scholarly journals A Theoretical Treatment of THz Resonances in Semiconductor GaAs p–n Junctions

Materials ◽  
2019 ◽  
Vol 12 (15) ◽  
pp. 2412 ◽  
Author(s):  
Mohsen Janipour ◽  
I. Burc Misirlioglu ◽  
Kursat Sendur
Keyword(s):  
Dielectric Function ◽  
Electric Fields ◽  
Semiconductor Heterostructures ◽  
Theoretical Treatment ◽  
Low Loss ◽  
Depletion Zone ◽  
Charge Densities ◽  
As Doping ◽  
Effective Masses ◽  
Spatially Varying

Semiconductor heterostructures are suitable for the design and fabrication of terahertz (THz) plasmonic devices, due to their matching carrier densities. The classical dispersion relations in the current literature are derived for metal plasmonic materials, such as gold and silver, for which a homogeneous dielectric function is valid. Penetration of the electric fields into semiconductors induces locally varying charge densities and a spatially varying dielectric function is expected. While such an occurrence renders tunable THz plasmonics a possibility, it is crucial to understand the conditions under which propagating resonant conditions for the carriers occur, upon incidence of an electromagnetic radiation. In this manuscript, we derive a dispersion relation for a p–n heterojunction and apply the methodology to a GaAs p–n junction, a material of interest for optoelectronic devices. Considering symmetrically doped p- and n-type regions with equal width, the effect of certain parameters (such as doping and voltage bias) on the dispersion curve of the p–n heterojunction were investigated. Keeping in sight the different effective masses and mobilities of the carriers, we were able to obtain the conditions that yield identical dielectric functions for the p- and n-regions. Our results indicated that the p–n GaAs system can sustain propagating resonances and can be used as a layered plasmonic waveguide. The conditions under which this is feasible fall in the frequency region between the transverse optical phonon resonance of GaAs and the traditional cut-off frequency of the diode waveguide. In addition, our results indicated when the excitation was slightly above the phonon resonance frequency, the plasmon propagation attained low-loss characteristics. We also showed that the existence or nonexistence of the depletion zone between the p- and n- interfaces allowed certain plasmon modes to propagate, while others decayed rapidly, pointing out the possibility for a design of selective filters.

New Theoretical Treatment of Electroreflectance from Surfaces and Interfaces Having Large Built-in Fields

1992 ◽  
Vol 261 ◽  
Author(s):  
J. W. Garland ◽  
Z. Zhang ◽  
C. Kim ◽  
D. Yang ◽  
P. M. Raccah
Keyword(s):  
Numerical Calculation ◽  
Dielectric Function ◽  
Electric Fields ◽  
Accurate Determination ◽  
Bound State ◽  
Depletion Region ◽  
Quantum Mechanical ◽  
Theoretical Treatment ◽  
Surfaces And Interfaces

ABSTRACTWe have constructed a completely quantum-mechanical theoretical treatment of the modification of the local dielectric function by intense electric fields. It includes the numerical calculation of depletion-region bound-state energies and wavefunctions as well as band wavefunctions. We use this treatment to construct electroreflectance (ER) lineshapes. Our numerical results differ significantly from those of previously proposed ER lineshapes for GaAs with Nd >> 1016. They yield excellent fits to ER data and allow the accurate determination of doping levels and band bendings from ER data.

scholarly journals Charge Densities above Pulsar Polar Caps

2000 ◽  
Vol 177 ◽  
pp. 463-464
Author(s):  
A. Jessner ◽  
H. Lesch ◽  
Th. Kunzl
Keyword(s):  
Neutron Star ◽  
Electric Field ◽  
Work Function ◽  
Potential Barrier ◽  
Electric Fields ◽  
Surface Potential ◽  
Thermal Emission ◽  
Equilibrium Density ◽  
Charge Densities ◽  
Polar Caps

