Simulation of InAsSb/InGaAs Quantum Dots for Optical Device Applications

2004 ◽  
Vol 851 ◽  
Author(s):  
Paul von Allmen ◽  
Seungwon Lee ◽  
Fabiano Oyafuso
Keyword(s):  
Quantum Dots ◽  
Electronic Structure ◽  
Band Gap ◽  
Atmospheric Chemistry ◽  
Energy Gap ◽  
Tight Binding ◽  
Atomic Interaction ◽  
Optical Detectors ◽  
Wide Range ◽  
Device Applications

ABSTRACTSelf-assembled InAsSb/InGaAs quantum dots are candidates for optical detectors and emitters in the 2–5 micron band with a wide range of applications for atmospheric chemistry studies. It is known that while the energy band gap of unstrained bulk InAs1−xSbx is smallest for x=0.62, the biaxial strain for bulk InAs1−xSbx grown on In0.53Ga0.47As shifts the energy gap to higher energies and the smallest band gap is reached for x=0.51. The aim of the present study is to examine how the electronic confinement in the quantum dots modifies these simple considerations. We have calculated the electronic structure of lens shaped InAs1−xSbx quantum dots with diameter 37 nm and height 4 nm embedded in a In0.53Ga0.47As matrix of thickness 7 nm and lattice matched to an InP buffer. The relaxed atomic positions were determined by minimizing the elastic energy obtained from a valence force field description of the inter-atomic interaction. The electronic structure was calculated with an empirical tight binding approach. For Sb concentrations larger than x=0.5, it is found that the InSb/ In0.53Ga0.47As heterostructure becomes type II leading to no electron confined in the dot. It is also found that the energy gap decreases with increasing Sb content in contradiction with previous experimental results. A possible explanation is a significant variation is quantum dot size with Sb content.

scholarly journals The Band-Gap Studies of Short-Period CdO/MgO Superlattices

2021 ◽  
Vol 16 (1) ◽  
Author(s):  
Ewa Przeździecka ◽  
P. Strąk ◽  
A. Wierzbicka ◽  
A. Adhikari ◽  
A. Lysak ◽  
...  
Keyword(s):  
Band Gap ◽  
Layer Thickness ◽  
Energy Gap ◽  
Band Gaps ◽  
Short Period ◽  
Wide Range ◽  
Salt Structure ◽  
Short Period Superlattices ◽  
Direct Band ◽  
Sublayer Thickness

AbstractTrends in the behavior of band gaps in short-period superlattices (SLs) composed of CdO and MgO layers were analyzed experimentally and theoretically for several thicknesses of CdO sublayers. The optical properties of the SLs were investigated by means of transmittance measurements at room temperature in the wavelength range 200–700 nm. The direct band gap of {CdO/MgO} SLs were tuned from 2.6 to 6 eV by varying the thickness of CdO from 1 to 12 monolayers while maintaining the same MgO layer thickness of 4 monolayers. Obtained values of direct and indirect band gaps are higher than those theoretically calculated by an ab initio method, but follow the same trend. X-ray measurements confirmed the presence of a rock salt structure in the SLs. Two oriented structures (111 and 100) grown on c- and r-oriented sapphire substrates were obtained. The measured lattice parameters increase with CdO layer thickness, and the experimental data are in agreement with the calculated results. This new kind of SL structure may be suitable for use in visible, UV and deep UV optoelectronics, especially because the energy gap can be precisely controlled over a wide range by modulating the sublayer thickness in the superlattices.

Electronic Structure and Surface Properties of SrBi2Ta2O9 and Related Oxides

1997 ◽  
Vol 493 ◽  
Author(s):  
J Robertson ◽  
C W Chen
Keyword(s):  
Electronic Structure ◽  
Band Gap ◽  
Conduction Band ◽  
Tight Binding ◽  
Schottky Barriers ◽  
Band Edge ◽  
Conduction Band Edge ◽  
Edge States ◽  
Tight Binding Method ◽  
S States

ABSTRACTThe electronic structure of SrBi2Ta2O9 and related oxides such as SrBi2Nb2O9, Bi2WO6 and Bi3Ti4O12 have been calculated by the tight-binding method. In each case, the band gap is about 4.1 eV and the band edge states occur on the Bi-O layers and consist of mixed O p/Bi s states at the top of the valence band and Bi p states at the bottom of the conduction band. The main difference between the compounds is that Nb 5d and Ti 4d states in the Nb and Ti compounds lie lower than the Ta 6d states in the conduction band. The surface pinning levels are found to pin Schottky barriers 0.8 eV below the conduction band edge.

