Hydrogen-like donor impurity states in symmetric triangular quantum wells are investigated by using a variational method.Both the effects of the variable effective mass of electrons and the spatially dependent dielect...Hydrogen-like donor impurity states in symmetric triangular quantum wells are investigated by using a variational method.Both the effects of the variable effective mass of electrons and the spatially dependent dielectric constant are considered in the calculation.The numerical results show that the binding energy depends on not only the effective mass and dielectric constant but also the spatial distribution of electron probability density.The binding energies of donor states get the maximums at the well-center.The results are also compared with those obtained in parabolic and square wells.It is seen that the triangular well support the highest binding energies for donor states.展开更多
A novel double buffer of Eu2CuO4 (ECO)/YSZ (yttrium-stabilized zirconia) was developed for growing YBa2Cu3Oy (YBCO) thin films on Si substrates. In these films, the severe reaction between Si and YBCO is blocked by th...A novel double buffer of Eu2CuO4 (ECO)/YSZ (yttrium-stabilized zirconia) was developed for growing YBa2Cu3Oy (YBCO) thin films on Si substrates. In these films, the severe reaction between Si and YBCO is blocked by the first YSZ layer, whereas, the degradation of crystallinity and superconductivity in the grown YBCO is greatly improved by the second ECO layer. Such an ECO material possesses a very stable 214-T’ structure and excellent compatibilities with YBCO and YSZ. The result shows that the epitaxy and crystallinity of YBCO deposited on Si could be considerably enhanced by using the ECO/YSZ double buffer. The grown films are characterized by high-resolution X-ray diffraction, grazing incidence X-ray reflection, and transmission electron microscopy (TEM), respectively. It is found that well defined interfaces are formed at YBCO/ECO/YSZ boundaries. No immediate layer could be seen. The defect density in all grown layers is kept at a lower level. The YBCO film surface turns out to be very smooth. These films have full superconducting transitions above 88 K and high current carrying capacity at 77 K. The successful growth of highly epitaxial YBCO thin films on silicon with ECO/YSZ buffer, demonstrate the advantages of such a double buffer structure.展开更多
The growth front evolution of GaN thin films deposited on sapphire substrate by hydride vapor phase epitaxity has been studied with atomic force microscope. The evolution of the surface morphology presents four featur...The growth front evolution of GaN thin films deposited on sapphire substrate by hydride vapor phase epitaxity has been studied with atomic force microscope. The evolution of the surface morphology presents four features of stage with the growth process. In initial growth stage, the surface is granular, and the typical grain diameter is about 250 nm for t =0.1 min. 3D growth plays a key role before the films come up to full coalescence, which causes a rough surface. After 0. 1 min the growth dimension decreases with the increase of lateral over growth, the surface roughness obviously decreases. From 0.4 min to 3 rain, the growth front roughness increases gradually, and the evolution of the surface roughness exhibits the characteristics of self-affined fractal. Beyond 3 min, the root-mean-square decreases gradually, which means the deposition behavior from hyper-2D growth gradually turns into layer growth mode with the increase of growth time.展开更多
Photoluminescence spectra were used to characterize the boron-doped Si layers grown by molecular beam epitaxy using HBO2 as the doping source. The influence of boron doping concentration on the dislocation-related pho...Photoluminescence spectra were used to characterize the boron-doped Si layers grown by molecular beam epitaxy using HBO2 as the doping source. The influence of boron doping concentration on the dislocation-related photoluminescence spectra of molecular beam epitaxy Si layers annealed at 900℃ was studied with different doping concentrations and growth temperature. The broad photoluminescence band（from 0.75eV to 0.90eV） including D1 and D2 bands was associated with high boron doping concentration in the samples, while D3 and D4 bands might be related to oxygen precipitates.展开更多
Transparent conducting oxides （TCOs） have attracted in- tensive attention because of their broad application in pho- toelectric devices such as solar cells, light-emitting diodes, and flat-panel displays. Current TC...Transparent conducting oxides （TCOs） have attracted in- tensive attention because of their broad application in pho- toelectric devices such as solar cells, light-emitting diodes, and flat-panel displays. Current TCOs used in industry, including tin （IV） oxide （SnOz）, indium oxide （In203）, indium tin oxide （ITO）, and zinc oxide （ZnO）, are primarily n-type semiconductors [1-3]. Suitable p-type TCOs are still being researched. In the past several decades, delafossite-type compounds CuMO2 （M = Cr, A1, Ga, Fe, Sc, Y） as well as NiO, Cr203, and MoO3 have been extensively studied as potential p-type TCO candidates [4-8].展开更多
