Based on the framework of the effective-mass approximation, the ionized acceptor bound exciton （A- X） binding energy and the emission wavelength are investigated for a cylindrical wurtzite （WZ） GaN/A1x Ga1-xN quan...Based on the framework of the effective-mass approximation, the ionized acceptor bound exciton （A- X） binding energy and the emission wavelength are investigated for a cylindrical wurtzite （WZ） GaN/A1x Ga1-xN quantum dot （QD） with finite potential barriers by means of a variational method. Numerical results show that the binding energy and the emission wavelength highly depend on the QD size, the position of the ionized acceptor and the Al composition x of the barrier material AIxGal-xN. The binding energy and the emission wavelength are larger when the acceptor is located in the vicinity of the left interface of the QD. In particular, the binding energy of （ A-, X） complex is insensitive to the dot height when the acceptor is located at the left boundary of the QD. The ionized acceptor bound exciton binding energy and the emission wavelength are both increased if Al composition x is increased.展开更多
Quasi-two dimensional(2D)perovskites have emerged as a promising class of materials due to their remarkable photoluminescence efficiency,which stems from their exceptionally high exciton binding energies.The spatial c...Quasi-two dimensional(2D)perovskites have emerged as a promising class of materials due to their remarkable photoluminescence efficiency,which stems from their exceptionally high exciton binding energies.The spatial confinement of excitons within smaller grain sizes could enhance the formation of biexcitons leading to higher radiative recombination efficiency.However,the synthesis of high-quality quasi-2D perovskite thin films with controllable grain sizes remains a challenging task.In this study,we present a facile method for achieving quasi-2D perovskite thin films with controllable grain sizes ranging from 500 to 900 nm.This is accomplished by intermediate phase engineering during the film fabrication process.Our results demonstrate that quasi-2D perovskite films with smaller grain sizes exhibit more efficient bound exciton generation and a reduced stimulated emission threshold down to 15.89µJ cm^(−2).Furthermore,femtosecond transient absorption measurements reveal that the decay time of bound excitons is shorter in quasi-2D perovskites with smaller grain sizes compared to that of those with larger grains at the same pump density,which is 230.5 ps.This observation suggests a more efficient exciton recombination process in the smaller grain size regime.Our findings would offer a promising approach for the development of efficient bound exciton lasers.展开更多
Within the framework of the effective-mass approximation and the dipole approximation, considering the three-dimensional confinement of the electron and hole and the strong bulk-in electric field （BEF） in strained w...Within the framework of the effective-mass approximation and the dipole approximation, considering the three-dimensional confinement of the electron and hole and the strong bulk-in electric field （BEF） in strained wurtzite ZnO/Mgo.25Zno.750 quantum dots （QDs）, the optical properties of ionized donor-bound excitons （D^＋, X） are investigated theoretically using a variational method. The computations are performed in the case of finite band offset. Numerical results indicate that the optical properties of （D^＋, X） complexes sensitively depend on the donor position, the QD size and the BEF. The binding energy of （D^＋, X） complexes is larger when the donor is located in the vicinity of the left interface of the QDs, and it decreases with increasing QD size. The oscillator strength reduces with an increase in the dot height and increases with an increase in the dot radius. Furthermore, when the QD size decreases, the absorption peak intensity shows a marked increment, and the absorption coefficient peak has a blueshift. The strong BEF causes a redshift of the absorption coefficient peak and causes the absorption peak intensity to decrease remarkably. The physical reasons for these relationships have been analyzed in depth.展开更多
In the effective-mass approximation, using a simple two-parameter wave function and a one-dimensional （ID） equivalent potential model, we calculate variationally the binding energy of an exciton bound to a neutral d...In the effective-mass approximation, using a simple two-parameter wave function and a one-dimensional （ID） equivalent potential model, we calculate variationally the binding energy of an exciton bound to a neutral donor （D^0, X） in finite GaAs-AIxGa1-xAs quantum well wires （QWWs）. At the wire width of 25 A, the binding energy has a peak value, which is also at the position of the peak of the exciton binding energy, and the center-of-mass wave functions of excitons reaches the most centralized distribution. In addition, the changing tendency of the average interparticle distance as the wire width is reverse to that of the binding energy.展开更多
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 G...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.展开更多
Time-resolved photoluminescence （TRPL） was applied to investigate the transient process in GaP1-xNx （x = 0.12%） alloy. The filling, transferring and decay processes among nitrogen pairs are directly observed. The ...Time-resolved photoluminescence （TRPL） was applied to investigate the transient process in GaP1-xNx （x = 0.12%） alloy. The filling, transferring and decay processes among nitrogen pairs are directly observed. The NN4 pair, either not present or only a small obscure peak under a proper excitation condition in the steady-state photoluminescence spectrum, is well resolved by TRPL.展开更多
A brief history of the impurity theories in semiconductors is provided. A bound exciton model is proposed for both donor-and acceptor-like impurities and point defects, which offers a unified understanding for ＂shal...A brief history of the impurity theories in semiconductors is provided. A bound exciton model is proposed for both donor-and acceptor-like impurities and point defects, which offers a unified understanding for ＂shallow＂ and ＂deep＂impurities and point defects. The underlying physics of computational results using different density-functional theorybased approaches are discussed and interpreted in the framework of the bound exciton model.展开更多
基金Supported by Technology Projects of the Education Bureau of Fujian Province umder Grant No. JK2009038
文摘Based on the framework of the effective-mass approximation, the ionized acceptor bound exciton （A- X） binding energy and the emission wavelength are investigated for a cylindrical wurtzite （WZ） GaN/A1x Ga1-xN quantum dot （QD） with finite potential barriers by means of a variational method. Numerical results show that the binding energy and the emission wavelength highly depend on the QD size, the position of the ionized acceptor and the Al composition x of the barrier material AIxGal-xN. The binding energy and the emission wavelength are larger when the acceptor is located in the vicinity of the left interface of the QD. In particular, the binding energy of （ A-, X） complex is insensitive to the dot height when the acceptor is located at the left boundary of the QD. The ionized acceptor bound exciton binding energy and the emission wavelength are both increased if Al composition x is increased.
