Excitation properties of the divacancy in 4H-SiC

TL;DR

This study combines experimental and theoretical approaches to understand the excitation-dependent quenching of photoluminescence in divacancies of 4H-SiC, revealing charge state conversions and trap-related effects.

Contribution

It provides a detailed analysis linking PL quenching thresholds to charge transfer levels and trap states in 4H-SiC divacancies, supported by ab initio calculations and EPR measurements.

Findings

PL quenching occurs below specific photon energy thresholds for different divacancy configurations.

The (0/-) charge transfer level aligns with the observed PL decay thresholds.

A simple model explains the charge state conversion and trap involvement in PL decay.

Abstract

We investigate the quenching of the photoluminescence (PL) from the divacancy defect in 4H-SiC consisting of a nearest-neighbour silicon and carbon vacancies. The quenching occurs only when the PL is excited below certain photon energies (thresholds), which differ for the four different inequivalent divacancy configurations in 4H-SiC. Refined theoretical ab initio calculation for the charge-transfer levels of the divacancy show very good agreement between the position of the (0/-) level with respect to the conduction band for each divacancy configurations and the corresponding experimentally observed threshold, allowing us to associate the PL decay with conversion of the divacancy from neutral to negative charge state due to capture of electrons photoionized from other defects (traps) by the excitation. Electron paramagnetic resonance measurements are conducted in dark and under excitation similar to that used in the PL experiments and shed light on the possible origin of traps in the different samples. A simple model built on this concept agrees well with the experimentally-observed decay curves.