Phonon sidebands in the electrolumiescence(EL) spectra of InGaN/GaN multiple quantum well blue light emitting diodes are investigated. S-shaped injection current dependence of the energy spacing(ES) between the zero-p...Phonon sidebands in the electrolumiescence(EL) spectra of InGaN/GaN multiple quantum well blue light emitting diodes are investigated. S-shaped injection current dependence of the energy spacing(ES) between the zero-phonon and first-order phonon-assisted luminescence lines is observed in a temperature range of 100–150 K.The S-shape is suppressed with increasing temperature from 100 to 150 K, and vanishes at temperature above200 K. The S-shaped injection dependence of ES at low temperatures could be explained by the three stages of carrier dynamics related to localization states:(i) carrier relaxation from shallow into deep localization states,(ii) band filling of shallow and deep localization states, and(iii) carrier overflow from deep to shallow localization states and to higher energy states. The three stages show strong temperature dependence. It is proposed that the fast change of the carrier lifetime with temperature is responsible for the suppression of S-shaped feature.The proposed mechanisms reveal carrier recombination dynamics in the EL of InGaN/GaN MQWs at various injection current densities and temperatures.展开更多
Two basic types of depolarization mechanisms, carrier-carrier （CC） and carrier-phonon （CP） scattering, are investigated in optically excited bulk semiconductors （3D）, in which the existence of the transverse rel...Two basic types of depolarization mechanisms, carrier-carrier （CC） and carrier-phonon （CP） scattering, are investigated in optically excited bulk semiconductors （3D）, in which the existence of the transverse relaxation time is proven based on the vector property of the interband transition matrix elements. The dephasing rates for both CC and CP scattering are determined to be equal to one half of the total scattering-rate-integrals weighted by the factors （1 -cos χ）, where χ are the scattering angles. Analytical expressions of the polarization dephasing due to CC scattering are established by using an uncertainty broadening approach, and analytical ones due to both the polar optical-phonon and non-polar deformation potential scattering （including inter-valley scattering） are also presented by using the sharp spectral functions in the dephasing rate calculations. These formulas, which reveal the trivial role of the Coulomb screening effect in the depolarization processes, are used to explain the experimental results at hand and provide a clear physical picture that is difficult to extract from numerical treatments.展开更多
Lead halide perovskites have some unique properties which are very promising for optoelectronic applications such as solar cells. LEDs and lasers. One important and expected application of perovskite halide semiconduc...Lead halide perovskites have some unique properties which are very promising for optoelectronic applications such as solar cells. LEDs and lasers. One important and expected application of perovskite halide semiconductors is solar cell operation including hot carriers. This advanced solar cell concept allows overcoming the Shockley-Queisser efficiency limit, thereby achieving energy conversion efficiency as high as 66% by extracting hot carriers. Understanding ultrafast photoexcited carrier dynamics and extraction in lead halide perovskites is crucial for these applications. Here, we clarify the hot carrier cooling and transfer dynamics in all-inorganic cesium lead iodide （CsPbI3） perovskite using transient absorption spectroscopy and Al2O3, poly（3-hexylthiophene-2,5-diyl） （P3HT） and TiO2 as selective contacts. We find that slow hot carrier cooling occurs on a timescale longer than 10 ps in the cases of CsPbI3/AI203 and CsPbI3/TiO2, which is attributed to hot phonon bottleneck for the high photoexcited carrier density. An efficient ultrafast hole transfer from CsPbI3 to the P3HT hole extracting layer is observed. These results suggest that hot holes can be extracted by appropriate selective contacts before energy dissipation into the halide perovskite lattice and that CsPbl3 has a potential for hot carrier solar cell applications.展开更多
We investigate the effects of pre-stress and surface tension on the electron–acoustic phonon scattering rate and the mobility of rectangular silicon nanowires. With the elastic theory and the interaction Hamiltonian ...We investigate the effects of pre-stress and surface tension on the electron–acoustic phonon scattering rate and the mobility of rectangular silicon nanowires. With the elastic theory and the interaction Hamiltonian for the deformation potential, which considers both the surface energy and the acoustoelastic effects, the phonon dispersion relation for a stressed nanowire under spatial confinement is derived. The subsequent analysis indicates that both surface tension and pre-stress can dramatically change the electron–acoustic phonon interaction. Under a negative（positive） surface tension and a tensile（compressive） pre-stress, the electron mobility is reduced（enhanced） due to the decrease（increase） of the phonon energy as well as the deformation-potential scattering rate. This study suggests an alternative approach based on the strain engineering to tune the speed and the drive current of low-dimensional electronic devices.展开更多
