Probing the Fermi Energy Level and the Density of States Distribution in PbTe Nanocrystal (Quantum Dot) Solids by Temperature-Dependent Thermopower Measurements

ACS Nano ◽  
2011 ◽  
Vol 5 (6) ◽  
pp. 4810-4817 ◽  
Author(s):  
Dong-Kyun Ko ◽  
Christopher B. Murray
Keyword(s):  
Energy Level ◽  
Quantum Dot ◽  
Density Of States ◽  
Fermi Energy ◽  
Fermi Energy Level ◽  
Temperature Dependent

scholarly journals First-Principles Study of Vacancy and Impurities Defects in Graphene

2021 ◽  
Vol 2 (01) ◽  
pp. 93-102
Author(s):  
Hari Krishna Neupane ◽  
Narayan Prasad Adhikari
Keyword(s):  
Magnetic Properties ◽  
Energy Level ◽  
Density Of States ◽  
Fermi Energy ◽  
First Principles ◽  
Density Functional ◽  
Partial Density ◽  
Fermi Energy Level ◽  
Vacancy Defects ◽  
Impurity Defects

In this work, we have studied the electronic and magnetic properties of 1C atom vacancy defects in graphene (1Cv-d-G), 1N atom impurity defects in graphene (1NI-d-G) and 1O atom impurity defects in graphene (1OI-d-G) materials through first principles calculations based on spin-polarized density functional theory (DFT) method, using computational tool Quantum ESPRESSO (QE) code. From band structure and density of states (DOS) calculations, we found that supercell structure of monolayer graphene is a zero bandgap material. But, electronic bands of 1Cv-d-G, 1NI-d-G and 1OI-d-G materials split around the Fermi energy level and DOS of up & down spins states appear in the Fermi energy level. Thus, 1Cv-d-G, 1NI-d-G and 1OI-d-G materials have metallic properties. We have studied the magnetic properties of pure and defected materials by analyzing density of states (DOS) and partial density of states (PDOS) calculations. We found that graphene and 1OI-d-G materials have non-magnetic properties. On the other hand, 1C vacancy atom and 1N impurity atom induced magnetization in 1Cv-d-G & 1NI-d-G materials by the rebonding of dangling bonds and acquiring significant magnetic moments of values -0.75μB/cell & 0.05μB/cell respectively through remaining unsaturated dangling bond. Therefore, non-magnetic graphene changes to magnetic 1Cv-d-G and 1NI-d-G materials due to 1C atom vacancy defects and 1N atom impurity defects. The 2p orbital of carbon atoms has main contribution of magnetic moment in these defected structures.

Intersubband Transitions in In0.07Ga0.93As/Al0.4Ga0.6As Multiple Quantum Wells

1994 ◽  
Vol 299 ◽  
Author(s):  
F. Szmulowicz ◽  
M. O. Manasreh ◽  
C. Kutsche ◽  
C. E. Stutz
Keyword(s):  
Energy Level ◽  
Quantum Well ◽  
Quantum Wells ◽  
Excited States ◽  
Fermi Energy ◽  
Multiple Quantum Well ◽  
Energy Separation ◽  
Multiple Quantum ◽  
Fermi Energy Level ◽  
Intersubband Transitions

AbstractIntersubband transitions in a series of well-doped ([Si] = 2.0×1018cm−3) In0.07Ga0.93As/Al0.4Ga0.6As multiple quantum well samples were studied as a function of the well width by using the optical absorption technique. A single intersubband transition is observed in samples in which the Fermi energy level is between the ground and the first excited states in the quantum well. On the other hand, two intersubband transitions were recorded in samples where the Fermi energy level lies between the first and the second excited states. These two intersubband transitions were attributed to ground-to-first excited states and first-to-second excited states transitions. The energy separation between the latter two intersubband transitions was found to increase as the well width is increased. The fact that two intersubband transitions were observed in certain samples may suggest that specially designed quantum wells can be used for two color long wavelength infrared detectors.

Graphene-based dual-band independently tunable infrared absorber

Nanoscale ◽  
2018 ◽  
Vol 10 (33) ◽  
pp. 15564-15570 ◽  
Author(s):  
Peng Sun ◽  
Chenglong You ◽  
Amirreza Mahigir ◽  
Tongtong Liu ◽  
Feng Xia ◽  
...  
Keyword(s):  
Energy Level ◽  
Resonant Frequency ◽  
Fermi Energy ◽  
Dual Band ◽  
Fermi Energy Level ◽  
P Absorption

Absorption peaks can independently tune each resonant frequency by only changing the Fermi energy level of one.

scholarly journals Investigation of dopant centres dominating the conduction process in the bulk of un-doped GaSb

