Radiation-Induced Charge Collection Comparison Between Silicon and Silicon Carbide Avalanche Photodiodes

Abstract

Avalanche photodiodes (APDs) are essential to multimessenger astronomy (MMA) space-based observatories for detecting low-intensity signals across the electromagnetic spectrum, often paired with scintillators for particle detection. However, the harsh radiation environment of space threatens to mask or imitate legitimate signals via single-event transients (SETs). This work investigates charge collection from 3.4 MeV alpha-induced SETs in Si and 4H-SiC APDs, which exhibit vastly different behavior. Relative to 0 V, the Si-APD shows suppressed gain (1.5x) while the SiC-APD shows significant gain (17x) near electrical breakdown. Calibrated Sentaurus TCAD simulations of both alpha strikes and optical generation reveal that both devices develop substantial space charge perturbations along the ion track, but only the Si-APD shows a corresponding collapse of the electric field and suppression of impact ionization in the avalanche region. We attribute this difference to device geometry. In the Si-APD, the ion track overlaps the high-field avalanche region, driving the local field collapse. In the SiC-APD, the higher epitaxial region doping confines the avalanche region to a micrometer-thin layer, leaving the high field relatively undisturbed. Holes then reach the avalanche region as a low-density, distributed flux that resembles optically-generated carriers. These results clarify differences in the radiation response of Si and SiC-APDs for future space-based observatory applications.