Charge carrier generation in RNDR-DEPFET Detectors

TL;DR

The paper investigates charge carrier generation in RNDR-DEPFET detectors for direct detection of light dark matter via electron recoils in silicon. It presents a 64×64 RNDR-DEPFET prototype (DANAE) and an exposure-sweep characterization to extract the charge-generation rate, using extensive data filtering and pixel clustering to suppress defects. Results show a time-dependent generation rate of $R_{Gen}=15^{+45}_{-10}$ e$^-$ per pixel per day, plus a substantial time-independent background offset of about $560\,\mu$g readout per day, indicating background sources beyond bulk generation. The work demonstrates the detector’s high time resolution and outlines paths to reduce background through production improvements, dedicated pre-readout clearing, and temperature-calibrated measurements, enabling better sensitivity for rare electron-recoil events in dark matter searches.

Abstract

Depleted p-channel field effect transistor detectors with repetitive-non-destructive readout (RNDR-DEPFETs) achieve a deep sub-electron noise by averaging several independent measurements of one single event. During the repetitive readout collected electrons are transferred between two readout nodes within each pixel to enable electron number-resolved measurements. The pixels serve as a unit cell of an active pixel sensor to achieve a high level of parallelization and fast readout. These properties are exploited in the DANAE experiment, which aims for the direct detection of light dark matter based with the event signature of electron recoils. We present the experimental characterization of an $64\times64$ RNDR-DEPFET pixel detector with a focus on the charge carrier generation rate. This technology achieves a high time resolution, which increases its sensitivity on rare events with a signal of two or more electrons due to the Poisson distribution of thermal generated electrons.

Figures (11)

• Figure 1: RNDR-DEPFET schematic: Electrons are collected in the internal gate to modify the conductivity of the transistor channel. An RNDR-DEPFET pixel hosts two sub-pixels to interchange electrons for repetitive readout DEPFETBaehr.
• Figure 2: The recorded raw data spectrum for 110 pixels after 800 repetitions and a single sampling of 1,3s.
• Figure 3: The hit map for an total exposure time of 2,22s.
• Figure 4: The percentage of pixels with events are plotted against the number of frames. The red values are removed.
• Figure 5: The width and its uncertainty for the gauss fit are shown for an exposure time of 1,3s. For column 34, the width of the Gaussian fit is abnormally large, meaning there is a lot of noise. This is probably due to defects in this readout channels.