A simplified model provided the framework for our investigation into the distribution of energy and charge densities above the polar caps of a rotating neutron star. We assumed a neutron star withm= 1.4M⊙,r= 10km, dipolar field |B0| = 1012G,B||Ω and Ω = 2Π · (0.5s)−1. The effects of general relativity were disregarded. The induced accelerating electric fieldE||reachesE0= 2.5 · 1013V m−1at the surface near the magnetic poles. The current density along the field lines has an upper limitnGJ, when the electric field of the charged particle flow cancels the induced electric field: At the polesnGJ(r=rns,θ= 0) = 1.4 · 1017m−3.The work function(surface potential barrier)EWis approximated by the Fermi energyEFof magnetised matter. Following Abrahams and Shapiro (1992) one needs to revise the surface density from the canonical 1.4 · 108kg m−3down toρFe = 2.9 · 107kg m−3. Withwe obtain a value ofEF=Ew= 417eV. There are two relevant particle emission processes:Field (cold cathode) emissionby quantum-mechanical tunneling of charges through the surface potentialandthermal emissionwhich is a purely classical process. In strong electric fields it is enhanced by the lowering of the potential barrier due to the Schottky effect. The combined Dushman-Schottky equationwithtells us, thatat temperatures> 2 · 105K the the Goldreich-Julian current can be supplied thermal emission alone. The surface temperature however has a lower limit in the order of 105K due to the rotational braking. Therefore, in most cases a sufficient supply of charges for the Goldreich-Julian current is available and the electrical field accelerating the particles will be quenched as a result of their abundance. Otherwise a residual equilibrium electric field Eeqremains with:and hence the equilibrium density is:n=nfieid(Eeq,EW) +nDS(Eeq,EW,T) For a temperature just below the onset of thermal emission (T= 1.85 · 105K) the charge density is found to vary almost linearly with the work functionEWfor values ofEWbetween 0.3 and 2 keV. At the chosen value forEWof 417 eVthe residual electric field amounts to only 8.5% of the vacuum value. Even in the residual electric field the particles are rapidly accelerated to relativistic energies balanced by inverse Compton and curvature radiation losses.

scholarly journals Mapping atomic electric fields and charge densities by four-dimensional STEM

2017 ◽  
Vol 73 (a2) ◽  
pp. C119-C119
Author(s):  
Knut Müller-Caspary ◽  
M. Duchamp ◽  
F. F. Krause ◽  
A. Beche ◽  
F. Winkler ◽  
...  
Keyword(s):  
Electric Fields ◽  
Charge Densities

Low-loss Electron Energy-loss Spectroscopy and Dielectric Function of Biological and Geological Polymorphs of CaCO3

1999 ◽  
Vol 5 (5) ◽  
pp. 358-364 ◽  
Author(s):  
Kalpana S. Katti ◽  
Maoxu Qian ◽  
Daniel W. Frech ◽  
Mehmet Sarikaya
Keyword(s):  
Energy Loss ◽  
Electron Energy ◽  
Dielectric Function ◽  
Electronic Structures ◽  
Microstructural Characterization ◽  
Low Loss ◽  
Composite Microstructure ◽  
Abalone Shell ◽  
Electron Energy Loss ◽  
Electron Excitations

Previous work on microstructural characterization has shown variations in terms of defects and organization of nanostructures in the two polymorphs of calcium carbonate, calcite, and aragonite in mollusc shells. Large variations in mechanical properties are observed between these sections which have been attributed to variations in composite microstructure as well as intrinsic properties of the inorganic phases. Here we present local low-loss electron energy-loss spectroscopic (EELS) study of calcitic and aragonitic regions of abalone shell that were compared to geological (single-crystal) counterpart polymorphs to reveal intrinsic differences that could be related to organismal effects in biomineralization. In both sets of samples, local dielectric function is computed using Kramer-Kronig analysis. The electronic structures of biogenic and geological calcitic materials are not significantly different. On the other hand, electronic structure of biogenic aragonite is remarkably different from that of geological aragonite. This difference is attributed to the increased contribution from single electron excitations in biogenic aragonite as compared to that of geological aragonite. Implications of these changes are discussed in the context of macromolecular involvement in the making of the microstructures and properties in biogenic phases.

