Modeling of surface-state induced inter-electrode isolation of n-on-p devices in mixed-field and γ-irradiation environments

In the HEP-experiments of High Luminosity upgrade of the Large Hadron Collider (HL-LHC), the application of isolation implants like p-stop between n⁺-electrodes of position sensitive n-on-p sensors has been typically considered to counter the detrimental effect on position resolution of the accumulation of positive net oxide charge with radiation. In addition to the positively charged layer close to the Si/SiO₂-interface, surface damage introduced by radiation in SiO₂-passivated silicon particle detectors includes the accumulation of trapped-oxide-charge and interface traps. A previous study of either n/γ (mixed field)- or γ-irradiated Metal-Oxide-Semiconductor (MOS) capacitors showed evidence of substantially higher introduction rates of acceptor- and donor-type deep interface traps (Nᵢt,acc/don) in mixed-field environment. In this work, an inter-electrode resistivity (ρᵢnt) TCAD-simulation study of n-on-p sensors with and without p-stop isolation implants was conducted for both irradiation types. Higher levels of ρᵢnt showed correlation to higher densities of deep Nᵢt,acc/don, with the isolation performance of the mixed-field irradiated sensors becoming independent of the presence of p-stop implant between the n⁺-electrodes throughout the investigated dose range up to about 100 kGy. The low introduction rates of deep Nᵢt,acc/don in γ-irradiated sensors resulted in high sensitivity of ρᵢnt to the presence and peak doping of p-stop above the lowest dose of 7 kGy in the study. Because of the advantageous influence of radiation-induced accumulation of deep Nᵢt on the inter-electrode isolation, position sensitive n-on-p sensors without isolation implants may be considered for future HEP-experiments where the radiation is largely due to hadrons.