Mechanism of $E'_\gamma$ Defect Generation in Ionizing-irradiated $a$-SiO$_2$: The Nonradiative Carrier Capture-Structural Relaxation Model

Abstract

The total ionizing dose (TID) effect of semiconductor devices stems from radiation-induced $E'_\gamma$ defects in the $a$-SiO$_2$ dielectrics, but the conventional ``hole transport-trapping'' model of defect generation fails to explain recent basic experiments. Here, we propose an essentially new ``nonradiative carrier capture-structural relaxation'' (NCCSR) mechanism that can consistently explain the puzzling temperature/electric-field dependence, based on spin-polarized HSE06 hybrid functional calculations and existing experimental alignment of defect formation energies and charge capture cross-sections of large-sample oxygen vacancies in $a$-SiO$_2$. It is revealed that, the long-assumed $V_{O\gamma}$ precursors with high formation energy cannot survive in high temperature-grown $a$-SiO$_2$; whereas the stable $V_{O\delta}$ can capture irradiation-induced holes via strong electron-phonon coupling, generating metastable $E'_\delta$ that most relax into stable $E'_\gamma$. A fractional power-law (FPL) dynamic model is derived based on the mechanism and the Kohlrausch-Williams Watts (KWW) decay function. It can uniformly describe nonlinear data over a wide dose and temperature range. This work not only provides a solid cornerstone for prediction and hardening of TID effects of SiO$_2$-based semiconductor devices, but also offers a general approach for studying ionizing radiation physics in alternative dielectrics with intrinsic electronic metastability and dispersion.