Query: Charge scattering and mobility in atomically thin semiconductors

Candidate papers:

abstract: The electron transport properties of atomically thin semiconductors such as MoS2 have attracted significant recent scrutiny and controversy. In this work, the scattering mechanisms responsible for limiting the mobility of single layer semiconductors are evaluated. The roles of individual scattering rates are tracked as the 2D electron gas density is varied over orders of magnitude at various temperatures. From a comparative study of the individual scattering mechanisms, we conclude that all current reported values of mobilities in atomically thin transition metal dichalcogenide semiconductors are limited by ionized impurity scattering. When the charged impurity densities are reduced, remote optical phonon scattering will determine the ceiling of the highest mobilities attainable in these ultrathin materials at room temperature. The intrinsic mobilities will be accessible only in clean suspended layers, as is also the case for graphene. Based on the study, we identify the best choices for surrounding dielectrics that will help attain the highest mobilities.
author_names: N Ma

Debdeep Jena
title: Charge Scattering and Mobility in Atomically Thin Semiconductors
year: 2014

abstract: The transition metal dichalcogenides have attracted a lot of attention as a possible stepping stone toward atomically thin and flexible field effect transistors. One key parameter to describe the charge transport is the time between two successive scattering events the transport scattering time. In a recent report, we have shown that it is possible to use density functional theory to obtain the band structure of two dimensional semiconductors in presence of field effect doping. Here, we report a simple method to extract the scattering time from the experimental conductivity and from the knowledge of the band structure. We apply our approach to monolayers and multilayers of MoS$_2$ MoSe$_2$ MoTe$_2$ WS$_2$ and WSe$_2$ in presence of a gate. In WS$_2$ for which accurate measurements of mobility have been published, we find that the scattering time is inversely proportional to the density of states at the Fermi level. Finally, we show that it is possible to identify the critical doping at which different valleys start to be occupied from the doping dependence of the conductivity.
author_names: Thomas Brumme

Matteo Calandra

Francesco Mauri
title: Determination of scattering time and of valley occupation in transition metal dichalcogenides doped by field effect
year: 2016

abstract: Incorporation of tetramethylammonium iodide into conjugated D A polymer thin film leads to remarkable enhancement of charge mobility. Organic semiconductors with high charge carrier mobilities are crucial for flexible electronic applications. Apart from designing new conjugated frameworks, different strategies have been explored to increase charge carrier mobilities. We report a new and simple approach to enhancing the charge carrier mobility of DPP thieno[3,2 b]thiophene conjugated polymer by incorporating an ionic additive, tetramethylammonium iodide, without extra treatments into the polymer. The resulting thin films exhibit a very high hole mobility, which is higher by a factor of 24 than that of thin films without the ionic additive under the same conditions. On the basis of spectroscopic grazing incidence wide angle x ray scattering and atomic force microscopy studies as well as theoretical calculations, the remarkable enhancement of charge mobility upon addition of tetramethylammonium iodide is attributed primarily to an inhibition of the torsion of the alkyl side chains by the presence of the ionic species, facilitating a more ordered lamellar packing of the alkyl side chains and interchain p p interactions.
author_names: Hewei Luo

Chenmin Yu

Zitong Liu

Guanxin Zhang

Hua Geng

Yuanping Yi

Katharina Broch

Yuanyuan Hu

Aditya Sadhanala

Lang Jiang

Penglin Qi

Zhengxu Cai

Henning Sirringhaus

Deqing Zhang
title: Remarkable enhancement of charge carrier mobility of conjugated polymer field effect transistors upon incorporating an ionic additive
venue: Science Advances
year: 2016

abstract: Clean interface and low contact resistance are crucial requirements in two dimensional (2D) materials to preserve their intrinsic carrier mobility. However, atomically thin 2D materials are sensitive to undesired Coulomb scatterers such as surface/interface adsorbates, metal to semiconductor Schottky barrier (SB) and ionic charges in the gate oxides, which often limits the understanding of the charge scattering mechanism in 2D electronic systems. Here, we present the effects of hafnium dioxide (HfO2) high k passivation and SB height on the low frequency (LF) noise characteristics of multilayer molybdenum ditelluride (MoTe2) transistors. The passivated HfO2 passivation layer significantly suppresses the surface reaction and enhances dielectric screening effect, resulting in an excess electron n doping, zero hysteresis, and substantial improvement in carrier mobility. After the high k HfO2 passivation, the obtained LF noise data appropriately demonstrates the transition of the Coulomb scattering mechanism from the SB contact to the channel, revealing the significant SB noise contribution to the 1/f noise. The substantial excess LF noise in the subthreshold regime is mainly attributed to the excess metal to MoTe2 SB noise and is fully eliminated at the high drain bias regime. This study provides a clear insight into the origin of electronic signal perturbation in 2D electronic systems.
author_names: Min-Kyu Joo