scholarly journals Temperature dependent Band gap Correction model using tight-binding approach for UTB device simulations

2022 ◽  
Author(s):  
Nalin Vilochan Mishra ◽  
Ravi Solanki ◽  
Harshit Kansal ◽  
Aditya S Medury
Keyword(s):  
Band Structure ◽  
Band Gap ◽  
Tight Binding ◽  
Thin Body ◽  
Temperature Dependent ◽  
Minor Variation ◽  
Correction Model ◽  
Wide Range ◽  
Channel Thickness ◽  
Semi Empirical

<div>Ultra-thin body (UTB) devices are being used in many electronic applications operating over a wide range of temperatures. The electrostatics of these devices depends on the band structure of the channel material, which varies with temperature as well as channel thickness. The semi-empirical tight binding (TB) approach is widely used for calculating channel thickness dependent band structure of any material, at a particular temperature, where TB parameters are defined. For elementary semiconductors like Si, Ge and compound semiconductors like GaAs, these TB parameters are generally defined at only 0 K and 300 K. This limits the ability of the TB approach to simulate the electrostatics of these devices at any other intermediate temperatures.</div><div>In this work, we analyze the variation of band structure for Si, Ge and GaAs over different channel thicknesses at 0 K and 300 K (for which TB parameters are available), and show that the band curvature at the band minima has minor variation with temperature, whereas the change of band gap significantly affects the channel electrostatics. Based on this finding, we propose an approach to simulate the electrostatics of UTB devices, at any temperature between 0 K and 300 K, using TB parameters defined at 0 K, along with a suitable channel thickness and temperature dependent band gap correction. </div>

Influence of Structural Parameters to Engineer the Band Gaps in Ternary Pnictide Semiconductors - Theory as a Tool

2007 ◽  
Vol 124-126 ◽  
pp. 57-60 ◽  
Author(s):  
Rita John
Keyword(s):  
Band Gap ◽  
Energy Gap ◽  
Structural Parameters ◽  
Tight Binding ◽  
Band Gaps ◽  
Theoretical Tool ◽  
Linear Muffin Tin Orbital

The band gap anomaly exhibited by ABC2 : A = Cd; B = Si,Ge,Sn; C = P,As pnictides with respect to their binary analogs GaP, Ga0.5In0.5P, InP, GaAs, Ga0.5In0.5As, InAs is studied using Tight Binding Linear Muffin Tin Orbital (TBLMTO) method as an investigating theoretical tool. The influence of the structural parameters, η and u are analyzed to enable one to tune energy gap to make tailor made compounds.

scholarly journals Influence of Size Effect on the Electronic and Elastic Properties of Graphane Nanoflakes: Quantum Chemical and Empirical Investigations

2015 ◽  
Vol 2015 ◽  
pp. 1-5 ◽  
Author(s):  
A. S. Kolesnikova ◽  
M. M. Slepchenkov ◽  
M. F. Lin ◽  
O. E. Glukhova
Keyword(s):  
Electronic Structure ◽  
Comparative Analysis ◽  
Size Effect ◽  
Ionization Potential ◽  
Quantum Chemical ◽  
Energy Gap ◽  
Tight Binding ◽  
Empirical Method ◽  
Tight Binding Method ◽  
Graphene Nanoflake

By application of empirical method it is found that graphene nanoflake (graphane) saturated by hydrogen is not elastic material. In this case, the modulus of the elastic compression of graphane depends on its size, allowing us to identify the linear parameters of graphane with maximum Young’s modulus for this material. The electronic structure of graphane nanoflakes was calculated by means of the semiempirical tight-binding method. It is found that graphane nanoflakes can be characterized as dielectric. The energy gap of these particles decreases with increasing of the length tending to a certain value. At the same time, the ionization potential of graphane also decreases. A comparative analysis of the calculated values with the same parameters of single-walled nanotubes is performed.

