The hydrogenic donor impurity states and intersubband optical absorption spectra in monolayer transition metal dichalcogenides(ML TMDs) under dielectric environments are theoretically investigated based on a two-dimen...The hydrogenic donor impurity states and intersubband optical absorption spectra in monolayer transition metal dichalcogenides(ML TMDs) under dielectric environments are theoretically investigated based on a two-dimensional(2D)nonorthogonal associated Laguerre basis set. The 2D quantum confinement effect together with the strongly reduced dielectric screening results in the strong attractive Coulomb potential between electron and donor ion, with exceptionally large impurity binding energy and huge intersubband oscillator strength. These lead to the strong interaction of the electron with light in a 2D regime. The intersubband optical absorption spectra exhibit strong absorption lines of the non-hydrogenic Rydberg series in the mid-infrared range of light. The strength of the Coulomb potential can be controlled by changing the dielectric environment. The electron affinity difference leads to charge transfer between ML TMD and the dielectric environment, generating the polarization-electric field in ML TMD accompanied by weakening the Coulomb interaction strength. The larger the dielectric constant of the dielectric environment, the more the charge transfer is, accompanied by the larger polarization-electric field and the stronger dielectric screening. The dielectric environment is shown to provide an efficient tool to tune the wavelength and output of the mid-infrared intersubband devices based on ML TMDs.展开更多
Some realizable structures of double parabolic quantum wells（DPQWs） consisting of Al_xGa_（1-x）As/Al_yGa_（1-y）As are constructed to discuss theoretically the optical absorption due to the intersubband transition ...Some realizable structures of double parabolic quantum wells（DPQWs） consisting of Al_xGa_（1-x）As/Al_yGa_（1-y）As are constructed to discuss theoretically the optical absorption due to the intersubband transition of electrons for both symmetric and asymmetric cases with three energy levels of conduction bands. The electronic states in these structures are obtained using a finite element difference method. Based on a compact density matrix approach, the optical absorption induced by intersubband transition of electrons at room temperature is discussed. The results reveal that the peak positions and heights of intersubband optical absorption coefficients（IOACs） of DPQWs are sensitive to the barrier thickness, depending on Al component. Furthermore, external electric fields result in the decrease of peak, and play an important role in the blue shifts of absorption spectra due to electrons excited from ground state to the first and second excited states. It is found that the peaks of IOACs are smaller in asymmetric DPQWs than in symmetric ones. The results also indicate that the adjustable extent of incident photon energy for DPQW is larger than for a square one of a similar size. Our results are helpful in experiments and device fabrication.展开更多
Based on the effective mass approximation, the Schrodinger equation and Poisson equation in GaAs/AlGaAs multi-quantum wells(MQWs) are self-consistently solved to obtain the wave functions and energy levels of electron...Based on the effective mass approximation, the Schrodinger equation and Poisson equation in GaAs/AlGaAs multi-quantum wells(MQWs) are self-consistently solved to obtain the wave functions and energy levels of electrons in the conduction band for the ground first excited state by considering a lateral electric field(LEF). Then, the effects of size, ternary mixed crystal, doping concentration, and temperature on linear and nonlinear intersubband optical absorption coefficients(IOACs), and refractive index changes(RICs) due to the transition between ground states and the first excited states of electrons are discussed based on Fermi’s golden rule. The results show that, under a fixed LEF, with increase of A1 composition and doping concentration, the IOACs produce a red shift. With increases of both widths of the wells and barriers IOACs appear as blue shifts and their amplitudes increase, but the barrier width change is much more important to affect nonlinear IOACs, whereas increasing the temperature results in a blue shift first and then a red shift of IOACs. When the other parameters are fixed but there is an increase in the LEF, IOACs occur with a blue shift, and the RICs have similar properties.展开更多
Effects of LO-phonon contribution on the electronic and the optical properties are investigated in a Cdo.sZno.2 Se/ZnSe quantum dot in the presence of magnetic field strength. The magneto-polaron induced hydro- genic ...Effects of LO-phonon contribution on the electronic and the optical properties are investigated in a Cdo.sZno.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.展开更多
