SURFACE POLARON SELF-ENERGY AND EFFECTIVE MASS IN A WURTZITE GaN NANOWIRE

2009 ◽  
Vol 23 (16) ◽  
pp. 3403-3416 ◽  
Author(s):  
LI ZHANG
Keyword(s):  
Effective Mass ◽  
Ground State ◽  
Bulk Material ◽  
Coupling Constants ◽  
Perturbation Approach ◽  
Polar Optical Phonon ◽  
Phonon Coupling ◽  
Phonon Modes ◽  
Self Trapping ◽  
Gan Nanowire

The ground-state self-trapping energy and effective mass of surface polarons in a freestanding wurtzite GaN nanowire (NW) are studied using the second-order perturbation approach. Based on the dielectric continuum and Loudon's uniaxial crystal models, the polar optical phonon modes in the one-dimensional (1D) systems are analyzed, and the vibrating spectra of surface optical (SO) modes and electron–SO phonon coupling functions are discussed and analyzed. The calculations of the ground-state polaron self-trapping energy and the correction of effective mass due to the SO phonon modes in the 1D GaN NWs reveal that the polaron self-trapping energy and the correction of effective mass is far larger than those in 1D GaAs NW systems. The reasons for this obvious difference in the two 1D structures can be attributed to the different electron–phonon coupling constants and electron effective masses of bulk material constituting the two types of 1D confined systems. Finally, the polaronic properties of the wurtzite 1D GaN NWs are compared with those of wurtzite GaN -based two-dimensional quantum wells. The physical origins leading to these characteristics and their distinction in the different-dimensionality systems is carefully analyzed.

EFFECTS OF CONFINED LO AND SO PHONON MODES ON POLARON IN FREESTANDING CYLINDRICAL QUANTUM WIRE WITH PARABOLIC CONFINEMENT

2009 ◽  
Vol 23 (29) ◽  
pp. 3515-3523 ◽  
Author(s):  
ANYUN ZOU ◽  
HONGJING XIE
Keyword(s):  
Effective Mass ◽  
Quantum Wire ◽  
Longitudinal Optical ◽  
Perturbation Approach ◽  
Wire Radius ◽  
Phonon Modes ◽  
Phonon Interaction ◽  
Electron Effective Mass ◽  
Self Energy ◽  
Parabolic Confinement

The electron self-energy and correction to the electron effective mass in a freestanding quantum wire with parabolic confining potential was investigated by the perturbation approach. Both the electron-confined longitudinal optical (LO) phonon and surface optical (SO) phonon interactions were considered. Results shows that, for small wire radius, the contributions of electron–LO phonon interaction to the electron self-energy and the correction to the electron effective mass are relatively small in compare with those of the electron–SO phonon interaction.

Bound polaron in a narrow-band polar crystal

1993 ◽  
Vol 71 (11-12) ◽  
pp. 493-500
Author(s):  
Y. Lépine ◽  
O. Schönborn
Keyword(s):  
Effective Mass ◽  
Ground State ◽  
Narrow Band ◽  
Wave Functions ◽  
Phonon Coupling ◽  
Polar Crystal ◽  
Bound Polaron ◽  
Narrow Bandwidth ◽  
Electron Phonon Coupling ◽  
Shallow Impurities

The ground-state energy of a bound polaron in a narrow-band polar crystal (such as a metal oxide) is studied using variational wave functions. We use a Fröhlich-type Hamiltonian on which the effective mass approximation has not been effected and in which a Debye cutoff is made on the phonon wave vectors. The wave functions that are used are general enough to allow the existence of a band state and of a self-trapped state and are reliable in the nonadiabatic limit. We find that three ground states are possible for this system. First, for small electron–phonon coupling, moderate bandwidth, and shallow impurities, the usual effective-mass hydrogenic ground state is found. For a narrow bandwidth and a deep defect, a collapsed state is predicted in which the polaron coincides with the position of the defect. Finally, for moderate electron–phonon coupling, narrow bandwidth, and a very weak defect, a self-trapped polaron in a hydrogenic state is predicted. Our conclusions are presented as asymptotic expansions and as phase diagrams indicating the values of the parameters for which each phase can be found.

SELF-TRAPPING TRANSITION OF ACOUSTIC POLARON IN SLAB

2013 ◽  
Vol 27 (08) ◽  
pp. 1350050
Author(s):  
JUNHUA HOU ◽  
XIAOMING DONG ◽  
XIAOFENG DUAN
Keyword(s):  
Ground State Energy ◽  
Ground State ◽  
State Energy ◽  
Alkali Halides ◽  
2D Systems ◽  
Phonon Coupling ◽  
Length Unit ◽  
First Derivative ◽  
Electron Phonon Coupling ◽  
Self Trapping

Self-trapping transition of the acoustic polaron in slab is researched by calculating the polaron ground state energy and the first derivative of the ground state energy with respect to the electron–phonon coupling. It is indicated that the possibility of self-trapping transition for acoustic polaron in slab fall in between 3D and 2D systems. The electron may be self-trapped in slab systems of GaN , AlN and alkali halides, if the slab systems are thinner than one over ten of the length unit ℏ/mc.

