Multiphonon Theory of Electronic Transitions at Defects in Semiconductors -- Carrier Capture and Hydrogen Release

Abstract

Semiconductor devices make up all of modern electronics, so it is necessary to understand and model the degradation processes that cause reliability issues. Defects, such as Ga vacancies in GaN-based HEMTs, exist in these devices, but they are hydrogenated in the fabrication process, making them neutral and without a level in the gap to capture carriers. Highly-energetic (hot) carriers and multiple hits from colder carriers can transfer energy to the defect and cause hydrogen to be released. Dehydrogenated defects are considered active as they are often charged and can scatter or capture carriers. In prior work, the activation probability has been examined through a defect-activation cross section that was assumed to be a step function with a minimum activation energy. No work has previously been done from first-principles to find the defect activation rate, which is related to the rate of carrier scattering from a defect, but there has been extensive work on the specific case of scattering where the carrier loses all of its energy and is captured by the defect. However, prior applications of the capture theory were limited by considering energy dissipation into a single phonon mode because there is an exploding number of possible phonon configurations as more modes are allowed to participate. This work presents the revamped approach to the capture problem and a comparison to previous results and experiments. We then generalize the capture case to scattering between band states and present an algorithm that converts the carrier scattering rate to a hydrogen release rate. We present of proof-of-concept calculation for hole scattering and H release from a singly-hydrogenated Ga vacancy in GaN. We show that our methodology can predict the mean time before H release, which links directly with a model that gives the fraction of activated defects over time. We also show how the rates for different temperatures follow the Arrhenius equation, which can be used to fit our predicted rates to get the release attempt rate and an effective activation barrier for release.