The emerging two-dimensional(2D)platinum disulfide(PtS_(2))has driven increasing attentions due to its high electron mobility,good air-stability,and strong interlayer interaction which leads to a widely tunable electr...The emerging two-dimensional(2D)platinum disulfide(PtS_(2))has driven increasing attentions due to its high electron mobility,good air-stability,and strong interlayer interaction which leads to a widely tunable electronic structure.However,a detailed study on its covalent-like layer-dependent properties remains infant.Herein,we demonstrate the successful production of ultrathin 1T-PtS_(2) ribbons with thickness centralized almost at monolayer 1L-4L and large domain size up to 210 μm on Au foils using chemical vapor deposition(CVD)technique,which enables macro-and microscopic study of its extraordinary layer-dependent features with precise control of the number of layers.Using electron energy loss spectroscopy(EELS)and optical pump-probe spectroscopy(OPPS),we reveal that both the electron and ultrafast optical absorption signals of the as-grown 2D PtS_(2) show strong nonlinear layer-dependent responses which manifest discriminated transition in 1L-4L PtS_(2) ribbons.The layer-dependent nonlinear response of 2D PtS_(2) can be well interpreted in the frame of calculated electron and phonon structures.These achievements offer a platform for successfully fabricating large-sized ultrathin 2D PtS_(2) and facilitating our knowledge about its electronic and optoelectronic properties.展开更多
The thermoelectric compound TiS2 is studied by using the full-potential linearized augmented plane-wave method on the density functional theory with the generalized gradient approximation （GGA） as well as the on-sit...The thermoelectric compound TiS2 is studied by using the full-potential linearized augmented plane-wave method on the density functional theory with the generalized gradient approximation （GGA） as well as the on-site Coulomb interaction correction （＋U）. The Seebeck coefficient of TiS2 is calculated based on the electronic structure obtained within the GGA under the consideration of the on-site Coulomb interaction. The calculated Seebeck coefficient at 300K shows that Coulomb interaction U in the range of 4.97-5.42eV is important to reproduce the experimental data. The obtained energy gap Eg around 0.05 eV indicates that TiS2 is an indirect narrow-gap semiconductor.展开更多
文摘The hydrogenic donor impurity states and intersubband optical absorption spectra in monolayer transition metal dichalcogenides(ML TMDs) under dielectric environments are theoretically investigated based on a two-dimensional(2D)nonorthogonal associated Laguerre basis set. The 2D quantum confinement effect together with the strongly reduced dielectric screening results in the strong attractive Coulomb potential between electron and donor ion, with exceptionally large impurity binding energy and huge intersubband oscillator strength. These lead to the strong interaction of the electron with light in a 2D regime. The intersubband optical absorption spectra exhibit strong absorption lines of the non-hydrogenic Rydberg series in the mid-infrared range of light. The strength of the Coulomb potential can be controlled by changing the dielectric environment. The electron affinity difference leads to charge transfer between ML TMD and the dielectric environment, generating the polarization-electric field in ML TMD accompanied by weakening the Coulomb interaction strength. The larger the dielectric constant of the dielectric environment, the more the charge transfer is, accompanied by the larger polarization-electric field and the stronger dielectric screening. The dielectric environment is shown to provide an efficient tool to tune the wavelength and output of the mid-infrared intersubband devices based on ML TMDs.
基金Project supported by the National Natural Science Foundation of China(Grant No.61274098)
文摘Some realizable structures of double parabolic quantum wells（DPQWs） consisting of Al_xGa_（1-x）As/Al_yGa_（1-y）As are constructed to discuss theoretically the optical absorption due to the intersubband transition of electrons for both symmetric and asymmetric cases with three energy levels of conduction bands. The electronic states in these structures are obtained using a finite element difference method. Based on a compact density matrix approach, the optical absorption induced by intersubband transition of electrons at room temperature is discussed. The results reveal that the peak positions and heights of intersubband optical absorption coefficients（IOACs） of DPQWs are sensitive to the barrier thickness, depending on Al component. Furthermore, external electric fields result in the decrease of peak, and play an important role in the blue shifts of absorption spectra due to electrons excited from ground state to the first and second excited states. It is found that the peaks of IOACs are smaller in asymmetric DPQWs than in symmetric ones. The results also indicate that the adjustable extent of incident photon energy for DPQW is larger than for a square one of a similar size. Our results are helpful in experiments and device fabrication.