The dynamical process of charge injection from metal electrode to a nondegenerate polymer in a metal/polythiophene （PT）/metal structure has been investigated by using a nonadiabatic dynamic approach. It is found tha...The dynamical process of charge injection from metal electrode to a nondegenerate polymer in a metal/polythiophene （PT）/metal structure has been investigated by using a nonadiabatic dynamic approach. It is found that the injected charges form wave packets due to the strong electron-lattice interaction in PT. We demonstrate that the dynamical formation of the wave packet sensitively depends on the strength of applied voltage, the electric field, and the contact between PT and electrode. At a strength of the electric field more than 3.0 × 10^4 V/cm, the carriers can be ejected from the PT into the right electrode. At an electric field more than 3.0 × 10^5 V/cm, the wave packet cannot form while it moves rapidly to the right PT/metal interface. It is shown that the ejected quantity of charge is noninteger.展开更多
Study of spectral dependences of absorption coefficient at the region of absorption by free carriers shows that the introduction of radiation defects in n-GaP crystals leads to the appearance of additional scattering ...Study of spectral dependences of absorption coefficient at the region of absorption by free carriers shows that the introduction of radiation defects in n-GaP crystals leads to the appearance of additional scattering besides of traditional ones. A new scattering mechanism on “frozen” phonons (deformation localized near the radiation defects) is suggested and its behavior in experimental and theoretical aspects taking into account Х1с-Х3с transitions at the scattering process has been studied. It was shown that the increase of “frozen” phonons’ concentration results to the growth of this mechanism contribution in the whole scattering and the absorption coefficient by free carriers is described approximately by low α ~ ω-r, where -1/2 ≤ r ≤ 7/2. Suggested scattering mechanism allows explaining qualitatively the decrease of r. It was established that the dis- ordered by irradiation region effectively decreases the concentration of free carriers, but being a region of increased resistivity, it influences the scattering slightly even at the actual quantum region .展开更多
Intrinsic broadband photoluminescence(PL)of self-trapped excitons(STEs)are systematically studied in lead-free double perovskite nanocrystals(NCs).It is clarified that bandgap(direct/indirect)has important influence o...Intrinsic broadband photoluminescence(PL)of self-trapped excitons(STEs)are systematically studied in lead-free double perovskite nanocrystals(NCs).It is clarified that bandgap(direct/indirect)has important influence on the PL properties of STEs:indirect bandgap NCs exhibit strong exciton-phonon coupling which results in non-radiative STEs,while direct bandgap NCs exhibit moderate exciton-phonon coupling,inducing bright STE PL.Furthermore,by alloying K+and Li+ions in Cs2AgInCl6 NCs,the NCs exhibit broadband white-light emission.Charge-carrier dynamics study indicates that the efficient white-light emission originates from the further suppressed non-radiative processes of the STEs in the direct bandgap structure.This work may deepen the understanding of STEs and guide the design of highperformance lead-free perovskites.展开更多
Organic-inorganic hybrid two dimensional(2D)lead halide perovskites(LHPs)are tunable quantum wells that exhibit a set of intriguing structural and physical properties including soft and dynamic lattices,organic-inorga...Organic-inorganic hybrid two dimensional(2D)lead halide perovskites(LHPs)are tunable quantum wells that exhibit a set of intriguing structural and physical properties including soft and dynamic lattices,organic-inorganic epitaxial heterointerfaces,quantum and dielectric confinements,strong light-matter interactions,and large spin-orbit coupling,which enable promising perspectives for optoelectronics,ferroelectrics,and spintronics.While the properties of 2D LHPs bear some resemblance of the3D LHPs,they are often drastically altered due to the reduced dimensionality and the complex interactions between organic and inorganic components.In this review,we discuss the influences of the reduced dimensionality and the organic-inorganic interplays on the structural stability and distortion of the inorganic lattices,inversion symmetry of the crystal structure,electronic band structures,excitonic physics,and carrier-phonon interactions in 2D LHPs.An emphasis is placed on the relationships between the crystal structures and photophysical properties.Future perspectives on the opportunities of hybrid quantum wells are provided.展开更多
基金Supported by the National Science Foundation for Young Scientists of China under Grant No 11604137the Jiangxi Province Postdoctoral Science Foundation Funded Project under Grant No 2015KY32the State Key Program of Research and Development of China under Grant Nos 2016YFB040060 and 2016YFB0400601
文摘Phonon sidebands in the electrolumiescence(EL) spectra of InGaN/GaN multiple quantum well blue light emitting diodes are investigated. S-shaped injection current dependence of the energy spacing(ES) between the zero-phonon and first-order phonon-assisted luminescence lines is observed in a temperature range of 100–150 K.The S-shape is suppressed with increasing temperature from 100 to 150 K, and vanishes at temperature above200 K. The S-shaped injection dependence of ES at low temperatures could be explained by the three stages of carrier dynamics related to localization states:(i) carrier relaxation from shallow into deep localization states,(ii) band filling of shallow and deep localization states, and(iii) carrier overflow from deep to shallow localization states and to higher energy states. The three stages show strong temperature dependence. It is proposed that the fast change of the carrier lifetime with temperature is responsible for the suppression of S-shaped feature.The proposed mechanisms reveal carrier recombination dynamics in the EL of InGaN/GaN MQWs at various injection current densities and temperatures.
