Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userBand structure of a IV-VI black phosphorus analogue, the thermoelectric SnSe
102
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The success of black phosphorus in fast electronic and photonic devices is hindered by its rapid degradation in presence of oxygen. Orthorhombic tin selenide is a representative of group IV-VI binary compounds that are robust, isoelectronic, and share the same structure with black phosphorus. We measured the band structure of SnSe and found highly anisotropic valence bands that form several valleys having fast dispersion within the layers and negligible dispersion across. This is exactly the band structure desired for efficient thermoelectric generation where SnSe has shown a great promise.
rate research
Read More
IV-VI semiconductor SnSe has been known as the material with record high thermoelectric performance.The multiple close-to-degenerate valence bands in the electronic band structure has been one of the key factors contributing to the high power factor and thus figure of merit in the SnSe single crystal. To date, there have been primarily theoretical calculations of this particular electronic band structure. In this paper, however, using angle-resolved photoemission spectroscopy, we perform a systematic investigation of the electronic structure of SnSe. We directly observe three predicted hole bands with small energy differences between their band tops and relatively small in-plane effective masses, in good agreement with the ab initio calculations and critical for the enhancement of the Seebeck coefficient while keeping high electrical conductivity. Our results reveal the complete band structure of SnSe and help to provide a deeper understanding of the electronic origin of the excellent thermoelectric performances in SnSe.
We systematically investigated the geometric, electronic and thermoelectric (TE) properties of bulk black phosphorus (BP) under strain. The hinge-like structure of BP brings unusual mechanical responses such as anisotropic Youngs modulus and negative Poissons ratio. A sensitive electronic structure of BP makes it transform among metal, direct and indirect semiconductors under strain. The maximal figure of merit $ZT$ of BP is found to be 0.72 at $800,mathrm{K}$ that could be enhanced to 0.87 by exerting an appropriate strain, revealing BP could be a potential medium-high temperature TE material. Such strain-induced enhancements of TE performance are often observed to occur at the boundary of the direct-indirect band gap transition, which can be attributed to the increase of degeneracy of energy valleys at the transition point. By comparing the structure of BP with SnSe, a family of potential TE materials with hinge-like structure are suggested. This study not only exposes various novel properties of BP under strain, but also proposes effective strategies to seek for better TE materials.
Synchrotron-based angle-resolved photoemission spectroscopy is used to determine the electronic structure of layered SnSe, which was recently turned out to be a potential thermoelectric material. We observe that the top of the valence band consists of two nearly independent hole bands, whose tops differ by ~20 meV in energy, indicating the necessity of a multivalley model to describe the thermoelectric properties. The estimated effective masses are anisotropic, with in-plane values of 0.16-0.39 m$_0$ and an out-of-plane value of 0.71 m$_0$, where m$_0$ is the rest electron mass. Information of the electronic structure is essential to further enhance the thermoelectric performance of hole-doped SnSe.
Two-dimensional layered semiconductor black phosphorus (BP), a promising pressure induced Dirac system as predicted by band structure calculations, has been studied by $^{31}$P-nuclear magnetic resonance. Band calculations have been also carried out to estimate the density of states $D(E)$. The temperature and pressure dependences of nuclear spin lattice relaxation rate $1/T_1$ in the semiconducting phase are well reproduced using the derived $D(E)$, and the resultant pressure dependence of semiconducting gap is in good accordance with previous reports, giving a good confirmation that the band calculation on BP is fairly reliable. The present analysis of $1/T_1$ data with the complemental theoretical calculations allows us to extract essential information, such as the pressure dependences of $D(E)$ and chemical potential, as well as to decompose observed $1/T_1$ into intrinsic and extrinsic contributions. An abrupt increase in $1/T_1$ at 1.63GPa indicates that the semiconducting gap closes, resulting in an enhancement of conductivity.
We present results of electronic band structure, Fermi surface and electron transport properties calculations in orthorhombic $n$- and $p$-type SnSe, applying Korringa-Kohn-Rostoker method and Boltzmann transport approach. The analysis accounted for temperature effect on crystallographic parameters in $Pnma$ structure as well as the phase transition to $CmCm$ structure at $T_csim 807 $K. Remarkable modifications of conduction and valence bands were notified upon varying crystallographic parameters within the structure before $T_c$, while the phase transition mostly leads to jump in the band gap value. The diagonal components of kinetic parameter tensors (velocity, effective mass) and resulting transport quantity tensors (electrical conductivity $sigma$, thermopower $S$ and power factor PF) were computed in wide range of temperature ($15-900 $K) and, hole ($p-$type) and electron ($n-$type) concentration ($10^{17}-10^{21}$ cm$^{-3}$). SnSe is shown to have strong anisotropy of the electron transport properties for both types of charge conductivity, as expected for the layered structure. In general, $p$-type effective masses are larger than $n$-type ones. Interestingly, $p$-type SnSe has strongly non-parabolic dispersion relations, with the pudding-mold-like shape of the highest valence band. The analysis of $sigma$, $S$ and PF tensors indicates, that the inter-layer electron transport is beneficial for thermoelectric performance in $n$-type SnSe, while this direction is blocked in $p$-type SnSe, where in-plane transport is preferred. Our results predict, that $n$-type SnSe is potentially even better thermoelectric material than $p$-type one. Theoretical results are compared with single crystal $p$-SnSe measurements, and good agreement is found.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
