Speaker
Description
The wide-bandgap semiconductor 4H-SiC offers radiation hardness, thermal stability and a high critical field, making it an attractive fast-timing detector material that can operate without cooling in harsh environments. To compensate for its low charge generation, the low-gain avalanche diode (LGAD) concept provides internal amplification, but device performance hinges on a narrow gain-layer implant whose batch-to-batch variability currently limits reproducibility.
We present TCAD work on 4H-SiC LGADs developed within the CAPADS programme together with onsemi, building on three generations of single-pad prototypes and extending toward segmented devices. A trustworthy device model was established by matching simulated and measured capacitance-voltage curves through the epitaxial concentration, epitaxial thickness and gain-layer dose, since the standard SiC TCAD models and low-concentration SIMS are insufficient on their own; this revealed significant gaps between nominal and effective fabrication parameters. With the calibrated model, two instabilities were identified: a strong sensitivity of gain to the gain-layer nitrogen dose, and aluminium dopant channelling that produces a parasitic secondary junction below the gain layer, highly dependent on implantation tilt. A change of implantation tilt from 0° to 5° is proposed to suppress the channelling tail and stabilise the gain, and verification wafers were fabricated and characterised. Building on this single-pad understanding, we report the first fabricated and characterised segmented 4H-SiC LGADs: strip detectors with 80 µm pitch and pixel arrays with 55 and 110 µm pitch, using inter-channel isolation strategies including geometric separation and oxide-filled trenches. Together these results advance both the reproducibility and the spatial segmentation of 4H-SiC LGADs.