The Problem of Extracting Transit Times from Transient Current Signals of Diamond Detectors in TCT Experiments

Abstract

Transient-current technique (TCT) measurements are widely used to determine charge-transport parameters in single-crystal and polycrystalline CVD diamond detectors. In the space-charge-limited regime, however, the time coordinate of a waveform feature cannot, in general, be identified directly with the physical carrier transient time. This work analyzes the conditions under which an extraction-feature time may be converted into a drift transit time by means of a correction factor. We argue that the correction factor is not a universal constant for diamond detectors, but a configuration-dependent quantity governed by injected-charge density, optical absorption depth, pre-existing effective space charge, contact physics, surface termination, and polarization driven by trapping. These effects modify the internal electric field during the transit and shift commonly used timing markers, including cusp, kink, arrival-edge, and integrated-charge definitions. Treating the correction factor as a fixed numerical value may therefore introduce systematic errors in extracted mobilities, especially when the transient evolves from the space-charge-free to the space-charge-limited regime. We propose that mobility extraction from SCL-TCT waveforms should be based on explicitly defined timing markers, intensity-dependent diagnostic scans, and configuration-specific calibration through forward modelling or independently constrained field profiles. The analysis provides a practical framework for improving the reliability of transport-parameter extraction in diamond radiation detectors.