Effect of ion-implantation-induced defects and Mg dopants on the thermoelectric properties of ScN

Abstract

For applications in energy harvesting, environmentally friendly cooling, and as power sources in remote or portable applications, it is desired to enhance the efficiency of thermoelectric materials. One strategy consists of reducing the thermal conductivity while increasing or retaining the thermoelectric power factor. An approach to achieve this is doping to enhance the Seebeck coefficient and electrical conductivity, while simultaneously introducing defects in the materials to increase phonon scattering. Here, we use Mg ion implantation to induce defects in epitaxial ScN (111) films. The films were implanted with Mg + ions with different concentration profiles along the thickness of the film, incorporating 0.35 to 2.2 at.% of Mg in ScN. Implantation at high temperature (600 ˚C), with few defects due to the temperature, does not substantially affect the thermal conductivity compared to a reference ScN. Samples implanted at room temperature, in contrast, exhibited a reduction of the thermal conductivity by a factor of three. The sample doped with 2.2 at.% Mg also showed an increased power factor after implantation. This study thus shows the effect of ion-induced defects on thermal conductivity of ScN films. High-temperature implantation allows the defects to be annealed out during implantation, while the defects are retained for room-temperature implanted samples, allowing for a drastic reduction in thermal conductivity.

The Effect of Point Defects on the Electronic Density of States of ScMN2-Type (M = V, Nb, Ta) Phases

“…It has also been shown that the Fermi level shifts towards the conduction band when the materials are doped with O. A study with Mg ion implantation with higher oxygen content retained n-type behavior [43]. Furthermore, it was noted in Figure 1c,d, Figure 2c,d, and Figure 3c,d that the highest occupied state is shifted into the conduction band in ScTaN 2 , ScNbN 2 , and ScVN 2 .…”

“…A study with Mg ion implantation with higher oxygen content retained n-type behavior. [43] Furthermore, it was noted in Figures 1c,d, 2c,d, and 3c,d that the highest occupied state is shifted into the conduction band in In terms of the transport distribution function, it has been theoretically shown that for a given lattice thermal conductivity, ZT is maximized when the transport distribution function consists of a Dirac delta function just above or below the Fermi level [41]. This is an idealized situation that does not correspond to real materials, but still a narrow distribution around the Fermi level will increase ZT [41,42].…”

Formation mechanism and thermoelectric properties of CaMnO3 thin films synthesized by annealing of Ca0.5Mn0.5O films

“…Finally, the amplitude and phase experimental profiles were fitted according to a standard Fourier diffusion law to extract the thermal conductivity of the CaMnO 3 films [25][26][27][28]. More details on the procedure of fit and extraction of the thermal conductivity of the film with a low thermal conductivity layer in between the gold and sapphire substrate can be found elsewhere [29].…”

High-throughput physical vapour deposition flexible thermoelectric generators

“…(2). This can be done by discovering new materials or optimising existing ones through techniques such as alloying or doping, where doping can also be used to tune the semiconductor type 9–11 .In the commercial world, roll-to-roll (R2R) systems are used to create large areas of high-throughput flexible coatings, and can be used to manufacture flexible electronics. Rolls of flexible materials, referred to as a web, are gradually unwound, coated and rewound, with the coated processes potentially consisting of multiple steps/layers.…”