Yoojoo Yun

Hyunjin Ji

Dongseok Suh
title: Coulomb scattering mechanism transition in 2D layered MoTe2: effect of high k passivation and Schottky barrier height.
venue: Nanotechnology
year: 2019

abstract: Simultaneously achieving higher carriers concentration and mobility is a technical challenge against up scaling the transparent conductive performances of transparent conductive oxides. Utilizing one order higher dense ~1 x 1011 cm 3) plasmas (in comparison to the conventional direct current plasmas) highly c axis oriented Al doped ZnO films have been prepared with precise control over relative composition and chemical states of constituting elements. Tailoring of intrinsic (O vacancies) and extrinsic (ionic Al and zero valent Al) dopants provide simultaneous enhancement in mobility and concentration of charge carriers. Room temperature resistivity as low as 4.89 x 10 4 O cm along the carrier concentration 5.6 x 1020 cm 3 is obtained in 200 nm thick transparent films. Here, the control of atomic Al reduces the charge trapping at grain boundaries and subdues the effects of grain boundary scattering. A mechanism based on the correlation between electron hole interaction and carrier mobility is proposed for degenerately doped wide band gap semiconductors.
author_names: Manish Kumar

Long Wen

Bibhuti Bhusan Sahu

Jeon Geon Han
title: Simultaneous enhancement of carrier mobility and concentration via tailoring of Al chemical states in Al ZnO thin films
year: 2015

abstract: In this work, we have applied the Airy Function Transfer Matrix Method to provide a numerical description of the charge scattering mechanisms taking place at the grain boundaries in polycrystalline, degenerately Al doped ZnO (ZnO:Al) films, one of the most studied Transparent Conductive Oxides (TCOs) By discretizing the potential barrier at the grain boundary into linear segments, an accurate calculation of the electron tunneling probability through the grain boundaries has been obtained. Conversely to analytical models based on the Wentzel Kramers Brillouin (WKB) approximation, our new approach is valid for any doping level. We thus provide a complete model that allows a comprehensive explanation of carrier transport in highly doped semiconductors, for which charge tunneling across grain boundaries cannot be neglected. We have tested our model with ZnO:Al thin films prepared by different physical and chemical deposition techniques, namely, sputtering, atomic layer deposition and atmospheric pressure spatial atomic layer deposition. A linear relationship between the trap density at the grain boundaries and carrier density has been extracted by fitting our model to Hall mobility data for the different samples. Our results provide guidance on how to adapt the deposition conditions to obtain high quality materials, with an optimum ratio between optical and electrical properties as required for specific applications.
author_names: V Nguyen

Ulrich Gottlieb

Anthony Valla

Delfina Munoz

Daniel Bellet

David Munoz-Rojas
title: Electron tunneling through grain boundaries in transparent conductive oxides and implications for electrical conductivity: the case of ZnO:Al thin films
year: 2018

abstract: High molecular symmetry is always observed in high performance organic semiconductors. However, whether it is an essential factor for molecular design is unclear. In this work, we designed and synthesized three quinoidal isomers, QBTT o, QBTT i, and QBTT s, with different sulfur orientations and a stable E configuration to investigate the relationship between the structure symmetry and organic thin film transistor performance. We found that QBTT o and QBTT i with high C2h symmetry exhibit electron mobilities of 0.02 and 0.15 cm2 V 1 s 1, respectively, while QBTT s exhibits an unexpectedly high electron mobility of 0.32 cm2 V 1 s 1 with Ion/Ioff ratios of =106. The enhanced electron mobilities from QBTT o and QBTT i to QBTT s can be attributed to the different sulfur orientations, especially, molecular symmetry. The thin film microstructures of three QBTTs were systematically investigated by grazing incidence wide angle X ray scattering, near edge X ray absorption fine structure spectroscopy, atomic force
author_names: Longbin Ren