基金Project supported by the National Natural Science Foundation of China(No.61764012)
文摘Based on the effective mass approximation, the Schrodinger equation and Poisson equation in GaAs/AlGaAs multi-quantum wells(MQWs) are self-consistently solved to obtain the wave functions and energy levels of electrons in the conduction band for the ground first excited state by considering a lateral electric field(LEF). Then, the effects of size, ternary mixed crystal, doping concentration, and temperature on linear and nonlinear intersubband optical absorption coefficients(IOACs), and refractive index changes(RICs) due to the transition between ground states and the first excited states of electrons are discussed based on Fermi’s golden rule. The results show that, under a fixed LEF, with increase of A1 composition and doping concentration, the IOACs produce a red shift. With increases of both widths of the wells and barriers IOACs appear as blue shifts and their amplitudes increase, but the barrier width change is much more important to affect nonlinear IOACs, whereas increasing the temperature results in a blue shift first and then a red shift of IOACs. When the other parameters are fixed but there is an increase in the LEF, IOACs occur with a blue shift, and the RICs have similar properties.
文摘Effects of LO-phonon contribution on the electronic and the optical properties are investigated in a Cdo.sZno.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.
基金The work was supported by the National Natural Science Foundation of China(Nos.51991344,51991340,11774354,51727806,61988102,11974156,12174398,and 12104206)Guangdong International Science Collaboration Project(No.2019A050510001)+2 种基金Guangdong Innovative and Entrepreneurial Research Team Program(No.2019ZT08C044)Shenzhen Science and Technology Program(Nos.KQTD20190929173815000 and 20200925161102001)the Science,Technology and Innovation Commission of Shenzhen Municipality(No.ZDSYS20190902092905285)。
文摘The emerging two-dimensional(2D)platinum disulfide(PtS_(2))has driven increasing attentions due to its high electron mobility,good air-stability,and strong interlayer interaction which leads to a widely tunable electronic structure.However,a detailed study on its covalent-like layer-dependent properties remains infant.Herein,we demonstrate the successful production of ultrathin 1T-PtS_(2) ribbons with thickness centralized almost at monolayer 1L-4L and large domain size up to 210 μm on Au foils using chemical vapor deposition(CVD)technique,which enables macro-and microscopic study of its extraordinary layer-dependent features with precise control of the number of layers.Using electron energy loss spectroscopy(EELS)and optical pump-probe spectroscopy(OPPS),we reveal that both the electron and ultrafast optical absorption signals of the as-grown 2D PtS_(2) show strong nonlinear layer-dependent responses which manifest discriminated transition in 1L-4L PtS_(2) ribbons.The layer-dependent nonlinear response of 2D PtS_(2) can be well interpreted in the frame of calculated electron and phonon structures.These achievements offer a platform for successfully fabricating large-sized ultrathin 2D PtS_(2) and facilitating our knowledge about its electronic and optoelectronic properties.
基金Supported by the National Science Foundation of China under Grant Nos 10504036 and 50472097, the Special Funds for Major State Basic Research Project of China under Grant No 2005CB623603, the Knowledge Innovation Programme of Chinese Academy of Sciences, and Director Grants of Hefei Institutes of Physical Sciences.
文摘The thermoelectric compound TiS2 is studied by using the full-potential linearized augmented plane-wave method on the density functional theory with the generalized gradient approximation （GGA） as well as the on-site Coulomb interaction correction （＋U）. The Seebeck coefficient of TiS2 is calculated based on the electronic structure obtained within the GGA under the consideration of the on-site Coulomb interaction. The calculated Seebeck coefficient at 300K shows that Coulomb interaction U in the range of 4.97-5.42eV is important to reproduce the experimental data. The obtained energy gap Eg around 0.05 eV indicates that TiS2 is an indirect narrow-gap semiconductor.
