The Effect of Substitution of Gallium on the Transport Properties of Polycrystalline GeTe

Abstract

We have investigated the electron transport properties of polycrystalline Ge1−xGaxTe alloys. Ga‐incorporation in GeTe has a nonmonotonic effect on its electrical conductivity which decreases slightly at low doping levels, but significantly at high doping levels (x ≥ 0.06) due to a concomitant reduction of hole‐concentration and mobility. Plausible Ga‐doping mechanisms determining these trends have been discussed. The Seebeck coefficient of GeTe does not enhance with Ga content as much as with Sb, Bi or In content at similar hole‐concentrations. Based on the theoretical Pisarenko plots and estimated effective carrier masses in Ge1−xGaxTe alloys, the observed behavior of Seebeck coefficient is rationalized on the basis of relative orbital energies and energy difference between valence band valleys in GeTe.

Boosting Thermoelectric Performance in Epitaxial GeTe Film/Si by Domain Engineering and Point Defect Control

“…The lower p value of the L-sample is likely attributed to the reduction of the V Ge , which comes from the film growth under the situation that Te is easily volatilized. As shown in Figure a, the L-sample exhibited relatively high μ comparable to polycrystalline GeTe bulks ,,,− at almost the same p , and higher μ than that of the polycrystalline GeTe thin films . Therefore, the L-sample exhibited almost the same σ tendency against p as polycrystalline GeTe bulks unlike polycrystalline GeTe films (Figure b).…”

“…We also measured the electrical properties of the L-sample. Figure a–c shows μ, σ, and S as a function of p at 300 K, respectively, where the data from the preceding studies were also plotted simultaneously. ,,,− The average p value of the L-sample was ∼3 × 10 20 cm –3 , which was lower than those of polycrystalline GeTe bulks (∼4–9 × 10 20 cm –3 ) ,,− and polycrystalline GeTe thin films (∼1–3 × 10 21 cm –3 ) . Furthermore, this p value was lower than or comparable to those of polycrystalline GeTe bulks containing an extra number of Ge (∼3–5 × 10 20 cm –3 ) .…”

“…(a–c) μ (a), σ (b), and S (c) of epitaxial GeTe thin films (Epi-film) as a function of p at 300 K. The preceding results of polycrystalline GeTe bulks (Bulk), polycrystalline GeTe thin films (Poly-film), and polycrystalline GeTe bulks containing an extra number of Ge (Bulk (extra Ge)) are also plotted simultaneously. ,,,− The broken line in (c) is the calculated S curve with acoustic phonon or grain boundary scatterings. (d) μ nor of epitaxial GeTe thin film as a function of T , where preceding results of polycrystalline GeTe thin films are also plotted simultaneously .…”

“…Because the extra amount of p was decreased, the L-sample exhibited higher S than polycrystalline GeTe bulks ,,,− and polycrystalline GeTe thin films (Figure c). S values of the L-sample decreased with the increase in p as well as those of the preceding studies. ,,,− We calculated theoretical p – S curves based on the Boltzmann transport theory under relaxation time and single parabolic band approximations. Then, the density-of-states effective mass m d is an important parameter for the analysis of TE properties .…”