scholarly journals Molecular Gas Adsorption Induced Carrier Transport Studies of Epitaxial Graphene Using IR Reflection Spectroscopy

2012 ◽  
Vol 717-720 ◽  
pp. 665-668 ◽  
Author(s):  
Biplob K. Daas ◽  
W. K. Nomani ◽  
Kevin M. Daniels ◽  
Tangali S. Sudarshan ◽  
Goutam Koley ◽  
...  
Keyword(s):  
Carrier Concentration ◽  
Carrier Transport ◽  
Gas Adsorption ◽  
Epitaxial Graphene ◽  
Surface Conductance ◽  
Transport Studies ◽  
Ir Reflection ◽  
Interband Scattering ◽  
Conductance Changes ◽  
Match Theory

We investigate molecular adsorption doping by electron withdrawing NO2 and electron donating NH3 on epitaxial graphene. Amperometric measurements show conductance changes upon introduction of molecular adsorbents on epitaxial graphene. Conductance changes are a trade-off between carrier concentration and scattering, and manifest at direct current and optical frequencies. We therefore investigate changes in the infrared (IR) reflection spectra to correlate these two frequency domains, as reflectance changes are due to a change of EG surface conductance. We match theory with experimental IR data and extract changes in carrier concentration and scattering due to gas adsorption. Finally, we separate the intraband and interband scattering contributions to the electronic transport under gas adsorption. The results indicate that, under gas adsorption, the influence of interband scattering cannot be neglected, even at DC.

Electrical Characterization of the Graphene-SiC Heterojunction

2012 ◽  
Vol 717-720 ◽  
pp. 641-644
Author(s):  
Travis J. Anderson ◽  
Karl D. Hobart ◽  
Luke O. Nyakiti ◽  
Virginia D. Wheeler ◽  
Rachael L. Myers-Ward ◽  
...  
Keyword(s):  
Electrical Properties ◽  
Charge Carrier ◽  
Graphene Sheet ◽  
Carrier Transport ◽  
Electrical Characterization ◽  
Epitaxial Graphene ◽  
Charge Carrier Transport ◽  
Semiconductor System ◽  
Significant Research

Graphene, a 2D material, has motivated significant research in the study of its in-plane charge carrier transport in order to understand and exploit its unique physical and electrical properties. The vertical graphene-semiconductor system, however, also presents opportunities for unique devices, yet there have been few attempts to understand the properties of carrier transport through the graphene sheet into an underlying substrate. In this work, we investigate the epitaxial graphene/4H-SiC system, studying both p and n-type SiC substrates with varying doping levels in order to better understand this vertical heterojunction.

Synergistic optimization of carrier transport and thermal conductivity in Sn-doped Cu2Te

2018 ◽  
Vol 6 (39) ◽  
pp. 18928-18937 ◽  
Author(s):  
Yuchong Qiu ◽  
Ying Liu ◽  
Jinwen Ye ◽  
Jun Li ◽  
Lixian Lian
Keyword(s):  
Thermal Conductivity ◽  
Fermi Level ◽  
Carrier Concentration ◽  
Power Factor ◽  
Carrier Transport ◽  
Lone Pair ◽  
Thermoelectric Performance ◽  
Degenerate Semiconductors ◽  
Lone Pair Electrons

Doping Sn into the Cu2Te lattice can synergistically enhance the power factor and decrease thermal conductivity, leading to remarkably optimized zTs. The lone pair electrons from the 5s orbital of Sn can increase the DOS near the Fermi level of Cu2Te to promote PF and reduce κe by decreasing the carrier concentration. This study explores a scalable strategy to optimize the thermoelectric performance for intrinsically highly degenerate semiconductors.

Field Effect Mobility of F16PcCu Films in Various Gas Atmospheres

1999 ◽  
Vol 03 (07) ◽  
pp. 667-671 ◽  
Author(s):  
HIROKAZU TADA ◽  
HIROSHI TOUDA ◽  
MASAKI TAKADA ◽  
KAZUMI MATSUSHIGE
Keyword(s):  
Carrier Density ◽  
Field Effect ◽  
Carrier Mobility ◽  
Carrier Transport ◽  
Room Temperature ◽  
Gas Adsorption ◽  
Quick Recovery ◽  
Thermally Activated ◽  
High Carrier ◽  
Gas Molecules

The electron mobility of hexadecafluorophthalocyaninato-copper ( F 16 PcCu ) films was evaluated based on field effect measurements in vacuum and in various gas atmospheres. An Arrhenius plot of the mobility showed that the carrier transport followed a thermally activated hopping mechanism with an activation energy of 0.28 eV. The mobility evaluated for freshly prepared films in ultrahigh vacuum was 2.0 × 10−3 cm 2 V −1 s −1 at room temperature. The electrical conductivity and carrier density were 4.4 × 10−5 S cm −1 and 1.4 × 1017 cm −3 respectively. The high carrier density indicated the existence of impurities acting as electron donors in the films. The field effect carrier mobility increased to 5.7 × 10−3 cm 2 V −1 s −1 in NH 3 atmosphere (100%, 1 atm) and decreased by 75% in the presence of O 2 gas (100%, 1 atm). A quick recovery of mobility was observed when the gas molecules were evacuated, indicating a low capability of gas adsorption.

