Theory of the Thermal Stability of Silicon Vacancies and Interstitials in 4H–SiC

José Coutinho

doi:10.3390/cryst11020167

Abstract

This paper presents a theoretical study of the electronic and dynamic properties of silicon vacancies and self-interstitials in 4H–SiC using hybrid density functional methods. Several pending issues, mostly related to the thermal stability of this defect, are addressed. The silicon site vacancy and the carbon-related antisite-vacancy (CAV) pair are interpreted as a unique and bistable defect. It possesses a metastable negative-U neutral state, which “disproportionates” into VSi+ or VSi−, depending on the location of the Fermi level. The vacancy introduces a (−/+) transition, calculated at Ec−1.25 eV, which determines a temperature threshold for the annealing of VSi into CAV in n-type material due to a Fermi level crossing effect. Analysis of a configuration coordinate diagram allows us to conclude that VSi anneals out in two stages—at low temperatures (T≲600 °C) via capture of a mobile species (e.g., self-interstitials) and at higher temperatures (T≳1200 °C) via dissociation into VC and CSi defects. The Si interstitial (Sii) is also a negative-U defect, with metastable q=+1 and q=+3 states. These are the only paramagnetic states of the defect, and maybe that explains why it escaped detection, even in p-type material where the migration barriers are at least 2.7 eV high.

Highlights

Thermal Stability of Silicon VacanciesSilicon carbide (SiC) is currently a mature semiconductor that supports a variety of technologies, most notably in power electronics [1,2]
A defect state is referred to as S D q ( R), where D stands for a stoichiometric label (VSi or Si interstitial (Sii) for a silicon atom subtracted or added to a perfect crystal, respectively), q = {· · ·, −1, 0, +1, · · ·} is a charge state, S = {0, 1/2, 1, · · ·} the total spin
This paper presents a theoretical study of the transformation and migration mechanisms of Si vacancies and self-interstitials in 4H–Silicon VacanciesSilicon carbide (SiC) using first-principles methods

Summary

Introduction

Thermal Stability of Silicon VacanciesSilicon carbide (SiC) is currently a mature semiconductor that supports a variety of technologies, most notably in power electronics [1,2]. Intrinsic defects in SiC have recently received much attention from the community for their negative effects on device performance and for their promising role as building blocks in quantum technologies (e.g., quantum-bit holders, single-photon emitters, or quantumsensors) [3,4]. Most of these centers involve vacancies; they are usually introduced via electron or ion irradiation, and a precise understanding of their electronic and dynamic properties is of utmost importance, for instance, in order to control their positioning upon dynamic and thermal annealing treatments. Due to the extreme radiation hardness and the low leakage current of SiC junctions, this material has been proposed for the fabrication of radiation detectors [5,6], including neutrons [7], allowing for operation under harsh conditions, for instance, at high temperatures and under intense radiation fields [8]

Results

Discussion

Conclusion