Effects of Energetic Ion Strikes in Wide-Gap Semiconductors

Irradiation of semiconductors by energetic beams, including X-rays, lasers, and ion strikes, generates excess electrons and holes and may lead to device degradation or total failure. Depending upon the precise beam energetics and fluences, gradual degradation through total ionizing dose (TID) or sudden degradation/failure (i.e., soft and hard breakdowns) may occur. Wide-band-gap compound semiconductors are needed in power electronics where large voltages are applied to devices. However, the combination of single energetic heavy ions and large electric fields can lead to catastrophic device failure (i.e., single-event effects or SEE, including burnout and gate rupture). Although the role of defect dynamics at the atomic scale for TID effects have been adequately understood through combined experimental and density-functional theory (DFT) calculations, comparatively little has been done to document the role for ion-induced defects in SEE. It has been observed that single energetic ions in wide-gap-semiconductor power devices under large reverse voltages induce sudden large leakage-current jumps that remain intact after the ion is gone, a phenomenon that is known as single-event leakage current (SELC). The persistence of the current suggests that some defect-mediated process may be establishing stable conducting paths. At even higher voltages, an energetic ion can cause a catastrophic sudden rise of the current leading to burnout, that is usually attributed to an intense “electron plasma channel” along the ion path. In this talk, we will begin with a short review of the literature including a discussion of recent experiments on SEE in β-Ga₂O₃ [1]. These experiments, in particular, the observed progressive jumps in leakage current and eventual device failure, during ion-irradiation serve to motivate our theoretical modeling. We begin the discussion of our proof-of-principle DFT calculations in a model cubic GaN system for two defect-related excess-carrier phenomena [2]. First, we document the existence, dynamics, and role of quasi-localized “resonant states” in the energy-band continua that form as a result of the defects and their motion. An increase in the number of these states may enhance TID-excess-carrier and hot-carrier degradation as they evolve and multiply during energetic-ion-induced atom recoils and defect creation (displacement damage) and can potentially serve as excess-carrier conduction paths in SEE. The second phenomenon is the conversion of isolated vacancies into nanovoids by large voltages that can generate sufficient Joule heating to overcome the pertinent energy barriers and cause explosive SEE burnouts (hard breakdowns). More recently, the group has recognized that SELC can be caused by a novel process by which available Joule heating, lower than is necessary for void growth, leads to the formation of conducting anion-vacancy chains (vacancy nanowires). The energetics of the formation of such nanowires is used to rate the robustness of different wide-band-gap semiconductors to SELC.

[1] R. M. Cadena, et al. “Low-energy ion-induced single-event burnout in gallium oxide Schottky diodes,” IEEE Tran. Nucl. Sci. 70, 363 (2023).
[2] A. O’Hara, et al. “Defect dynamics in the presence of excess energetic carriers and high electric field in wide-gap semiconductors,” J. Appl. Phys. 135, (2024).