基金Project supported by the State Key Program of Basic Research of China （Grant No 2001CB309307）, and the National Natural Science Foundation of China （Grant Nos 10474105, 10274107 and 10334050）.
文摘Two basic types of depolarization mechanisms, carrier-carrier （CC） and carrier-phonon （CP） scattering, are investigated in optically excited bulk semiconductors （3D）, in which the existence of the transverse relaxation time is proven based on the vector property of the interband transition matrix elements. The dephasing rates for both CC and CP scattering are determined to be equal to one half of the total scattering-rate-integrals weighted by the factors （1 -cos χ）, where χ are the scattering angles. Analytical expressions of the polarization dephasing due to CC scattering are established by using an uncertainty broadening approach, and analytical ones due to both the polar optical-phonon and non-polar deformation potential scattering （including inter-valley scattering） are also presented by using the sharp spectral functions in the dephasing rate calculations. These formulas, which reveal the trivial role of the Coulomb screening effect in the depolarization processes, are used to explain the experimental results at hand and provide a clear physical picture that is difficult to extract from numerical treatments.
基金supported by the CREST program of Japan Science and Technology Agency(JST)supported by KAKENHI from the Japan Society for the Promotion of Science(JSPS)under the Grant-in-Aid for Young Scientists B(Grant Number JP16K17947)
文摘Lead halide perovskites have some unique properties which are very promising for optoelectronic applications such as solar cells. LEDs and lasers. One important and expected application of perovskite halide semiconductors is solar cell operation including hot carriers. This advanced solar cell concept allows overcoming the Shockley-Queisser efficiency limit, thereby achieving energy conversion efficiency as high as 66% by extracting hot carriers. Understanding ultrafast photoexcited carrier dynamics and extraction in lead halide perovskites is crucial for these applications. Here, we clarify the hot carrier cooling and transfer dynamics in all-inorganic cesium lead iodide （CsPbI3） perovskite using transient absorption spectroscopy and Al2O3, poly（3-hexylthiophene-2,5-diyl） （P3HT） and TiO2 as selective contacts. We find that slow hot carrier cooling occurs on a timescale longer than 10 ps in the cases of CsPbI3/AI203 and CsPbI3/TiO2, which is attributed to hot phonon bottleneck for the high photoexcited carrier density. An efficient ultrafast hole transfer from CsPbI3 to the P3HT hole extracting layer is observed. These results suggest that hot holes can be extracted by appropriate selective contacts before energy dissipation into the halide perovskite lattice and that CsPbl3 has a potential for hot carrier solar cell applications.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11472243,11302189,and 11321202)the Doctoral Fund of Ministry of Education of China(Grant No.20130101120175)+1 种基金the Zhejiang Provincial Qianjiang Talent Program,China(Grant No.QJD1202012)the Educational Commission of Zhejiang Province,China(Grant No.Y201223476)
文摘We investigate the effects of pre-stress and surface tension on the electron–acoustic phonon scattering rate and the mobility of rectangular silicon nanowires. With the elastic theory and the interaction Hamiltonian for the deformation potential, which considers both the surface energy and the acoustoelastic effects, the phonon dispersion relation for a stressed nanowire under spatial confinement is derived. The subsequent analysis indicates that both surface tension and pre-stress can dramatically change the electron–acoustic phonon interaction. Under a negative（positive） surface tension and a tensile（compressive） pre-stress, the electron mobility is reduced（enhanced） due to the decrease（increase） of the phonon energy as well as the deformation-potential scattering rate. This study suggests an alternative approach based on the strain engineering to tune the speed and the drive current of low-dimensional electronic devices.