A 1 550 nm long-wavelength vertical cavity surface emitting laser （VCSEL） on InP substrate is designed and fabri- cated. The transfer matrix is used to compute reflectivity spectrum of the designed epitaxial layers....A 1 550 nm long-wavelength vertical cavity surface emitting laser （VCSEL） on InP substrate is designed and fabri- cated. The transfer matrix is used to compute reflectivity spectrum of the designed epitaxial layers. The epitaxial layers mainly consist of 40 pairs of n-AlxGayIn（l-x-y）As/InP, and 6 strain compensated AlxGayln（l-x-y）As/InP quantum wells on n-InP substrate, respectively. The top distributed Bragg reflection （DBR） mirror system has been formed by fabricat- ing 4.5 pairs of SiO2/Si. The designed cavity mode is around 1 536 nm. The dip of the fabricated cavity mode is around 1 530 nm. The threshold current is 30 mA and the maximum output power is around 270 μW under CW opera- tion at room temperature.展开更多
Recent experimental breakthroughs open up new opportunities for magnetism in few-atomic-layer twodimensional(2 D) materials, which makes fabrication of new magnetic 2 D materials a fascinating issue.Here, we report th...Recent experimental breakthroughs open up new opportunities for magnetism in few-atomic-layer twodimensional(2 D) materials, which makes fabrication of new magnetic 2 D materials a fascinating issue.Here, we report the growth of monolayer VSe_2 by molecular beam epitaxy(MBE) method. Electronic properties measurements by scanning tunneling spectroscopy(STS) method revealed that the asgrown monolayer VSe_2 has magnetic characteristic peaks in its electronic density of states and a lower work-function at its edges. Moreover, air exposure experiments show air-stability of the monolayer VSe_2. This high-quality monolayer VSe_2, a very air-inert 2 D material with magnetism and low edge work function, is promising for applications in developing next-generation low power-consumption, high efficiency spintronic devices and new electrocatalysts.展开更多
High quality YBa2Cu3O6+x (YBCO) superconductive thin films have been fabricated on the SrTiO3(100) substrate using laser molecular beam epitaxy (laser-MBE).The active oxygen source was used,which made the necessary am...High quality YBa2Cu3O6+x (YBCO) superconductive thin films have been fabricated on the SrTiO3(100) substrate using laser molecular beam epitaxy (laser-MBE).The active oxygen source was used,which made the necessary ambient oxygen pressure be 2-3 orders lower than that in pulsed laser deposition (PLD).Tc0 is 85-87 K,and Jc～1.0×106 A/cm2.Atomic force microscopy (AFM) measurements show that no obvious particulates can be observed and the root mean square roughness is 7.8 nm.High stability DC superconducting quantum interference devices (DC-SQUID) was fabricated using this YBCO thin film.展开更多
基金Supported by the National Natural Science Foundation of Chin(10164003)
文摘Hydrogen-like donor impurity states in symmetric triangular quantum wells are investigated by using a variational method.Both the effects of the variable effective mass of electrons and the spatially dependent dielectric constant are considered in the calculation.The numerical results show that the binding energy depends on not only the effective mass and dielectric constant but also the spatial distribution of electron probability density.The binding energies of donor states get the maximums at the well-center.The results are also compared with those obtained in parabolic and square wells.It is seen that the triangular well support the highest binding energies for donor states.
基金Project (HKU7104/02P) supported by Research Grants Council (RGC) of Hong Kong
文摘A novel double buffer of Eu2CuO4 (ECO)/YSZ (yttrium-stabilized zirconia) was developed for growing YBa2Cu3Oy (YBCO) thin films on Si substrates. In these films, the severe reaction between Si and YBCO is blocked by the first YSZ layer, whereas, the degradation of crystallinity and superconductivity in the grown YBCO is greatly improved by the second ECO layer. Such an ECO material possesses a very stable 214-T’ structure and excellent compatibilities with YBCO and YSZ. The result shows that the epitaxy and crystallinity of YBCO deposited on Si could be considerably enhanced by using the ECO/YSZ double buffer. The grown films are characterized by high-resolution X-ray diffraction, grazing incidence X-ray reflection, and transmission electron microscopy (TEM), respectively. It is found that well defined interfaces are formed at YBCO/ECO/YSZ boundaries. No immediate layer could be seen. The defect density in all grown layers is kept at a lower level. The YBCO film surface turns out to be very smooth. These films have full superconducting transitions above 88 K and high current carrying capacity at 77 K. The successful growth of highly epitaxial YBCO thin films on silicon with ECO/YSZ buffer, demonstrate the advantages of such a double buffer structure.
