Magnetron Deposition of In Situ Thermoelectric Mg2Ge Thin Films

Abstract

Thin films of the semiconducting compound Mg 2 Ge were deposited by magnetron cosputtering from source targets of high-purity Mg and Ge onto glass substrates at temperatures T s = 300°C to 700°C. X-ray diffraction shows that the Mg 2 Ge compound begins to form at a substrate temperature T s % 300°C. Films deposited at T s = 400°C to 600°C are single-phase Mg 2 Ge and have strong x-ray peaks. At higher T s the films tend to be dominated by a Ge-rich phase primarily due to the loss of magnesium vapor from the condensing film. At optimum deposition temperatures, 550°C to 600°C, films have an electrical conductivity r 600 K = 20 X À1 cm À1 to 40 X À1 cm À1 and a Seebeck coefficient a = 300 lV K À1 to 450 lV K À1 over a broad temperature range of 200 K to 600 K.

Thermoelectric Properties of Ag-doped Mg2Ge Thin Films Prepared by Magnetron Sputtering

“…The electrical conductivity (Fig. 4) of the undoped Mg 2 Ge thin film was similar to that in our previous data, 8 and its temperature dependence was consistent with doped semiconductor behavior. The lower silver doping level caused a little change in conductivity, as expected from the measured carrier concentration.…”

“…8 We extended our work and here present the results of the p-type doping of Mg 2 Ge thin films. Successful Ag-doping was achieved in situ, where Ag atoms from a sacrificial base layer EXPERIMENT Thin films of Mg 2 Ge were deposited at a substrate temperature of 773 K by direct current (d.c.) magnetron co-sputtering of high-purity Mg (99.95%) and Ge (99.999%) targets in ultra-high purity Ar gas at a pressure of 1 Pa.…”

“…Details of the deposition apparatus and method can be found elsewhere. [8][9][10] For the study described here, the polished low-alkali glass substrates (10 9 10 9 1 mm 3 ) were fixed onto a heated substrate table with silver paste, achieving good thermal contact. Prior to film growth, a very thin sacrificial layer of silver was deposited onto the bare glass substrate and acted as a source of Ag dopant.…”

Anharmonic properties inMg2X(X=C,SiChernatynskiy1, Phillpot2 2015Phys. Rev. B18280View full textAdd to dashboardCite

“…4,7,48 From the electronic properties perspective, Mg 2 C, Mg 2 Si, Mg 2 Ge and Mg 2 Sn are all indirect gap semiconductors with decreasing gaps for the latter 3 compounds of 0.77, 0.74 and 0.34 eV. 49 Our DFT calculations predict smaller gaps of 0.13, 0.17 and 0.0 eV respectively, slightly smaller than the DFT-GGA data of 0.23, 0.17 and 0.0 eV reported previously. 12 Our result for Mg 2 C is 0.75 eV, slightly greater than DFT-PBE result of 0.67 eV reported in the literature.…”

Thermal Conductivity and Other Transport Properties of Mg2Sn:Ag Crystals

“…Recently, we began a comprehensive investigation of the preparation and properties of Mg 2 X (X = Sn, Si, Ge). [10][11][12] In this paper, we focus on Mg 2 Sn:Ag and report on the temperature dependence (T = 2 K to 400 K) of the thermal conductivity, electrical resistivity, and Seebeck coefficient as the addition of silver, a p-type dopant, is systematically increased in the range of Ag = 0 at.% to 1 at.%. In two companion papers we report on the role of microstructure on the thermoelectric properties 13 and on the density of states of the Ag impurity and the hole Fermi surface.…”