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Radiative life time of an exciton confined in a strained GaN/Ga_(1-x)Al_xN cylindrical dot:built-in electric field effects

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Chinese Physics B 2011年第7期20卷 367-372页

作者： Chang Woo Lee a.john peter Department of Chemical Engineering and Green Energy Center College of EngineeringKyung Hee University1 SeochunGihungYonginGyeonggi 446-701Republic of Korea Department of Physics Government Arts and Science CollegeMelur-625106India

The binding energy of an exciton in a wurtzite GaN/GaAlN strained cylindrical quantum dot is investigated theoretically. The strong built-in electric field due to the spontaneous and piezoelectric polarizations of a GaN/GaAlN quantum dot is included. Numerical calculations are performed using a variational procedure within the single band effective mass approximation. Valence-band anisotropy is included in our theoretical model by using different hole masses in different spatial directions. The exciton oscillator strength and the exciton lifetime for radiative recombination each as a function of dot radius have been computed. The result elucidates that the strong built-in electric field influences the oscillator strength and the recombination life time of the exciton. It is observed that the ground state exciton binding energy and the interband emission energy increase when the cylindrical quantum dot height or radius is decreased, and that the exciton binding energy, the oscillator strength and the radiative lifetime each as a function of structural parameters （height and radius） sensitively depend on the strong built-in electric field. The obtained results are useful for the design of some opto-photoelectronic devices.

关键词： quantum dot donor bound excitons oscillator strength

Electronic and optical properties of CdS/CdZnS nanocrystals

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Chinese Physics B 2012年第8期21卷 441-448页

作者： a.john peter Chang Woo Lee epartment of Chemical Engineering and Green Energy Center College of EngineeringKyung Hee University1 SeochunGihungYonginGyeonggi 446-701S.Korea Department of Physics Govt.Arts CollegeMelurMadurai-62510India Department of Chemical Engineering and Green Energy Center College of EngineeringKyung Hee University1 SeochunGihungYonginGyeonggi 446-701S.Korea

Cd1-xZnxS nanocrystals are prepared by a co-precipitation method with different atomic fractions of Zn. The texture, structural transformation and optical properties with increasing x value in Cd1-xZnxS are studied with scanning electron microscopy, electron diffraction patterning, and absorption spectra respectively. Quantum confinement in a strained CdS/Cd1-xZnxS related nanodot with various Zn content values is investigated theoretically. Binding energies on exciton bound CdS/CdxZn1-xS quantum dot are computed, with consideration of the internal electric field induced by the spontaneous and piezoelectric polarizations, and thereby the interband emission energy is calculated as a function of the dot radius. The optical band gap from the UV absorption spectrum is compared with the interband emission energy computed theoretically. Our results show that the average diameter of composite nanoparticles ranges from 3 nm to 6 nm. The X-ray diffraction pattern shows that all the peaks shift towards the higher diffracting angles with an increase in Zn content. The lattice constant gradually decreases as the Zn content increases. The strong absorption edge shifts towards the lower wavelength region and hence the band gap of the films increases as the Zn content increases. The values of the absorption edge are found to shift towards the shorter wave length region and hence the direct band gap energy varies from 2.5 eV for the CdS film and 3.5 eV for the ZnS film. Our numerical results are in good agreement with the experimental results.

关键词： quantum dots quasicrystals semiconductor

Photo-Induced Electron Spin Polarization in a Narrow Band Gap Semiconductor Nanostructure

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Chinese Physics Letters 2012年第11期29卷 186-190页

作者： a.john peter Chang Woo Lee Department of Chemical Engineering and Green Energy Center College of EngineeringKyung Hee University1 SeochunGihungYonginGyeonggi 446-701S.Korea

Photo-induced spin dependent electron transmission through a narrow gap InSb/InGa_(x)Sb_(1-x) semiconductor symmetric well is theoretically studied using transfer matrix *** transparency of electron transmission is calculated as a function of electron energy for different concentrations of *** spin-polarized photon assisted resonant tunnelling in the heterostructure due to Dresselhaus and Rashba spin-orbit coupling induced splitting of the resonant level and compressed spin-polarization are *** results show that Dresselhaus spin-orbit coupling is dominant for the photon effect and the computed polarization efficiency increases with the photon effect and the gallium concentration.

