# Acceptor levels of the carbon vacancy in $4H$-SiC: combining Laplace deep level transient spectroscopy with density functional modeling

## TL;DR

This study combines deep level transient spectroscopy and density functional modeling to identify and characterize the acceptor levels of carbon vacancies in 4H-SiC, revealing their electronic properties and transition sequences.

## Contribution

It provides direct experimental evidence and theoretical analysis of the acceptor levels of carbon vacancies in 4H-SiC, including their activation energies and transition sequences, which were previously not fully understood.

## Key findings

- Identified two components of the Z_{1/2} peak with specific activation energies.
- Assigned these components to acceptor levels of carbon vacancies at different lattice sites.
- Determined the positions of the first and second acceptor levels and their occupancy levels.

## Abstract

We provide direct evidence that the broad Z$_{1/2}$ peak, commonly observed by conventional DLTS in as-grown and at high concentrations in radiation damaged $4H$-SiC, has two components, namely Z$_{1}$ and Z$_{2}$, with activation energies for electron emission of 0.59 and 0.67~eV, respectively. We assign these components to $\mathrm{Z}_{1/2}^{=}\rightarrow\mathrm{Z}_{1/2}^{-}+e^{-}\rightarrow\mathrm{Z}_{1/2}^{0}+2e^{-}$ transition sequences from negative-$U$ ordered acceptor levels of carbon vacancy (V$_{\mathrm{C}}$) defects at hexagonal/pseudo-cubic sites, respectively. By employing short filling pulses at lower temperatures, we were able to characterize the first acceptor level of V$_{\mathrm{C}}$ on both sub-lattice sites. Activation energies for electron emission of 0.48 and 0.41~eV were determined for $\mathrm{Z}_{1}(-/0)$ and $\mathrm{Z}_{2}(-/0)$ transitions, respectively. Based on trap filling kinetics and capture barrier calculations, we investigated the two-step transitions from neutral to doubly negatively charged Z$_{1}$ and Z$_{2}$. Positions of the first and second acceptor levels of V$_{\mathrm{C}}$ at both lattice sites, as well as $(=\!/0)$ occupancy levels were derived from the analysis of the emission and capture data.