Charge-Carrier transport simulations in diamond detectors with electric-field-dependent mobility and charge-collection-distance-based trapping

Abstract

Diamond detectors are attractive for operation in harsh radiation environments because they combine radiation tolerance, fast signal formation, and low leakage current. Realistic detector-response simulations require an accurate description of charge-carrier mobility and trapping, which determine both signal amplitude and timing. In this work, we extend \allpix{}, a modular end-to-end detector simulation framework, with diamond-specific transport models. The implementation includes field-dependent mobility parameterizations for electrons and holes and an effective trapping model based on the charge collection distance (CCD), providing a detector-level interface to material quality and radiation-damage measurements. The mobility description is validated in the negligible-trapping limit using single-crystalline CVD diamond by comparing simulated drift velocities and transient-current signals with published reference data. For polycrystalline CVD diamond, the CCD-based trapping model is evaluated using experimentally measured CCD values and compared with laboratory transient-current-technique waveforms. The simulations reproduce the measured drift-velocity behavior in scCVD and the reduced charge collection and degraded transient response observed in pcCVD. The presented implementation enables detector-level studies of charge collection, pulse formation, and timing performance in diamond sensors using experimentally accessible transport and trapping parameters, and provides a practical framework for simulation-driven detector development and radiation-damage studies.

Figures (11)

• Figure 1: Leakage current as a function of applied bias. Data are shown without pumping (blue) and after 20 min pumping (red).
• Figure 2: Detector capacitance as a function of applied bias. Data are shown before pumping (blue) and after 20 min pumping (red).
• Figure 3: Landau + Gaussian distribution (using Sr-90) at an electric field of 0.4Vµm fitted with langau model to events accepted by the three selection criteria mentioned in Sec.\ref{['subsec:event_selection_criteria']}.
• Figure 4: CCD of pcCVD diamond, extracted from $^{90}$Sr spectra as a function of $|E|=|V|/d$. Results are shown for both bias polarities in the unpumped state (blue) and after $\sim$20 min $\beta$-pumping (red). Error bars denote the statistical uncertainty of the MPV from the Landau--Gaussian (Langau) fit.
• Figure 5: Mean measured transient current waveforms at $E=1V\per µm$ for (a) electrons and (b) holes. The markers indicate the characteristic timing points used in the waveform analysis, namely the 10%, 50%, and 90% level crossings on the leading and trailing edges, together with the peak position. The corresponding values of the peak amplitude, rise time, fall time, full width at half maximum (FWHM), and edge-defined pulse width are reported in each panel.