Search query: SnSe degenerate semiconductor

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abstract: We have studied the electronic structure of SnSe and Na doped SnSe by means of angle resolved photoemission spectroscopy. The valence band top reaches the Fermi level by the Na doping, indicating that Na doped SnSe can be viewed as a degenerate semiconductor. However, in the Na doped system, the chemical potential shift with temperature is unexpectedly large and is apparently inconsistent with the degenerate semiconductor picture. The large chemical potential shift and anomalous spectral shape are key ingredients for an understanding of the novel metallic state with the large thermoelectric performance in Na doped SnSe.
author_names: Makoto Maeda

K Yamamoto

Takashi Mizokawa

Naurang Lal Saini

Masashi Arita

Hirofumi Namatame

Masaki Taniguchi

Gangjian Tan

Li-dong Zhao

Mercouri G Kanatzidis
title: Unusually large chemical potential shift in a degenerate semiconductor: Angle resolved photoemission study of SnSe and Na doped SnSe
year: 2018

abstract: IV VI semiconductor SnSe has been known as the material with record high thermoelectric performance. The multiple close to degenerate (or "convergent" 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.
author_names: Chunwu Wang

Y Y Xia

Zhen Tian

J Jiang

B H Li

Shengtao Cui

H F Yang

A J Liang

X Y Zhan

G H Hong

Shiyang Liu

Changyong Chen

M X Wang

L X Yang

Zhi Liu

Qixi Mi

G Li

Jiang Xue

Zeheng Liu

Yu Chen
title: Photoemission study of the electronic structure of valence band convergent SnSe
year: 2017

abstract: The approximate maximum figure of merit as calculated by Joffe, zJ (4k2q)(ml) erNv, may be rewritten as zJ (2keq)2(sl)exp(qak) where a and s are the Seebeck coefficient and electrical conductivity of any non degenerate and extrinsic sample of the semiconductor investigated; l is the lattice thermal conductivity. The second equation makes it possible to evaluate zJ easily and without knowledge of the values of the scattering parameter r and the effective density of states Nv. In an Appendix it is shown that the rigorously calculated maximum of the dimensionless figure of merit zT is mainly a function of zJT. Room temperature values of zJT are given for p type mixed crystals of SnS and SnSe. From 0*28 for SnS zJT rapidly decreases to about 0*14 for SnS0*6Se0*4 and then slowly increases to 0*15 for SnSe.
author_names: J D Wasscher

Walter A Albers

C Haas
title: Simple evaluation of the maximum thermoelectric figure of merit, with application to mixed crystals SnS1 xSex
year: 1963

abstract: Abstract There had been tremendous growth in the field of Integrated circuits (ICs) in the past fifty years. Scaling laws mandated both lateral and vertical dimensions to be reduced and a steady increase in doping densities. Most of the modern semiconductor devices have invariably heavily doped regions where Fermi Dirac Integrals are required. Several attempts have been devoted to developing analytical approximations for Fermi Dirac Integrals since numerical computations of Fermi Dirac Integrals are difficult to use in semiconductor devices, although there are several highly accurate tabulated functions available. Most of these analytical expressions are not sufficiently suitable to be employed in semiconductor device applications due to their poor accuracy, the requirement of complicated calculations, and difficulties in differentiating and integrating. A new approximation has been developed for the Fermi Dirac integrals of the order 1/2 by using Prony's method and discussed in this paper. The approximation is accurate enough (Mean Absolute Error (MAE) 0.38% and easy enough to be used in semiconductor device equations. The new approximation of Fermi Dirac Integrals is applied to a more generalized Einstein Relation which is an important relation in semiconductor devices.
author_names: Ahmed Alqurashi

Chettypalayam R Selvakumar
title: A new approximation of Fermi Dirac integrals of order 1/2 for degenerate semiconductor devices
year: 2018

abstract: Abstract The phonon growth characteristic in a degenerate semiconductor has been calculated under the condition of low temperature. If the lattice temperature is high, the energy of the intravalley acoustic phonon is negligibly small compared to the average thermal energy of the electrons. Hence one can traditionally assume the electron phonon collisions to be elastic and approximate the Bose Einstein (B.E. distribution for the phonons by the simple equipartition law. However, in the present analysis at the low lattice temperatures, the interaction of the non equilibrium electrons with the acoustic phonons becomes inelastic and the simple equipartition law for the phonon distribution is not valid. Hence the analysis is made taking into account the inelastic collisions and the complete form of the B.E. distribution. The high field distribution function of the carriers given by Fermi Dirac (F.D. function at the field dependent carrier temperature, has been approximated by a well tested model that apparently overcomes the intrinsic problem of correct evaluation of the integrals involving the product and powers of the Fermi function. Hence the results thus obtained are more reliable compared to the rough estimation that one may obtain from using the exact F.D. function, but taking recourse to some over simplified approximations.
author_names: A N Basu

Bimalendu Das

Tapas Ranjan Middya

D P Bhattacharya
title: A realistic analysis of the phonon growth characteristics in a degenerate semiconductor using a simplified model of Fermi Dirac distribution
year: 2017

abstract: Two dimensional (2D) crystals have emerged as a class of materials with tunable carrier density1. Carrier doping to 2D semiconductors can be used to modulate many body interactions2 and to explore novel composite particles. The Holstein polaron is a small composite particle of an electron that carries a cloud of self induced lattice deformation (or phonons)3 5, which has been proposed to play a key role in high temperature superconductivity6 and carrier mobility in devices7. Here we report the discovery of Holstein polarons in a surface doped layered semiconductor, MoS2, in which a puzzling 2D superconducting dome with the critical temperature of 12 K was found recently8 11. Using a high resolution band mapping of charge carriers, we found strong band renormalizations collectively identified as a hitherto unobserved spectral function of Holstein polarons12 18. The short range nature of electron phonon (e ph) coupling in MoS2 can be explained by its valley degeneracy, which enables strong intervalley coupling mediated by acoustic phonons. The coupling strength is found to increase gradually along the superconducting dome up to the intermediate regime, which suggests a bipolaronic pairing in the 2D superconductivity.A high resolution ARPES study on electron doped MoS2 reveals strong band renormalization effects near the conduction band minima, which are interpreted in terms of Holstein type electron phonon interactions.
author_names: Mingu Kang