关键词： polarization resonant photon

Energy Gap Dependence on Mn Content in a Diluted Magnetic Quantum Dot

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Chinese Physics Letters 2011年第4期28卷 201-204页

作者： P.Nalini a.john peter Department of Physics Yadava College Govindarajan CampusThiruppalaiMadurai-625014India Department of Physics Govt.Arts and Science CollegeMelur-625106MaduraiIndia

Positively charged donor exciton binding energy is computed as a function of quantum-dot size within the single band effective mass approximation for different Mn contents in Cd_(1)−x_(𝑥in)Mn_(x𝑥in)Te/Cd_(1−xout)𝑥outMn_(xout)𝑥*** exciton bound polaron is computed for 0≤x𝑥≤0.08,on the Mn mole *** determine the energy gap using the mean field approximation and incorporate the exchange interaction between the carrier and the magnetic *** interband emission energy is studied with the height and radius of the cylindrical quantum ***-band anisotropy is included in our theoretical model using different hole masses in different spatial *** polaronic shifts as functions of quantum-dot radius and Mn concentration are estimated using the mean field *** is found that(i)the energy gap depends on the Mn mole fraction,(ii)it increases linearly with an increase in Mn content,and(iii)the effect is more pronounced for a narrow dot,showing the quantum size *** results are in good agreement with other recently published reports.

关键词： theory quantum radius

Effect of p-d exchange with an itinerant carrier in a GaMnAs quantum dot

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Journal of Semiconductors 2013年第7期34卷 1-6页

作者： D.Lalitha a.john peter Department of Physics GTN College Department of Physics Government Arts College

Hydrogenic acceptor binding energy as a function of dot radius in a GaMnAs/Ga_（0.6）Al_（0.4）As quantum dot is calculated including the exchange interaction of Mn alloy content with an itinerant *** are performed by varying its dot radius,for various Mn alloy contents in GaMnAs quantum dot within a single band effective mass approximation using variational *** spin polaronic energy of the acceptor impurity for different Mn^（2＋） is evaluated for different dot radii using a mean field theory in the presence of magnetic field *** magnetization is computed in the influence of magnetic field and the Mn *** effective g-factor of the valence band electron with the inclusion of effects of Mn ion impurities is found in the influence of the magnetic *** exchange coupling constant is calculated for various magnetic field *** results show that the p-d exchange interaction in the GaMnAs/Ga_（0.6）Al_（0.4）As quantum dot has a strong dependence on spatial confinement,effect of magnetic field strength and the Mn alloy *** results are in good agreement with the other investigators.

关键词： quantum dot acceptor diluted magnetic semiconductors

Magneto-polaron induced intersubband optical transition in a wide band gap Ⅱ–Ⅵ semiconductor quantum dot

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Journal of Semiconductors 2015年第3期36卷 1-6页

作者： P.Christina Lily Jasmine a.john peter Department of Physics N.M.S.Sermathai Vasan College for Women Department of Physics Government Arts College

Effects of LO-phonon contribution on the electronic and the optical properties are investigated in a ***.2 Se/ZnSe quantum dot in the presence of magnetic field strength. The magneto-polaron induced hydro- genic binding energy as a function of dot radius in the wide band gap quantum dot is calculated. The oscilla- tor strength and the spontaneous lifetime are studied taking into account the spatial confinement, magnetic field strength and the phonon contribution. Numerical calculations are carried out using variational formulism within the single band effective mass approximation. The optical properties are computed with the compact density matrix method. The magneto-polaron induced optical gain as a function of photon energy is observed. The results show that the optical telecommunication wavelength in the fiber optic communications can be achieved using CdSe/ZnSe semiconductors and it can be tuned with the proper applications of external perturbations.