2019 ◽  
Vol 13 (4) ◽  
pp. 315-327
Author(s):  
Megersa Wodajo Shura
Keyword(s):  
Energy Level ◽  
Hall Effect ◽  
Fermi Energy ◽  
Activation Energies ◽  
Acceptor Level ◽  
Level System ◽  
Fermi Energy Level ◽  
Majority Carrier ◽  
Temperature Regimes ◽  
Hall Effect Measurements

Abstract In this paper, first, the theoretical description of the effects of the dopant densities and the activation energies on the ionization densities, the chemical potentials corresponding to each dopant levels, the majority carrier densities and the Fermi-energy levels in one-acceptor-level system, highly compensated system and two-acceptor-level system are described in detail. Upon fitting the theoretical to the experimental results obtained by the temperature-dependent Hall effect measurements for three samples of un-doped GaSb, the dopant densities and the activation energies for a system with different dopants are investigated. The obtained results revealed that the dopant activation energy has less (no) effect on the Fermi-energy level and the majority carrier density in the highest temperature regimes. The doping density has also less (no) effect on the Fermi-energy level in the lowest temperature regimes. Finally, fitting of the theoretical to the experimental Hall effect measurements results confirmed the presence of three acceptor and one donor levels dominating the majority carrier densities at different temperature regions in all the samples of un-doped GaSb semiconductor.

scholarly journals Numerical Investigation of Graphene and STO Based Tunable Terahertz Absorber with Switchable Bifunctionality of Broadband and Narrowband Absorption

Nanomaterials ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 2044
Author(s):  
Yan Liu ◽  
Rui Huang ◽  
Zhengbiao Ouyang
Keyword(s):  
Energy Level ◽  
Fermi Energy ◽  
High Performance ◽  
Thermal Control ◽  
Rate Of Change ◽  
Center Frequency ◽  
Fermi Energy Level ◽  
Broadband Absorption ◽  
Terahertz Absorber ◽  
The Cross

A graphene metamaterial and strontium titanate (STO)-based terahertz absorber with tunable and switchable bifunctionality has been numerically investigated in this work. Through electrically tuning the Fermi energy level of the cross-shaped graphene, the bandwidth of the proposed absorber varies continuously from 0.12 THz to 0.38 THz with the absorptance exceeding 90%, which indicates the functionality of broadband absorption. When the Fermi energy level of the cross-shaped graphene is 0 eV, the proposed absorber exhibits the other functionality of narrowband absorption owing to the thermal control of the relative permittivity of STO, and the rate of change of the center frequency is 50% ranging from 0.56 THz to 0.84 THz. The peak intensity of the narrowband absorption approximates to nearly 100% through adjusting the Fermi energy level of the graphene strips. The calculated results indicate that it is not sensitive to the polarization for wide incidence angles. The proposed absorber can realize tunable bifunctionality of broadband absorption with a tunable bandwidth and narrowband absorption with a tunable center frequency, which provides an alternative design opinion of the tunable terahertz devices with high performance for high-density integrated systems.

scholarly journals A Broadband Tunable Terahertz Metamaterial Absorber Based on Single-Layer Complementary Gammadion-Shaped Graphene

Materials ◽  
2020 ◽  
Vol 13 (4) ◽  
pp. 860 ◽  
Author(s):  
Fu Chen ◽  
Yongzhi Cheng ◽  
Hui Luo
Keyword(s):  
Energy Level ◽  
Graphene Sheet ◽  
Fermi Energy ◽  
Single Layer ◽  
Dielectric Substrate ◽  
Transverse Magnetic ◽  
Metamaterial Absorber ◽  
Absorption Capacity ◽  
Fermi Energy Level ◽  
Broadband Absorption

We present a simple design of a broadband tunable metamaterial absorber (MMA) in the terahertz (THz) region, which consists of a single layer complementary gammadion-shaped (CGS) graphene sheet and a polydimethylsiloxane (PDMS) dielectric substrate placed on a continuous metal film. The Fermi energy level (Ef) of the graphene can be modulated dynamically by the applied DC bias voltage, which enables us to electrically control the absorption performance of the proposed MMA flexibly. When Ef = 0.8 eV, the relative bandwidth of the proposed MMA, which represents the frequency region of absorption beyond 90%, can reaches its maximal value of 72.1%. Simulated electric field distributions reveal that the broadband absorption mainly originates from the excitation of surface plasmon polaritons (SPPs) on the CGS graphene sheet. Furthermore, the proposed MMA is polarization-insensitive and has wide angles for both transverse-electric (TE) and transverse-magnetic (TM) waves in the broadband frequency range. The broadband absorption capacity of the designed MMA can be effectively adjusted by varying the Fermi energy level of graphene. Lastly, the absorbance of the MMA can be adjusted from 42% to 99.1% by changing the Ef from 0 eV to 0.8 eV, which is in agreement with the theoretical calculation by using the interference 41theory. Due to its simple structure and flexible tunability, the proposed MMA has potential application prospects in tunable filtering, modulators, sensing, and other multispectral devices.

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