Dafei Yuan

Eliot Gann

Yuan Guo

Lars Thomsen

Christopher R McNeill

Chong-an Di

Yuanping Yi

Xiaozhang Zhu

Daoben Zhu
title: Critical Role of Molecular Symmetry for Charge Transport Properties: A Paradigm Learned from Quinoidal Bithieno[3,4 b]thiophenes
year: 2017

abstract: The design and synthesis of new dye/pigment based semiconductors have made a significant contribution to the development of organic electronics. However, there are few detailed studies on the comparison of isomeric dye/pigment molecules, which play an important role in revealing the molecular structure property device performance relationships. In this study, we, for the first time, compared the thermal stability, optical, electrochemical, molecular assembling and charge transport properties of isomeric angular and linear shaped carbazoledioxazine derivatives, namely Ang CZ and Lin CZ, respectively. While the molecular shapes hardly affect the optical bandgaps and energy levels, they dramatically alter the charge transport characteristics. Accordingly, Lin CZ exhibited a two orders of magnitude higher mobility than Ang CZ, evaluated by thin film transistors (TFTs) Further studies suggested that Lin CZ tends to adopt a denser molecular packing motif and a higher molecular orbital overlapping than Ang CZ which is revealed by grazing incidence wide angle X ray scattering (GIWAXS) atomic force microscopy (AFM) and density functional theory calculations (DFT) More importantly, Lin CZ T, a p extended derivative of Lin CZ, showed a relatively high and stable TFT mobility of over 0.1 cm2 V 1 s 1, which was revealed by using an environmentally benign solvent and a pre aggregation method. Our findings will provide direction for developing more promising molecular semiconductors and organic TFT technology.
author_names: Yang Wang

Hiroki Tatsumi

Rikuo Otsuka

Takehiko Mori

Tsuyoshi Michinobu
title: Highly stable, green solvent processable organic thin film transistors: angular vs. linear shaped carbazoledioxazine derivatives
year: 2018

abstract: Thin film transistors based on regioregular poly(3 hexylthiophene) (PHT) and poly(3 decylthiophene) (PDT) and their binary blends were investigated and the blend composition dependence of the charge carrier mobility was determined. The field effect mobility of holes (mh) in a series of 10 binary blends of poly(3 hexylthiophene) (mh 0.02 cm2/(V s) and poly(3 decylthiophene) (mh 8 x 10 5 cm2/(V s) was found to be relatively high (2 x 10 3 cm2/(V s) and constant over a broad composition range (5 80 wt PDT) Above 80% PDT, the hole mobility decreased exponentially with composition. Atomic force microscopy of the homopolymers and blends confirmed the absence of phase separation in the blends. A similar interlayer d spacing that is intermediate between those of the homopolymers is implied by the constant hole mobility in the single phase crystalline blends of 5 80 wt PDT. These results demonstrate that blends of conjugated polymers are alloy semiconductors in which high and tunable charge carrier mob.
author_names: Amit Babel and

Samson A Jenekhe
title: Field Effect Mobility of Charge Carriers in Blends of Regioregular Poly(3 alkylthiophene)s
year: 2003

abstract: We report structural and electrical transport properties of a family of p stacking soluble organic semiconductors, N,N' dialkyl 3,4,9,10 perylene tetracarboxylic diimides (alkyl pentyl [1] octyl [2] and dodecyl [3] The structures of evaporated polycrystalline films of 1 3 were studied using X ray diffraction and atomic force microscopy. Films of 1 3 pack similarly with the direction of p p overlap in the substrate plane. Organic thin film transistors (OTFTs) based on 1 3 deposited on SiO2 gate dielectric showed linear regime electron mobilities of 0.1, 0.6, and 0.2 cm2/(V s) respectively, corrected for contact resistance. OTFTs of 2 had saturation electron mobilities as high as 1.7 cm2/(V s) with on to off current ratios of 107. Variable temperature measurements were used to examine the charge transport kinetics in the range 80 300 K and revealed (1) thermally activated electron mobilities with activation energies dependent on gate voltage and (2) the presence of well defined isokinetic points, i.e.
author_names: Reid John Chesterfield

John C Mckeen

Christopher R Newman

Paul C Ewbank

Demetrio Antonio da Silva Filho

Jean-Luc Bredas

Larry L Miller

and Kent R Mann

C Daniel Frisbie
title: Organic Thin Film Transistors Based on N Alkyl Perylene Diimides: Charge Transport Kinetics as a Function of Gate Voltage and Temperature
year: 2004