Negative thermal expansion coefficient and amorphization in defective 4H-SiC

TL;DR

This study investigates how defect accumulation in 4H-SiC affects its thermal properties, revealing a transition to negative thermal expansion and amorphization at critical defect densities through molecular dynamics simulations.

Contribution

It provides new insights into the effects of displacement damage on 4H-SiC's thermal behavior, highlighting the formation of amorphous clusters and negative thermal expansion at specific defect concentrations.

Findings

Negative thermal expansion occurs at critical defect densities.

Amorphous defect clusters form, causing macroscopic negative expansion.

Specific heat capacity decreases exponentially with increasing defect density.

Abstract

Silicon Carbide (SiC) is a wide bandgap semiconductor material recently being used in replacement of traditional semiconductors for high-voltage power device applications. Radiation environments induce defects through displacement damage in the lattice that can saturate over periods of high energy particle exposure at various concentrations. Defects are characterized by the formation of vacancies, interstitials and Frenkel pairs. Using molecular dynamics software we calculate thermal expansion coefficient (TEC) over and specific heat capacity at constant volume ($c_v$) values over a temperature range varying defect concentrations in single crystal 4H-SiC. At a discovered critical defect density amorphous defect clusters form in the lattice triggering macroscopic negative thermal expansion across the entire temperature range. Exponential $c_v$ loss is observed as defect density increases until the isothermal process becomes completely adiabatic at a identified critical Frenkel pair concentration. Providing insight to the degradation of SiC from displacement damage effects can ultimately assist the development of radiation-hardened electronics.