基金Project supported by the State Key Program of National Natural Science of China (Grant Nos 10474056 and 10574082)the Natural Science Foundation of Shandong Province (Grant No Z2005A01)
文摘The dynamical process of charge injection from metal electrode to a nondegenerate polymer in a metal/polythiophene （PT）/metal structure has been investigated by using a nonadiabatic dynamic approach. It is found that the injected charges form wave packets due to the strong electron-lattice interaction in PT. We demonstrate that the dynamical formation of the wave packet sensitively depends on the strength of applied voltage, the electric field, and the contact between PT and electrode. At a strength of the electric field more than 3.0 × 10^4 V/cm, the carriers can be ejected from the PT into the right electrode. At an electric field more than 3.0 × 10^5 V/cm, the wave packet cannot form while it moves rapidly to the right PT/metal interface. It is shown that the ejected quantity of charge is noninteger.
文摘Study of spectral dependences of absorption coefficient at the region of absorption by free carriers shows that the introduction of radiation defects in n-GaP crystals leads to the appearance of additional scattering besides of traditional ones. A new scattering mechanism on “frozen” phonons (deformation localized near the radiation defects) is suggested and its behavior in experimental and theoretical aspects taking into account Х1с-Х3с transitions at the scattering process has been studied. It was shown that the increase of “frozen” phonons’ concentration results to the growth of this mechanism contribution in the whole scattering and the absorption coefficient by free carriers is described approximately by low α ~ ω-r, where -1/2 ≤ r ≤ 7/2. Suggested scattering mechanism allows explaining qualitatively the decrease of r. It was established that the dis- ordered by irradiation region effectively decreases the concentration of free carriers, but being a region of increased resistivity, it influences the scattering slightly even at the actual quantum region .
基金supported by the National Natural Science Foundation of China(21533010,21525315)the National Key Research and Development Program of China(2017YFA0204800)DICP DMTO201601,DICP ZZBS201703,and the Science Challenging Program(JCKY2016212A501).
文摘Intrinsic broadband photoluminescence(PL)of self-trapped excitons(STEs)are systematically studied in lead-free double perovskite nanocrystals(NCs).It is clarified that bandgap(direct/indirect)has important influence on the PL properties of STEs:indirect bandgap NCs exhibit strong exciton-phonon coupling which results in non-radiative STEs,while direct bandgap NCs exhibit moderate exciton-phonon coupling,inducing bright STE PL.Furthermore,by alloying K+and Li+ions in Cs2AgInCl6 NCs,the NCs exhibit broadband white-light emission.Charge-carrier dynamics study indicates that the efficient white-light emission originates from the further suppressed non-radiative processes of the STEs in the direct bandgap structure.This work may deepen the understanding of STEs and guide the design of highperformance lead-free perovskites.
基金supported by the National Natural Science Foundation of China(22271006)Peking University and Beijing National Laboratory for Molecular Sciences for startup funding。
文摘Organic-inorganic hybrid two dimensional(2D)lead halide perovskites(LHPs)are tunable quantum wells that exhibit a set of intriguing structural and physical properties including soft and dynamic lattices,organic-inorganic epitaxial heterointerfaces,quantum and dielectric confinements,strong light-matter interactions,and large spin-orbit coupling,which enable promising perspectives for optoelectronics,ferroelectrics,and spintronics.While the properties of 2D LHPs bear some resemblance of the3D LHPs,they are often drastically altered due to the reduced dimensionality and the complex interactions between organic and inorganic components.In this review,we discuss the influences of the reduced dimensionality and the organic-inorganic interplays on the structural stability and distortion of the inorganic lattices,inversion symmetry of the crystal structure,electronic band structures,excitonic physics,and carrier-phonon interactions in 2D LHPs.An emphasis is placed on the relationships between the crystal structures and photophysical properties.Future perspectives on the opportunities of hybrid quantum wells are provided.