Novel Polar-fluoropolymer Blends with Tailored Nanostructures for High Energy Density and Low Loss Capacitor Applications

2012 ◽  
Vol 1403 ◽  
Author(s):  
Shan Wu ◽  
Minren Lin ◽  
David S-G. Lu ◽  
Lei Zhu ◽  
Q. M. Zhang
Keyword(s):  
Dielectric Loss ◽  
Energy Density ◽  
Electric Fields ◽  
Vinylidene Fluoride ◽  
High Energy ◽  
High Energy Density ◽  
Low Loss ◽  
Blend Films ◽  
Low Dielectric ◽  
High Electric Fields

ABSTRACTDielectric polymers with high energy density with low loss at high electric fields are highly desired for many energy storage and regulation applications. A polar-fluoropolymer blend consisting of a high energy density polar-fluoropolymer of poly(vinylidene fluoride-chlorotrifluoroethylene) (P(VDF-CTFE)) with a low dielectric loss polymer of poly(ethylene-chlorotrifluoroethylene) (ECTFE) was developed and investigated. We show that the two polymers are partially miscible which leads to blends with high energy density and low loss. Moreover, by introducing crosslinking to further tailor the nano-structures of the blends a markedly reduction of losses in the blend films at high field can be achieved. The crosslinked blend films show a dielectric constant of 7 with a dielectric loss of 1% at low field. Furthermore, the blends maintain a high energy density and low loss (∼3%) at high electric fields (> 250 MV/m).

Elastic Constants of Nematic Liquid Crystals

1972 ◽  
Vol 27 (6) ◽  
pp. 966-976 ◽  
Author(s):  
Hans Gruler ◽  
Terry J. Scheffer ◽  
Gerhard Meier
Keyword(s):  
Magnetic Fields ◽  
Electric Fields ◽  
Detailed Comparison ◽  
Theoretical Treatment ◽  
Electrical Capacitance ◽  
Normal Deformation ◽  
Electric And Magnetic Fields ◽  
The Magnetic Field ◽  
Dynamic Phenomena ◽  
Good Agreement

Abstract We present a theoretical treatment and give experimental observations of the deformation that occurs in a nematic liquid crystal when electric or magnetic fields are applied. We consider only normal deformations in the nematic material where fluid flow and other dynamic phenomena play no role. Three important sample geometries are considered in the magnetic field, and the experimentally observed deformations are in good agreement with theory. The normal deformation induced by electric fields is of interest from a device standpoint, and we give a solution for the deformation that is valid even for large dielectric anisotropics. This solution has been experimentally verified. We give a detailed comparison of the distortions produced by electric and magnetic fields and show that the deformations are of a similar form even though the field is nonuniform in the electric case. The change in birefringence and electrical capacitance as a function of distortion is discussed as a means of observing the deformation.

scholarly journals Contribution of Drude and Brendel Model Terms to the Dielectric Function; A case of TiO2:Nb Thin Films

2018 ◽  
Vol 1 (1) ◽  
pp. 3-7
Author(s):  
Christopher Mkirema Maghanga ◽  
Maurice M Mwamburi
Keyword(s):  
Thin Films ◽  
Dielectric Function ◽  
Parametric Modeling ◽  
Free Electrons ◽  
As Doping ◽  
Niobium Doped ◽  
Spectrophotometric Data ◽  
Drude Term ◽  
Individual Contributions ◽  
The Individual

Parametric modeling provides a mean of deeper understanding to the properties of materials. Dielectric function is one of the key parameters which can provide information on the dielectric nature of a thin film or bulk materials. It can be obtained by modeling the material using appropriate existing, new or modified models. In our work, we utilized existing Brendel and Drude models to extract the optical constants from spectrophotometric data of fabricated undoped and niobium doped titanium oxide thin films. The individual contributions by the two models were studied to establish influence on the dielectric function. The effect of dopants on their influences was also analyzed. Results indicate a minimal contribution from the Drude term due to the dielectric nature of the undoped films. However as doping levels increase, the rise in the concentration of free electrons favors the use of Drude model.

scholarly journals Effective masses and complex dielectric function of cubic HfO2

2004 ◽  
Vol 85 (21) ◽  
pp. 5022-5024 ◽  
Author(s):  
J. C. Garcia ◽  
L. M. R. Scolfaro ◽  
J. R. Leite ◽  
A. T. Lino ◽  
V. N. Freire ◽  
...  
Keyword(s):  
Dielectric Function ◽  
Complex Dielectric Function ◽  
Effective Masses
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