In the framework of the CERN-RD50 Collaboration, the adoption of p-type substrates has been proposed as a suitable mean to improve the radiation hardness of silicon detectors up to fluencies of 1times10 16 n/cm2. In this work two numerical simulation models will be presented for p-type and n-type silicon detectors, respectively. A comprehensive analysis of the variation of the effective doping concentration (Neff), the leakage current density and the charge collection efficiency as a function of the fluence has been performed using the Synopsys T-CAD device simulator. The simulated electrical characteristics of irradiated detectors have been compared with experimental measurements extracted from the literature, showing a very good agreement. The predicted behaviour of p-type silicon detectors after irradiation up to 1016 n/cm2 shows better results in terms of charge collection efficiency and full depletion voltage, with respect to n-type material, while comparable behaviour has been observed in terms of leakage current density

Numerical Simulation of Radiation Damage Effects in p-Type and n-Type FZ Silicon Detectors

This review paper discusses radiation effects in a variety of optoelectronic devices. The main emphasis is on displacement and total dose damage under conditions that are representative of various space missions. However, the mechanisms for degradation in space are also applicable to other environments, such as nuclear reactors, and the extremely high-energy particles associated with the Large Hadron Collider at CERN. In addition to permanent damage effects, there is also an abbreviated treatment of single-event effects in optoelectronic devices.

Radiation Effects in Optoelectronic Devices

Future high-luminosity colliders, such as the Super-LHC at CERN, will require pixel detectors capable of withstanding extremely high radiation damage. In this article, the performances of various 3D detector structures are simulated with up to 1 × 10 16  1 MeV- n eq / cm 2 radiation damage. The simulations show that 3D detectors have higher collection efficiency and lower depletion voltages than planar detectors due to their small electrode spacing. When designing a 3D detector with a large pixel size, such as an ATLAS sensor, different electrode column layouts are possible. Using a small number of n + readout electrodes per pixel leads to higher depletion voltages and lower collection efficiency, due to the larger electrode spacing. Conversely, using more electrodes increases both the insensitive volume occupied by the electrode columns and the capacitive noise. Overall, the best performance after 1 × 10 16  1 MeV- n eq / cm 2 damage is achieved by using 4–6 n + electrodes per pixel.

Simulations of radiation-damaged 3D detectors for the Super-LHC

A new "double sided" 3D solid-state detector structure, intended to simplify the 3D fabrication process, is proposed. In this structure, electrode columns of different doping types are etched from opposite sides of the substrate, with neither set of columns passing through the full substrate thickness. Simulations of the electrostatic and charge collection behavior in this structure have been made with ISE-TCAD to investigate its advantages and disadvantages and optimize its design. The device was shown to have a low depletion voltage, a short charge collection time, and a similar electric field distribution to a conventional 3D detector. However, near the front and back surfaces of the structure the electric field is lower and the charge collection time is longer. It is concluded that using this "double sided" 3D structure is not expected to significantly alter the device's behavior, and has advantages for fabrication.

Simulation Results From Double-Sided 3-D Detectors

In this work we propose a new combined TCAD radiation damage modelling scheme, featuring both bulk and surface radiation damage effects, for the analysis of silicon detectors aimed at the High Luminosity LHC. In particular, a surface damage model has been developed by introducing the relevant parameters ( $\text {N}_{\mathrm {OX}}$ , $\text {N}_{\mathrm {IT}}$ ) extracted from experimental measurements carried out on p-type substrate test structures after gamma irradiations at doses in the range 10-500 Mrad(Si). An extended bulk model, by considering impact ionization and deep-level cross-sections variation, was included as well. The model has been validated through the comparison of the simulation findings with experimental measurements carried out at very high fluences ( $2\times 10^{16}\,\,1$ MeV equivalent n/cm2) thus fostering the application of this TCAD approach for the design and optimization of the new generation of silicon detectors to be used in future HEP experiments.

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Combined Bulk and Surface Radiation Damage Effects at Very High Fluences in Silicon Detectors: Measurements and TCAD Simulations

The very high radiation fluence expected at LHC (Large Hadron Collider) at CERN will induce serious changes in the electrical properties of the silicon detectors that will be used in the internal layers of the experiments (ATLAS, CMS, LHCb). To understand the influence of the fabrication technology in the radiation-induced degradation, silicon detectors were fabricated simultaneously with the three different possible technologies, P-in-N, N-in-N, and N-in-P, on standard and oxygenated float-zone silicon wafers. The diodes were irradiated with protons to fluences up to 10/sup 15/ cm/sup -2/. The measurements of the electrical characteristics, current-voltage and capacitance-voltage, are presented for the detectors manufactured with the three technologies. In terms of alpha factor (leakage current) the three technologies behave similarly. In terms of beta factor (effective doping concentration) N-in-P devices show the best performances.

Comparison of radiation hardness of P-in-N, N-in-N, and N-in-P silicon pad detectors

High oxygen concentration in silicon increases the resistance of radiation detectors to high radiation doses. Unfortunately, high-resistivity float zone (FZ) silicon, needed for radiation detectors, has too low an oxygen content. The solution to this is silicon oxygenation. There are different ways of incorporating oxygen into silicon. The most accepted one is by high-temperature diffusion from a thick SiO 2 layer. In this paper, we investigate the impact of this silicon oxygenation technique as well as the application of different gettering techniques to improve the minority carrier lifetime of high-resistivity FZ silicon substrates for radiation detectors. The minority carrier lifetimes before and after surface etching have been measured on samples subjected to different oxygenation and gettering treatments by using a quasi steady-state photoconductance technique. A lifetime improvement efficiency factor is defined for each treatment process. The lifetime efficiency factors behave independently, so that the lifetime efficiency factors associated with different sequential combinations of treatments can be estimated by a multiplicative combination. Different gettering techniques that improve or degrade the minority carrier lifetime are analyzed, and the best options for silicon radiation detector fabrication are determined. Oxygenated silicon with a minority carrier lifetime close to I ms can be obtained.

M. Key

Papers

Comparison of radiation hardness of P-in-N, N-in-N, and N-in-P silicon pad detectors

Effect of Combined Oxygenation and Gettering on Minority Carrier Lifetime in High-Resistivity FZ Silicon