Thickness Uniformity and Electron Doping in Epitaxial Graphene on SiC

2013 ◽  
Vol 740-742 ◽  
pp. 153-156 ◽  
Author(s):  
Jens Eriksson ◽  
Donatella Puglisi ◽  
Remigijus Vasiliauskas ◽  
Anita Lloyd Spetz ◽  
Rositza Yakimova
Keyword(s):  
Surface Morphology ◽  
Carrier Concentration ◽  
Substrate Surface ◽  
Epitaxial Graphene ◽  
Kelvin Probe ◽  
Surface Restructuring ◽  
Kelvin Probe Microscopy ◽  
Force Microscopy ◽  
Potential Mapping ◽  
Sublimation Growth

Large variations have been observed in the uniformity and carrier concentration of epitaxial graphene grown on SiC by sublimation for samples grown under identical conditions and on nominally on-axis hexagonal SiC (0001) substrates. We have previously shown that these issues are both related to the morphology of the graphene-SiC surface after sublimation growth. Here we present a study on how the substrate polytype, substrate surface morphology and surface restructuring during sublimation growth affect the uniformity and carrier concentration in epitaxial graphene on SiC. These issues were investigated employing surface morphology mapping by atomic force microscopy coupled with local surface potential mapping using Scanning Kelvin probe microscopy.

scholarly journals Growth Condition-Oriented Defect Engineering for Changes in Au–ZnO Contact Behavior from Schottky to Ohmic and Vice Versa

Nanomaterials ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 980 ◽  
Author(s):  
Abu Rana ◽  
Hyun-Seok Kim
Keyword(s):  
Schottky Barrier ◽  
Carrier Concentration ◽  
Carrier Transport ◽  
Defect Density ◽  
High Surface ◽  
Zno Nanorods ◽  
Schottky Contact ◽  
Oxygen Plasma Treatment ◽  
Defect Engineering ◽  
Contact Behavior

ZnO has the built-in characteristics of both ionic and covalent compound semiconductors, which makes the metal–ZnO carrier transport mechanism quite intricate. The growth mechanism-centric change in ZnO defect density and carrier concentration also makes the contact formation and behavior unpredictable. This study investigates the uncertainty in Au–ZnO contact behavior for application-oriented research and the development on ZnO nanostructures. Herein, we explain the phenomenon for how Au–ZnO contact could be rectifying or non-rectifying. Growth method-dependent defect engineering was exploited to explain the change in Schottky barrier heights at the Au–ZnO interface, and the change in device characteristics from Schottky to Ohmic and vice versa. The ZnO nanorods were fabricated via aqueous chemical growth (ACG) and microwave-assisted growth (MAG) methods. For further investigations, one ACG sample was doped with Ga, and another was subjected to oxygen plasma treatment (OPT). The ACG and Ga-doped ACG samples showed a quasi-Ohmic and Ohmic behavior, respectively, because of a high surface and subsurface level donor defect-centric Schottky barrier pinning at the Au–ZnO interface. However, the ACG-OPT and MAG samples showed a more pronounced Schottky contact because of the presence of low defect-centric carrier concentration via MAG, and the removal of the surface accumulation layer via the OPT process.

scholarly journals Measurement of Ultrafast Carrier Dynamics in Epitaxial Graphene

2008 ◽  
Vol 1081 ◽  
Author(s):  
Jahan M. Dawlaty ◽  
Shriram Shivaraman ◽  
Mvs Chandrashekhar ◽  
Michael G. Spencer ◽  
Farhan Rana
Keyword(s):  
Relaxation Times ◽  
Epitaxial Graphene ◽  
Optical Pump ◽  
Carrier Relaxation ◽  
Pump Probe ◽  
Graphene Layers ◽  
Ultrafast Optical ◽  
Interband Scattering ◽  
Ultrafast Carrier ◽  
Probe Spectroscopy

ABSTRACTUsing ultrafast optical pump-probe spectroscopy, we have measured carrier relaxation times in epitaxial graphene layers grown on SiC wafers. We find two distinct time scales associated with the relaxation of nonequilibrium photogenerated carriers. An initial fast relaxation transient in the 70-120 fs range is followed by a slower relaxation process in the 0.4-1.7 ps range. The slower relaxation time is found to be inversely proportional to the degree of crystalline disorder in the graphene layers as measured by Raman spectroscopy. We relate the measured fast and slow time constants to carrier-carrier and carrier-phonon intraband and interband scattering processes in graphene.

scholarly journals Photogenerated Carrier Transport Properties in Silicon Photovoltaics

