X-ray Response of the Fully-Depleted, p-Channel SiSeRO-CCD

Abstract

We present an X-ray characterization of a fully depleted, 725 $μ$m thick p-channel SiSeRO CCD. Measurements with a $^{55}$Fe source yield an energy resolution of $54 \pm 0.9$ eV ($14.6 \pm 0.25 e^{-}$) at 5.9 keV for single-pixel events, demonstrating that the SiSeRO amplifier preserves the intrinsic charge resolution of the CCD under multi-sample non-destructive readout. Characterization with a $^{241}$Am source extends the response to higher-energy photons, with reconstructed spectral features observed between 9-26 keV and the 59.5 keV $γ$ emission. These measurements, together with a muon-derived diffusion calibration, show that charge transport and diffusion are consistent with interactions spanning the full sensor depth. These results demonstrate that the SiSeRO CCD simultaneously achieves sub-electron noise performance and efficient charge collection in a thick, fully depleted silicon detector. This combination enables X-ray spectroscopy across a broad energy range while maintaining sensitivity to faint signals.

Figures (5)

• Figure 1: Overview of the SiSeRO-CCD architecture and experimental setup used for detector characterization. (a) Schematic top and cross-sectional views of the SiSeRO output amplifier, illustrating the integration of an n-MOSFET within the CCD p-channel and the principle of non-destructive readout (NDR). (b) Photograph of the experimental setup, including the vacuum chamber, readout electronics, and optical excitation components.
• Figure 2: Histogram of pixel values in the overscan region, showing discrete charge peaks corresponding to integer numbers of electrons (starting at zero). Black points show the data, and the blue curve shows the best-fit multi-Gaussian model used to extract the gain and read noise. The clear separation of the single-electron peaks demonstrates sub-electron read noise and enables precise conversion between ADU and collected charge.
• Figure 3: Reconstructed $^{55}$Fe spectrum for single-pixel events ($n_{\mathrm{pix}} = 1$). Black points show the data, and the blue curve shows the best-fit model to the Mn $K\alpha$ and $K\beta$ lines. The fit parameters, including the peak centroids and energy resolution, are shown in the inset.
• Figure 4: Transverse diffusion variance $\sigma_t^2$ as a function of nominal depth $z$ extracted from through-going cosmic muons. Points show the Gaussian widths (squared) obtained from stacked transverse charge distributions in each depth bin, with error bars corresponding to the statistical uncertainties of the fits. The solid curve shows the best-fit diffusion model (see Eq. \ref{['eqn: diffusion']}). The observed increase of $\sigma_t^2$ with depth reflects the growth of lateral charge diffusion with drift distance in the fully depleted sensor.
• Figure 5: Reconstructed $^{241}$Am energy spectrum measured with the SiSeRO detector. Black points show the data (counts per 200 eV bin), and the blue curve shows the best-fit model. The model describes the fluorescence lines in the 9--26 keV range with an energy-dependent resolution and linear background, and is used to establish the energy calibration. The 59.5 keV $\gamma$ line is shown but excluded from the fit.