes irradiated to extreme neutron fluences of up to $1 \times 10^{18}\,n_{eq}/$cm$^2$, slightly more than the expected fluences at the innermost radii of tracking detectors at a future circular hadron collider.
At such high fluences, the low-doped silicon bulk and the highly doped implant no longer behave like a typical pn diode. Excess free carriers are trapped at radiation-induced deep defects, compensating ionized shallow defects in the bulk. Consequently, the carrier concentrations in the bulk decrease and become similar to those in intrinsic silicon, increasing the resistivity of the bulk. The interaction between ionized defects and free carriers leads to increased Coulomb scattering, causing a decrease in the low-field carrier mobilities with fluence.
To quantify the mobility degradation caused by ionized impurity scattering as a function of fluence and to obtain a qualitative understanding of the diode’s electrical performance, current-voltage characteristics were measured for fluences ranging from $9 \times 10^{14}$ to $1 \times 10^{18}\,n_{eq}/$cm$^2$ at various temperatures. These measurements are compared to TCAD simulations using different radiation-damage models to evaluate their ability in reproducing the observed currents at such extreme fluences, and to gain insight into the underlying physical processes driving these changes.