Influence of generated defects by Ar-implantation on the thermoelectric properties of ScN

TL;DR

This study demonstrates that argon ion implantation creates stable defects in ScN thin films, significantly reducing thermal conductivity and potentially enhancing thermoelectric efficiency through defect engineering.

Contribution

It introduces a method of defect engineering via argon ion implantation to improve thermoelectric properties of ScN by reducing thermal conductivity while maintaining electrical performance.

Findings

Thermal conductivity reduced from 12 to 3 W/m·K at 300 K.

Defects such as interstitial clusters and argon-vacancy complexes are stable up to 750 K.

Post-annealing partially restores electrical properties but retains reduced thermal conductivity.

Abstract

Nowadays, making thermoelectric materials more efficient in energy conversion is still a challenge. In this work, to reduce the thermal conductivity and thus improve the overall thermoelectric performances, point and extended defects were generated in epitaxial 111-ScN thin films by implantation using argon ions. The films were investigated by structural, optical, electrical, and thermoelectric characterization methods. The results demonstrated that argon implantation leads to the formation of stable defects (up to 750 K operating temperature) were identified as interstitial type defect clusters and so-called argon-vacancy complexes. The insertion of those specific defects induces acceptor-type deep levels in the bandgap yielding to a reduce of the free carrier mobility. With a reduce electrical conductivity, the irradiated sample exhibited higher Seebeck coefficient maintaining the power factor of the film. The thermal conductivity is strongly reduced from 12 to 3 W.m-1.K-1 at 300 K, showing the effect of defects in increasing phonon scattering. Subsequent high temperature annealing, at 1573 K, leads to the progressive evolution of defects: the initial clusters of interstitial evolved to the benefit of smaller clusters and the formation of bubble. Thus, the number of free carriers, the resistivity and the Seebeck coefficient are almost restored but the mobility of the carriers remains low and a 30% drop in thermal conductivity is still effective (8.5 W.m-1.K-1). This study shows that the control defect engineering with defects introduced by irradiation using noble gases in a thermoelectric coating can be an attractive method to enhance the figure of merit of thermoelectric materials.