Influence of Generated Defects by Ar Implantation on the Thermoelectric Properties of ScN

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). These were identified as interstitial-type defect clusters and argon vacancy complexes. The insertion of these specific defects induces acceptor-type deep levels in the band gap, yielding a reduction in the free-carrier mobility. With a reduced electrical conductivity, the irradiated sample exhibited a higher Seebeck coefficient while 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 influence of defects in increasing phonon scattering. Subsequent high-temperature annealing at 1573 K leads to the progressive evolution of these defects: the initial clusters of interstitials evolved to the benefit of smaller clusters and the formation of bubbles. 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 ( k total ∼ 8.5 W·m –1 ·K –1 ). This study shows that 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.

Influence of Ge to the formation of defects in epitaxial Mg2Sn1−x Ge x thermoelectric thin films

“…This technique offers insights into the quantity and nature of point defects and vacancies, which is particularly beneficial for comprehending defects in TE materials. 15,41,42) Fundamentally, when a positron enters a material, it diffuses into the material and annihilates against an electron emitting γ-rays. By measuring the energy distribution of the annihilation γ-rays and the lifetime of positrons in the material, vacancy-type defects can be detected.…”

“…14) Certain defects can also be introduced intentionally, especially after the material has been exposed to irradiation, implantation, or plastic deformation. 15,16) Doping and alloying stand as fundamental approaches for introducing defects, while alternative methods encompass electron irradiation, plasma treatment, and ion implantation. 6) The introduction of defects can enhance TE performance by reducing lattice thermal conductivity through additional phonon scattering by lattice defects.…”

Cathodoluminescence Characterization of Point Defects Generated through Ion Implantations in 4H-SiC

“…For this study, successive ion implantations of the samples were performed in order to form a homogeneous doped film and enable the formation of dopant-related point defects and defect complexes within the silicon carbide layer. The implantations were performed using three different ion beam facilities in France [18][19][20]. The dopants were nitrogen (N) and aluminum (Al).…”

Demonstration of compensated n-type scandium nitride Schottky diodes

“…However, the thermal conductivity of ScN (∼15 W mK −1 at 300 • C) is rather high that results in an overall moderate thermoelectric figure-of-merit (zT) of ∼0.15-0.30 at 500 • C [18,25]. Several strategies, such as alloying ScN with other heavy metal nitrides (such as NbN, CrN, etc) and ion-beam irradiation have been employed to reduce the thermal conductivity and increase ZT [26][27][28][29][30]. Solid solution alloys of ScN with wurtzite IIInitride semiconductors such as Al x Sc 1−x N, Ga x Sc 1−x N have also demonstrated high c-axis piezoelectric coefficient and are actively researched for resonators and bulk/surface acoustic wave devices in recent times [31][32][33][34].…”