Energetics at the Edge: Direct Optical Mapping of Bulk and Interfacial Electronic Structure in CdSe Quantum Dots using Broadband Electronic Sum Frequency Generation Microspectroscopy

2019 ◽  
Author(s):  
Brianna R. Watson ◽  
Benjamin Doughty ◽  
Tessa Calhoun
Keyword(s):  
Quantum Dots ◽  
Electronic Structure ◽  
Sum Frequency Generation ◽  
Cdse Quantum Dots ◽  
Trap States ◽  
Sum Frequency ◽  
Interfacial Electronic Structure ◽  
Wide Range ◽  
Frequency Generation ◽  
Gap States

Understanding and controlling the electronic structure of nanomaterials is the key to tailoring their use in a wide range of practical applications. Despite this need, many important electronic states are invisible to conventional optical measurements and are typically identified indirectly based on their inferred impact on luminescence properties. This is especially common and important in the study of nanomaterial surfaces and their associated defects. Surface trap states play a crucial role in photophysical processes yet remain remarkably poorly understood. Here we demonstrate for the first time that broadband electronic sum frequency generation (eSFG) microspectroscopy can directly map the optically bright and dark states of nanoparticles, including the elusive below gap states. This new approach is applied to model cadmium selenide (CdSe) quantum dots (QDs), where the energies of interfacial trap states have eluded direct optical characterization for decades. Our eSFG measurements show clear signatures of electronic transitions both above the band gap, which we assign to previously reported one- and two-photon transitions associated with the CdSe core, as well as broad spectral signatures below the bandgap that are attributed to interfacial trap states. In addition to the core states, this analysis reveals two distinct distributions of below gap states providing the first direct optical measurement of both shallow and deep trapping sites on this system. Finally, chemical modification of the surfaces via oxidation results in the relative increase in the signals originating from the interfacial trap states. Overall, our eSFG experiments provide an avenue to directly map the entirety of QD bulk and interfacial electronic structure, which is expected to open up opportunities to study how these materials are grown <i>in situ</i> and how surface states can be controlled to tune functionality.

Theoretical investigation of energy gap bowing in CdSxSe1−x alloy quantum dots

2017 ◽  
Vol 19 (22) ◽  
pp. 14495-14502
Author(s):  
Laxman Tatikondewar ◽  
Anjali Kshirsagar
Keyword(s):  
Density Functional Theory ◽  
Quantum Dots ◽  
Electronic Structure ◽  
Theoretical Investigation ◽  
Density Functional ◽  
Energy Gap ◽  
Electronic Structure Calculations ◽  
Functional Theory ◽  
Alloy Quantum Dots ◽  
Structure Calculations

To investigate energy gap bowing in homogeneously alloyed CdSxSe1−x quantum dots (QDs) and to understand whether it is different from bulk, we perform density functional theory based electronic structure calculations for spherical QDs of different compositions x (0 ≤ x ≤ 1) and of varying sizes (2.2 to 4.6 nm).

The External Crystal Structure and Electronic Structure are Simulated about Ge0.6Si0.4 Quantum Dots

2016 ◽  
Vol 852 ◽  
pp. 329-335
Author(s):  
Zhi Ke Gao ◽  
Chong Wang ◽  
Yu Yang ◽  
Jie Yang ◽  
Li Qiao Chen
Keyword(s):  
Quantum Dots ◽  
Electronic Structure ◽  
Band Gap ◽  
Silicon Germanium ◽  
Density Functional ◽  
Simulation Method ◽  
Dynamics Simulation ◽  
Band Shift ◽  
Functional Theory ◽  
Germanium Alloy

The alloy Ge0.6Si0.4 quantum dots were studied by using density functional theory. The change of the electronic structure of each crystal which grown in different simulation temperature condition were investigated by molecular dynamics simulation method. The results indicate that quantum dots of silicon germanium alloy occupy the narrow band gap of each crystal face from low to high temperature conditions. Since the atomic density and crystal configuration is different, the band gap values are relatively different. The mechanism of dielectric constant transition is well explained based on the inter-band and in-band shift of band structure.

ELECTRONIC STRUCTURE AND QUANTUM PHASE TRANSITION IN MULTI-WALL CARBON NANOTUBES

2007 ◽  
Vol 21 (25) ◽  
pp. 4377-4386 ◽  
Author(s):  
SHI-DONG LIANG
Keyword(s):  
Phase Transition ◽  
Carbon Nanotubes ◽  
Electronic Structure ◽  
Quantum Phase Transition ◽  
Essential Role ◽  
Energy Gap ◽  
Tight Binding ◽  
Quantum Phase ◽  
Multi Wall Carbon Nanotubes ◽  
Structure Characteristics

The electronic structure of the multi-wall carbon nanotubes (MWCN) is studied theoretically by the tight-binding approach. The interwall coupling between layers plays an essential role in the electronic structure. With an increase of the interwall coupling, the energy gap of the semiconducting MWCNs will decrease and eventually vanish, giving rise to the semiconductor–metal quantum phase transition. The metallic layer in the MWCN dominates the electronic structure characteristics near the Fermi level (gapless).

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