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We present an in-depth investigation of the interpad (IP) gap region in the ultra-fast silicon detector (UFSD) Type 10, utilizing a femtosecond laser beam and the transient current technique (TCT) as probing instruments. The sensor, fabricated in the trench-isolated TI-LGAD RD50 production batch at the FBK Foundry, enables a direct comparison between TI-LGAD and standard UFSD structures. This research aims to elucidate the isolation structure in the IP region and measure the IP distance between pads, comparing it to the nominal value provided by the vendor. Our findings reveal an unexpectedly strong signal induced near p-stops. This effect is amplified with increasing laser power, suggesting significant avalanche multiplication, and is also observed at moderate laser intensity and high HV bias. This investigation contributes valuable insights into the IP region's isolation structure and electric field effects on charge collection, providing critical data for the development of advanced sensor technology for the Compact Muon Selenoid (CMS) experiment and other high-precision applications. [ABSTRACT FROM AUTHOR]

We present a setup for time-resolved spectroscopic ellipsometry in a pump–probe scheme using femtosecond laser pulses. As a probe, the system deploys supercontinuum white light pulses that are delayed with respect to single-wavelength pump pulses. A polarizer–sample–compensator–analyzer configuration allows ellipsometric measurements by scanning the compensator azimuthal angle. The transient ellipsometric parameters are obtained from a series of reflectance-difference spectra that are measured for various pump–probe delays and polarization (compensator) settings. The setup is capable of performing time-resolved spectroscopic ellipsometry from the near-infrared through the visible to the near-ultraviolet spectral range at 1.3 eV–3.6 eV. The temporal resolution is on the order of 100 fs within a delay range of more than 5 ns. We analyze and discuss critical aspects such as fluctuations of the probe pulses and imperfections of the polarization optics and present strategies deployed for circumventing related issues. [ABSTRACT FROM AUTHOR]

Transient dielectric functions with a 120 fs time resolution of Ge, Si, and InP were acquired from 1.7 to 3.5 eV with a femtosecond pump-probe rotating-compensator ellipsometer. The intensity of the pump laser (with 1.55, 3.10, or 4.65 eV photon energy) was adjusted to create an initial near-surface carrier density of 1020 cm−3. In Ge, there is a significant (∼15%) decrease in the E1 and E1 + Δ1 critical point absorption and a Kramers–Kronig consistent change in the refractive index because photoexcited electrons at L block these transitions and reduce their amplitudes. Only a small redshift of the E1 critical point is observed, which we attribute to lattice heating and exchange-correlation effects. Minimal changes were found for Si and InP, where electrons near Δ and Γ do not participate in interband transitions between 1.7 and 3.5 eV. [ABSTRACT FROM AUTHOR]

A feasibility study conducted at the laser facility ELI Beamlines confirms that fs-laser pulses can produce Single Event Effect (SEE), Single Event Upset (SEU) and Single Event Burnout (SEB) conditions in irradiated Low Gain Avalanche Detectors (LGADs) and the corresponding PIN diodes. A comprehensive and systematic study on PIN and LGAD mortality has been conducted to experimentally determine the stability, instability, and irreversible damage thresholds for LGADs and PINs exploiting a fs-laser system. Thresholds are given as sets of two parameters: bias voltage and laser pulse energy (energy deposition threshold). Using the Two-Photon Absorption (TPA) - Transient Current Technique (TCT) to study the mechanism that triggers SEU/SEB conditions in LGADs, as a function of illumination position establishes this technique as a promising tool for more advanced explorations of SEE, not only in LGADs but also in other Si-based sensors. To achieve these results, a highly flexible and versatile fs-laser-based TCT experimental setup has been developed at ELI Beamlines, allowing two TCT modalities with the same setup: Single Photon Absorption (SPA) at 800 nm laser wavelength and TPA at 1550 nm. [ABSTRACT FROM AUTHOR]

We present an investigation of the interpad region (IP) in the Ultra-Fast Silicon Detector (UFSD) Type 10, utilizing a femtosecond laser and the transient current technique (TCT). We elucidate the isolation structure and measure the IP distance between pads, comparing it to the nominal value provided by the vendor. A comparison of sensors with identical layouts but different nominal IP distances (49 μm vs. 61 μm) and different processing parameters revealed their significant different charge collection properties in the IP. • fs-laser TCT can characterize the isolation structures of the segmented LGADs. • Charge multiplication is observed in the interpad region of the segmented LGADs. • The strongest interpad charge multiplication is observed close to p-stop implants. • Interpad length and doping are critical for charge multiplication between the pads. • Drop in interpad gap and increase of doping boost interpad charge multiplication. [ABSTRACT FROM AUTHOR]