基金supported by the National Natural Science Foundation of China(U21A20496 and 12104334)the Fund Program for the Scientific Activities of Selected Returned Overseas Professionals in Shanxi Province(20230011)+5 种基金the Research Program Supported by ShanxiZheda Institute of Advanced Materials and Chemical Engineering(2022SXTD020)the Central Government Guides Local Funds for Scientific and Technological Development(YDZJSX20231A010)the Natural Science Foundation of Shanxi Province(202203021222102)the State Key Laboratory Program of Quantum Optics and Quantum Optics Devices(KF202306)the support from a research grant(VIL50350)from VILLUM FONDEN,Denmark,the Swedish Research Council(2021-05319)the Swedish foundation of international cooperation in research and higher education(CH2019-8248)。
文摘Quasi-two dimensional(2D)perovskites have emerged as a promising class of materials due to their remarkable photoluminescence efficiency,which stems from their exceptionally high exciton binding energies.The spatial confinement of excitons within smaller grain sizes could enhance the formation of biexcitons leading to higher radiative recombination efficiency.However,the synthesis of high-quality quasi-2D perovskite thin films with controllable grain sizes remains a challenging task.In this study,we present a facile method for achieving quasi-2D perovskite thin films with controllable grain sizes ranging from 500 to 900 nm.This is accomplished by intermediate phase engineering during the film fabrication process.Our results demonstrate that quasi-2D perovskite films with smaller grain sizes exhibit more efficient bound exciton generation and a reduced stimulated emission threshold down to 15.89µJ cm^(−2).Furthermore,femtosecond transient absorption measurements reveal that the decay time of bound excitons is shorter in quasi-2D perovskites with smaller grain sizes compared to that of those with larger grains at the same pump density,which is 230.5 ps.This observation suggests a more efficient exciton recombination process in the smaller grain size regime.Our findings would offer a promising approach for the development of efficient bound exciton lasers.
基金Project supported by the National Natural Science Foundation for Young Scientists of China(No.11102100)the Program for New Century Excellent Talents in Fujian Province University(No.JA14285)the Program for Young Top-Notch Innovative Talents of Fujian Province of China
文摘Within the framework of the effective-mass approximation and the dipole approximation, considering the three-dimensional confinement of the electron and hole and the strong bulk-in electric field （BEF） in strained wurtzite ZnO/Mgo.25Zno.750 quantum dots （QDs）, the optical properties of ionized donor-bound excitons （D^＋, X） are investigated theoretically using a variational method. The computations are performed in the case of finite band offset. Numerical results indicate that the optical properties of （D^＋, X） complexes sensitively depend on the donor position, the QD size and the BEF. The binding energy of （D^＋, X） complexes is larger when the donor is located in the vicinity of the left interface of the QDs, and it decreases with increasing QD size. The oscillator strength reduces with an increase in the dot height and increases with an increase in the dot radius. Furthermore, when the QD size decreases, the absorption peak intensity shows a marked increment, and the absorption coefficient peak has a blueshift. The strong BEF causes a redshift of the absorption coefficient peak and causes the absorption peak intensity to decrease remarkably. The physical reasons for these relationships have been analyzed in depth.
基金The project supported by National Natural Science Foundation of China under Grant No. 10574036, and the Natural Science Foundation of Hebei Province of China under Grant No. A2004000140
文摘In the effective-mass approximation, using a simple two-parameter wave function and a one-dimensional （ID） equivalent potential model, we calculate variationally the binding energy of an exciton bound to a neutral donor （D^0, X） in finite GaAs-AIxGa1-xAs quantum well wires （QWWs）. At the wire width of 25 A, the binding energy has a peak value, which is also at the position of the peak of the exciton binding energy, and the center-of-mass wave functions of excitons reaches the most centralized distribution. In addition, the changing tendency of the average interparticle distance as the wire width is reverse to that of the binding energy.
基金Project supported by the University Grants Commission,India (Grant No.38-8/2009(SR))
文摘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.
基金Supported by the National Natural Science Foundation of China under Grant No 60276002.
文摘Time-resolved photoluminescence （TRPL） was applied to investigate the transient process in GaP1-xNx （x = 0.12%） alloy. The filling, transferring and decay processes among nitrogen pairs are directly observed. The NN4 pair, either not present or only a small obscure peak under a proper excitation condition in the steady-state photoluminescence spectrum, is well resolved by TRPL.
基金supported by ARO/MURI (W911NF-101-0524 monitored by Dr. William Clark)ARO/Electronics (W911NF1610263 monitored by Dr. William Clark and Dr. Michele Gerhold)Bissell Distinguished Professorship at UNCC
文摘A brief history of the impurity theories in semiconductors is provided. A bound exciton model is proposed for both donor-and acceptor-like impurities and point defects, which offers a unified understanding for ＂shallow＂ and ＂deep＂impurities and point defects. The underlying physics of computational results using different density-functional theorybased approaches are discussed and interpreted in the framework of the bound exciton model.