S W Jung

Woo Jong Shin

Yeongsup Sohn

Sae Hee Ryu

Timur K Kim

Moritz Hoesch

Keun Su Kim
title: Holstein polaron in a valley degenerate two dimensional semiconductor
venue: Nature Materials
year: 2018

abstract: We present an optoelectronic switch for functional plasmonic circuits based on active control of Surface Plasmon Polaritons (SPPs) at degenerate PN+ junction interfaces. Self consistent multi physics simulations of the electromagnetic, thermal and IV characteristics of the device have been performed. The lattice matched Indium Gallium Arsenide (In0.53Ga0.47As) is identified as a better semiconductor material compared to Si for the practical implementation of the proposed optoelectronic switch providing higher optical confinement, reduced size and faster operation. The optimal device is shown to operate at signal modulation surpassing 100 dB, responsivity in excess of 600 dB*V 1 and switching rates up to 50 GHz, thus potentially providing a new pathway toward bridging the gap between electronic and photonic devices.
author_names: Raj K Vinnakota

Dentcho A Genov
title: Active Control of Charge Density Waves at Degenerate Semiconductor Interfaces
venue: Scientific Reports
year: 2017

abstract: We report on high performance transparent Al:ZnO (AZO) thin film heaters on flexible polymer (polyethylene terephthalate) and glass substrates which demonstrate low sheet resistivity. AZO thin films were grown by radio frequency magnetron sputtering at low Ts (below 200 degC) on flexible, transparent polyethylene terephthalate substrates that show stable and reproducible results by applying low <10 V) voltages. This study also examined identical AZO thin films on glass substrates that showed highly reproducible heating effects due to the Joule heating effect. The potential applications are foldable and wearable electronics, pain/injury therapy smart windows, automobile window defrosters, and low cost power electronics.
author_names: Monee K Roul

Brandon Obasogie

Gilbert Kogo

Jonathan Skuza

Rajeh Mundle

Aswini K Pradhan
title: Transparent and flexible heaters based on Al:ZnO degenerate semiconductor
year: 2017

abstract: Abstract As rechargeable lithium ion batteries (LIBs) develop unprecedentedly faster than ever before, it needs urgently to search for a new and careful design of anode materials, which can boost the battery performance substantially, particularly the rate capability, in order to realize fast charge and discharge in the practical applications of high energy devices. On that account, heterostructures with the excellent interface effects and the formation of built in potential at the hetero interface have emerged as a promising solution to address the above issue. In this paper, we prepared SnSe/SnO2@Gr heterostructure composite, in which the SnO2 nanospheres are homogeneously dispersed and wrapped into the Graphene matrix, interconnecting to form a three dimensional (3D) hierarchical architecture, followed by the selenium treatment to obtain SnSe/SnO2 heterostructure. This distinctive nanoarchitecture can enhance charge transfer and lithium ions diffusion, as well as improving specific conductivity and charge/discharge capability of SnSe/SnO2@Gr heterostructure. When used as anode material for lithium ion batteries, SnSe/SnO2@Gr shows a higher rate capability than SnO2@Gr and SnO2. Moreover, after 200 cycles, the storage capacity of SnSe/SnO2@Gr is still up to 810 mAh/g and almost remains unchanged, suggesting a high cyclability. It is noted that the enhanced electrochemical performance of SnSe/SnO2@Gr can be attributed to the built in electric field of heterojunction, which is proved by the DFT calculation and CI NEB methods, illustrating that the existence of the built in electric field adds an additional electromotive force (phE) to boost the electron mobility of the active material. Noteworthy, the results show that the large difference of the work function of the two semiconductor materials could lead to the high additional potential (phE) which surly be the beneficial for improving the performance of the battery.
author_names: Kai-Hong Chen

Xiujuan Wang

Gang Wang

Beibei Wang

Xiaojie Liu

Jintao Bai

Hui Wang
title: A new generation of high performance anode materials with semiconductor heterojunction structure of SnSe/SnO2@Gr in lithium ion batteries
year: 2018

abstract: SnSe, a group IV VI monochalcogenide with layered crystal structure similar to black phosphorus, has recently attracted extensive interests due to its excellent thermoelectric properties and potential device applications. Experimental electronic structure of both the valence and conduction bands is critical for understanding the effects of hole versus electron doping on the thermoelectric properties, and to further reveal possible change of the band gap upon doping. Here, we report the multivalley valence bands with a large effective mass on semiconducting SnSe crystals and reveal single valley conduction bands through electron doping to provide a complete picture of the thermoelectric physics. Moreover, by electron doping through potassium deposition, the band gap of SnSe can be widely tuned from 1.2 eV to 0.4 eV, providing new opportunities for tunable electronic and optoelectronic devices.
author_names: Kenan Zhang

Ke Deng

Jiaheng Li

Haoxiong Zhang

Wei Yao

Jonathan D Denlinger

Yang Wu

Wenhui Duan

Shuyun Zhou
title: Widely tunable band gap in a multivalley semiconductor SnSe by potassium doping
year: 2018