Fock approximation to the large polaron in a magnetic field

1976 ◽  
Vol 54 (19) ◽  
pp. 1979-1989 ◽  
Author(s):  
Y. Lepine ◽  
D. Matz
Keyword(s):  
Magnetic Field ◽  
Ground State Energy ◽  
Ground State ◽  
State Energy ◽  
Cylindrical Symmetry ◽  
Coupling Constants ◽  
The Novel ◽  
Phonon Coupling ◽  
Electron Phonon Coupling ◽  
Large Polaron

We study the large polaron ground state energy in the presence of a constant and uniform magnetic field within the Fock approximation. By use of a new trial spectrum we find a new upper bound to the ground state energy for all magnetic fields and electron–phonon coupling constants. The trial spectrum has the novel feature of keeping cylindrical symmetry for certain values of coupling, even in the absence of magnetic field.

scholarly journals Resonance and antiresonance in Raman scattering in GaSe and InSe crystals

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
M. Osiekowicz ◽  
D. Staszczuk ◽  
K. Olkowska-Pucko ◽  
Ł. Kipczak ◽  
M. Grzeszczyk ◽  
...  
Keyword(s):  
Raman Scattering ◽  
Temperature Effect ◽  
Band Gap ◽  
Raman Spectra ◽  
Quantum Interference ◽  
Optical Band Gap ◽  
Phonon Coupling ◽  
Phonon Modes ◽  
Electron Phonon Coupling ◽  
Resonant Raman

AbstractThe temperature effect on the Raman scattering efficiency is investigated in $$\varepsilon$$ ε -GaSe and $$\gamma$$ γ -InSe crystals. We found that varying the temperature over a broad range from 5 to 350 K permits to achieve both the resonant conditions and the antiresonance behaviour in Raman scattering of the studied materials. The resonant conditions of Raman scattering are observed at about 270 K under the 1.96 eV excitation for GaSe due to the energy proximity of the optical band gap. In the case of InSe, the resonant Raman spectra are apparent at about 50 and 270 K under correspondingly the 2.41 eV and 2.54 eV excitations as a result of the energy proximity of the so-called B transition. Interestingly, the observed resonances for both materials are followed by an antiresonance behaviour noticeable at higher temperatures than the detected resonances. The significant variations of phonon-modes intensities can be explained in terms of electron-phonon coupling and quantum interference of contributions from different points of the Brillouin zone.

Guided Acoustic Phonon Modes in Layered Anisotropic Nanowires

2003 ◽  
Author(s):  
Osama M. Mukdadi ◽  
Subhendu K. Datta ◽  
Martin L. Dunn
Keyword(s):  
Thermal Conductivity ◽  
Acoustic Phonon ◽  
Energy Transport ◽  
Bulk Material ◽  
Rectangular Cross Section ◽  
Critical Role ◽  
Acoustic Phonons ◽  
Phonon Modes ◽  
Low Velocity ◽  
Analysis Technique

Acoustic phonons play a critical role in energy transport in nanostructures. The dispersion of acoustic phonons strongly influences thermal conductivity. Recent observations show lower values of thermal conductivity in finite dimensional nanostructures than in the bulk material. In this work, we will present results for guided acoustic phonon modes in (a) a bilayered GaAs-Nb nanowire of rectangular cross section and (b) a trapezoidal Si nanowire. The former has been used for phonon counting in a nanocalorimeter for measuring thermal conductivity and the latter is commonly used in MEMS applications. A semi-analytical finite element (SAFE) analysis technique has been used to investigate the effects of layering, anisotropy, and boundaries on the dispersion of modes of propagation. Many interesting features of group velocities are found that show confinements around the corners, in the low velocity layer, and coupling of the longitudinal and flexural modes. These would strongly influence thermal conductivity and might provide means of nondestrutive evaluation of mechanical properties.

Effective mass and ground state of AlAs quantum wells studied by magnetoresistance measurements

1992 ◽  
Vol 71 (1) ◽  
pp. 296-299 ◽  
Author(s):  
Koichi Maezawa ◽  
Takashi Mizutani ◽  
Syoji Yamada
Keyword(s):  
Quantum Wells ◽  
Effective Mass ◽  
Ground State

scholarly journals Acoustic phonon lifetimes limit thermal transport in methylammonium lead iodide

2018 ◽  
Vol 115 (47) ◽  
pp. 11905-11910 ◽  
Author(s):  
Aryeh Gold-Parker ◽  
Peter M. Gehring ◽  
Jonathan M. Skelton ◽  
Ian C. Smith ◽  
Dan Parshall ◽  
...  
Keyword(s):  
Lattice Dynamics ◽  
Acoustic Phonon ◽  
Optoelectronic Devices ◽  
High Energy ◽  
High Energy Resolution ◽  
Phonon Coupling ◽  
Lead Iodide ◽  
Phonon Modes ◽  
Electron Phonon Coupling ◽  
Methylammonium Lead Iodide

Hybrid organic–inorganic perovskites (HOIPs) have become an important class of semiconductors for solar cells and other optoelectronic applications. Electron–phonon coupling plays a critical role in all optoelectronic devices, and although the lattice dynamics and phonon frequencies of HOIPs have been well studied, little attention has been given to phonon lifetimes. We report high-precision momentum-resolved measurements of acoustic phonon lifetimes in the hybrid perovskite methylammonium lead iodide (MAPI), using inelastic neutron spectroscopy to provide high-energy resolution and fully deuterated single crystals to reduce incoherent scattering from hydrogen. Our measurements reveal extremely short lifetimes on the order of picoseconds, corresponding to nanometer mean free paths and demonstrating that acoustic phonons are unable to dissipate heat efficiently. Lattice-dynamics calculations using ab initio third-order perturbation theory indicate that the short lifetimes stem from strong three-phonon interactions and a high density of low-energy optical phonon modes related to the degrees of freedom of the organic cation. Such short lifetimes have significant implications for electron–phonon coupling in MAPI and other HOIPs, with direct impacts on optoelectronic devices both in the cooling of hot carriers and in the transport and recombination of band edge carriers. These findings illustrate a fundamental difference between HOIPs and conventional photovoltaic semiconductors and demonstrate the importance of understanding lattice dynamics in the effort to develop metal halide perovskite optoelectronic devices.

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