关键词： electronic states optical absorption intersubband transition quantum dot

Nonlinear Optical Properties in a Quantum Dot of Some Polar Semiconductors

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Chinese Physics Letters 2013年第10期30卷 147-151页

作者： A.Azhagu Parvathi a.john peter Chang Kyoo Yoo Department of Physics VV Vanniaperumal College for WomenVirudhunagar-626001India Department of Physics Govt.Arts and Science CollegeMelur-625106MaduraiIndia Center for Environmental Studies/Green Energy Center Department of Environmental Science and EngineeringCollege of EngineeringKyung Hee UniversitySeocheon-dong 1Giheung-guYongin-SiGyeonggi-Do 446-701South Korea

Exciton binding energy,interband emission energy,oscillator strength,and some nonlinear optical properties in quantum dots made up of polar semiconductors are computed with the geometrical *** effects of the interaction of charge carriers with the longitudinal optical phonons on the exciton binding energy are *** anisotropy of the effective masses of holes is incorporated throughout the *** optical exciton absorption of Ⅱ–Ⅵ systems based on some polar semiconductors in the presence of LO phonons is *** optical rectification coefficient associated with the intersubband transitions in a quantum dot of polar semiconductors is *** of refractive index with the photon energy in a polar quantum dot are *** results show that the polar bound excitons in Ⅱ–Ⅵ based polar semiconductors depend on the geometrical confinement,and the nonlinear optical properties strongly depend on the polar materials.

关键词： materials Nonlinear semiconductors

Dielectric confinement on exciton binding energy and nonlinear optical properties in a strained Zn_(1-x_(in))Mg_(x(in))Se/Zn_(1-x(out))Mg_(x(out))Se quantum well

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Journal of Semiconductors 2012年第9期33卷 1-7页

作者： J.Abraham Hudson Mark a.john peter Department of Physics NPR Arts&Science CollegeNathamDindigul-624401India Department of Physics Government Arts CollegeMelur-625106MaduraiIndia

The band offsets for a Zn1-xin Mgxin Se/Zn1-xout Mgxout Se quantum well heterostructure are determined using the model solid theory. The heavy hole exciton binding energies are investigated with various Mg alloy contents. The effect of mismatch between the dielectric constants between the well and the barrier is taken into account. The dependence of the excitonic transition energies on the geometrical confinement and the Mg alloy is discussed. Non-linear optical properties are determined using the compact density matrix approach. The linear, third order non-linear optical absorption coefficient values and the refractive index changes of the exciton are calculated for different concentrations of magnesium. The results show that the occurred blue shifts of the resonant peak due to the Mg incorporation give the information about the variation of two energy levels in the quantum well width.

关键词： interband emission energy exciton binding energy quantum well

The nonlinear optical properties of a magneto-exciton in a strained Ga_(0.2)In_(0.8)As/GaAs quantum dot

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Chinese Physics B 2013年第10期22卷 479-485页

作者： N.R.Senthil Kumar a.john peter Chang Kyoo Yoo Department of Physics SBM College of Engineering and Technology Department of Physics Govt.Arts CollegeMelur-625 106MaduraiIndia Center for Environmental Studies/Green Energy Center Deptartment of Environmental Science and EngineeringCollege of EngineeringKyung Hee UniversitySeocheon-dong 1Giheung-guYongin-SiGyeonggi-Do446-701South Korea

The magnetic field-dependent heavy hole excitonic states in a strained ***/GaAs quantum dot are investi- gated by taking into account the anisotropy, non-parabolicity of the conduction band, and the geometrical confinement. The strained quantum dot is considered as a parabolic dot of InAs embedded in a GaAs barrier material. The dependence of the effective excitonic g-factor as a function of dot radius and the magnetic field strength is numerically measured. The interband optical transition energy as a function of geometrical confinement is computed in the presence of a mag- netic field. The magnetic field-dependent oscillator strength of interband transition under the geometrical confinement is studied. The exchange enhancements as a function of dot radius are observed for various magnetic field strengths in a strained ***/GaAs quantum dot. Heavy hole excitonic absorption spectra, the changes in refractive index, and the third-order susceptibility of third-order harmonic generation are investigated in the Gao.2Ino.8As/GaAs quantum dot. The result shows that the effect of magnetic field strength is more strongly dependent on the nonlinear optical property in a low-dimensional semiconductor system.

关键词： oscillator strength exciton quantum dot