The one-electron (Bethe-Sommerfeld) model of electron tunneling is formulated to describe tunneling when the curvature (electron mass) and centroid of the one-electron constant-energy surfaces vary across the junction. The conductance for an abrupt GaAs $p\ensuremath{-}n$ tunnel diode is calculated and shown to exhibit minima near zero bias for highly asymmetrical doping ratios. The conductance of metal-oxide-semimetal (M-O-SM) tunnel junctions is evaluated both with and without the inclusion of space-charge effects and of surface states. All calculations are performed using solvable models for which the WKBJ approximation is not imposed. Neither the removal of the WKBJ approximation nor the space-charge effects give rise to maxima in the conductance of the M-O-SM junctions near a band edge.

Space-Charge Effects on Electron Tunneling

From an environmental perspective, lead-free SnTe would be preferable for solid-state waste heat recovery if its thermoelectric figure-of-merit could be brought close to that of the lead-containing chalcogenides. In this work, we studied the thermoelectric properties of nanostructured SnTe with different dopants, and found indium-doped SnTe showed extraordinarily large Seebeck coefficients that cannot be explained properly by the conventional two-valence band model. We attributed this enhancement of Seebeck coefficients to resonant levels created by the indium impurities inside the valence band, supported by the first-principles simulations. This, together with the lower thermal conductivity resulting from the decreased grain size by ball milling and hot pressing, improved both the peak and average nondimensional figure-of-merit (ZT) significantly. A peak ZT of ∼1.1 was obtained in 0.25 atom % In-doped SnTe at about 873 K.

https://www.pnas.org/content/pnas/110/33/13261.full.pdf

High thermoelectric performance by resonant dopant indium in nanostructured SnTe

SnTe is a potentially attractive thermoelectric because it is the lead-free rock-salt analogue of PbTe. However, SnTe is a poor thermoelectric material because of its high hole concentration arising from inherent Sn vacancies in the lattice and its very high electrical and thermal conductivity. In this study, we demonstrate that SnTe-based materials can be controlled to become excellent thermoelectrics for power generation via the successful application of several key concepts that obviate the well-known disadvantages of SnTe. First, we show that Sn self-compensation can effectively reduce the Sn vacancies and decrease the hole carrier density. For example, a 3 mol % self-compensation of Sn results in a 50% improvement in the figure of merit ZT. In addition, we reveal that Cd, nominally isoelectronic with Sn, favorably impacts the electronic band structure by (a) diminishing the energy separation between the light-hole and heavy-hole valence bands in the material, leading to an enhanced Seebeck coefficien...

High Thermoelectric Performance of p-Type SnTe via a Synergistic Band Engineering and Nanostructuring Approach

We treat theoretically, through the use of Bloch functions, a new semiconductor superlattice where the interaction of the conduction band in one host material with the valence band of the other host material plays an important role. The result indicates that this superlattice offers new intriguing features, realizable with the In1−xGaxAs‐GaSb1−y Asy system. In addition, the tunneling probability is calculated across a barrier involving this system.

A new semiconductor superlattice

Conduction through thin dielectric films sandwiched between metal and semiconductor electrodes is reviewed.

https://iopscience.iop.org/article/10.1088/0022-3727/4/5/202/pdf

P. J. Stiles

Papers

New Type of Negative Resistance in Barrier Tunneling