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Prakash Uprety ◽  
Indra Subedi ◽  
Maxwell M. Junda ◽  
Robert W. Collins ◽  
Nikolas J. Podraza
Keyword(s):  
Solar Cell ◽  
Hall Effect ◽  
Carrier Concentration ◽  
Electrical Transport ◽  
Carrier Transport ◽  
Minority Carrier ◽  
Transport Parameters ◽  
Majority Carrier ◽  
Optical Hall Effect ◽  
P Type

AbstractElectrical transport parameters for active layers in silicon (Si) wafer solar cells are determined from free carrier optical absorption using non-contacting optical Hall effect measurements. Majority carrier transport parameters [carrier concentration (N), mobility (μ), and conductivity effective mass (m*)] are determined for both the n-type emitter and p-type bulk wafer Si of an industrially produced aluminum back surface field (Al-BSF) photovoltaic device. From measurements under 0 and ±1.48 T external magnetic fields and nominally “dark” conditions, the following respective [n, p]-type Si parameters are obtained: N = [(3.6 ± 0.1) × 1018 cm−3, (7.6 ± 0.1) × 1015 cm−3]; μ = [166 ± 6 cm2/Vs, 532 ± 12 cm2/Vs]; and m* = [(0.28 ± 0.03) × me, (0.36 ± 0.02) × me]. All values are within expectations for this device design. Contributions from photogenerated carriers in both regions of the p-n junction are obtained from measurements of the solar cell under “light” 1 sun illumination (AM1.5 solar irradiance spectrum). From analysis of combined dark and light optical Hall effect measurements, photogenerated minority carrier transport parameters [minority carrier concentration (Δp or Δn) and minority carrier mobility (μh or μe)] under 1 sun illumination for both n- and p-type Si components of the solar cell are determined. Photogenerated minority carrier concentrations are [(7.8 ± 0.2) × 1016 cm−3, (2.2 ± 0.2) × 1014 cm−3], and minority carrier mobilities are [331 ± 191 cm2/Vs, 766 ± 331 cm2/Vs], for the [n, p]-type Si, respectively, values that are within expectations from literature. Using the dark majority carrier concentration and the effective equilibrium minority carrier concentration under 1 sun illumination, minority carrier effective lifetime and diffusion length are calculated in the n-type emitter and p-type wafer Si with the results also being consistent with literature. Solar cell device performance parameters including photovoltaic device efficiency, open circuit voltage, fill factor, and short circuit current density are also calculated from these transport parameters obtained via optical Hall effect using the diode equation and PC1D solar cell simulations. The calculated device performance parameters are found to be consistent with direct current-voltage measurement demonstrating the validity of this technique for electrical transport property measurements of the semiconducting layers in complete Si solar cells. To the best of our knowledge, this is the first method that enables determination of both minority and majority carrier transport parameters in both active layers of the p-n junction in a complete solar cell.

Charge-Carrier Transport in Large-Area Epitaxial Graphene

2017 ◽  
Vol 529 (11) ◽  
pp. 1700048 ◽  
Author(s):  
Ferdinand Kisslinger ◽  
Matthias Popp ◽  
Johannes Jobst ◽  
Sam Shallcross ◽  
Heiko B. Weber
Keyword(s):  
Charge Carrier ◽  
Carrier Transport ◽  
Epitaxial Graphene ◽  
Charge Carrier Transport ◽  
Large Area

scholarly journals Fabrication of Novel 2D NiO Nanosheet Branched on 1D-ZnO Nanorod Arrays for Gas Sensor Application

2014 ◽  
Vol 2014 ◽  
pp. 1-6 ◽  
Author(s):  
Le Thuy Hoa ◽  
Huynh Ngoc Tien ◽  
Seung Hyun Hur
Keyword(s):  
Carrier Transport ◽  
Gas Adsorption ◽  
Low Cost ◽  
Zno Nanorods ◽  
Hydrothermal Process ◽  
Large Area ◽  
Highly Sensitive ◽  
P Type ◽  
Reducing Gases ◽  
Nio Nanosheets

Fabrication of 3D structures composed of 1D n-type ZnO nanorods (NRs) and 2D p-type NiO nanosheets (NSs) by a low-cost, low-temperature, and large-area scalable hydrothermal process and its use in highly sensitive NO2gas sensors were studied. The p-n heterojunctions formed by NiO-ZnO interfaces as well as large area two-dimensional NiO NSs themselves increased the adsorption of NO2. Moreover, the charge transfer between NiO and ZnO enhanced the responsivity and sensitivity of NO2sensing even at a concentration of 1 ppm. The 30-min NiO NS growth on ZnO NRs in the hybrid sensor showed the highest sensitivity due to the formation of optimum p-n heterojunctions between ZnO NRs and NiO NSs for gas adsorption and carrier transport. Low responsivity toward reducing gases was also observed.

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