文摘The growth front evolution of GaN thin films deposited on sapphire substrate by hydride vapor phase epitaxity has been studied with atomic force microscope. The evolution of the surface morphology presents four features of stage with the growth process. In initial growth stage, the surface is granular, and the typical grain diameter is about 250 nm for t =0.1 min. 3D growth plays a key role before the films come up to full coalescence, which causes a rough surface. After 0. 1 min the growth dimension decreases with the increase of lateral over growth, the surface roughness obviously decreases. From 0.4 min to 3 rain, the growth front roughness increases gradually, and the evolution of the surface roughness exhibits the characteristics of self-affined fractal. Beyond 3 min, the root-mean-square decreases gradually, which means the deposition behavior from hyper-2D growth gradually turns into layer growth mode with the increase of growth time.
文摘Photoluminescence spectra were used to characterize the boron-doped Si layers grown by molecular beam epitaxy using HBO2 as the doping source. The influence of boron doping concentration on the dislocation-related photoluminescence spectra of molecular beam epitaxy Si layers annealed at 900℃ was studied with different doping concentrations and growth temperature. The broad photoluminescence band（from 0.75eV to 0.90eV） including D1 and D2 bands was associated with high boron doping concentration in the samples, while D3 and D4 bands might be related to oxygen precipitates.
基金supported by the National Natural Science Foundation of China(Grant Nos.51372064,and 11703004)the Nature Science Foundation of Hebei Province,China(Grant Nos.E2017201227,E2017201209,and QN2017017)
文摘Transparent conducting oxides （TCOs） have attracted in- tensive attention because of their broad application in pho- toelectric devices such as solar cells, light-emitting diodes, and flat-panel displays. Current TCOs used in industry, including tin （IV） oxide （SnOz）, indium oxide （In203）, indium tin oxide （ITO）, and zinc oxide （ZnO）, are primarily n-type semiconductors [1-3]. Suitable p-type TCOs are still being researched. In the past several decades, delafossite-type compounds CuMO2 （M = Cr, A1, Ga, Fe, Sc, Y） as well as NiO, Cr203, and MoO3 have been extensively studied as potential p-type TCO candidates [4-8].
基金supported by the National High Technology and Development Program of China(No.2015AA016902)
文摘A 1 550 nm long-wavelength vertical cavity surface emitting laser （VCSEL） on InP substrate is designed and fabri- cated. The transfer matrix is used to compute reflectivity spectrum of the designed epitaxial layers. The epitaxial layers mainly consist of 40 pairs of n-AlxGayIn（l-x-y）As/InP, and 6 strain compensated AlxGayln（l-x-y）As/InP quantum wells on n-InP substrate, respectively. The top distributed Bragg reflection （DBR） mirror system has been formed by fabricat- ing 4.5 pairs of SiO2/Si. The designed cavity mode is around 1 536 nm. The dip of the fabricated cavity mode is around 1 530 nm. The threshold current is 30 mA and the maximum output power is around 270 μW under CW opera- tion at room temperature.
基金supported by the National Natural Science Foundation of China(61725107,51572290 and 11334006)National Key Research&Development Projects of China(2016YFA0202301)+1 种基金National Basic Research Program of China(2013CBA01601)Strategic Priority Research Program(B)of Chinese Academy of Sciences(XDPB06)
文摘Recent experimental breakthroughs open up new opportunities for magnetism in few-atomic-layer twodimensional(2 D) materials, which makes fabrication of new magnetic 2 D materials a fascinating issue.Here, we report the growth of monolayer VSe_2 by molecular beam epitaxy(MBE) method. Electronic properties measurements by scanning tunneling spectroscopy(STS) method revealed that the asgrown monolayer VSe_2 has magnetic characteristic peaks in its electronic density of states and a lower work-function at its edges. Moreover, air exposure experiments show air-stability of the monolayer VSe_2. This high-quality monolayer VSe_2, a very air-inert 2 D material with magnetism and low edge work function, is promising for applications in developing next-generation low power-consumption, high efficiency spintronic devices and new electrocatalysts.
基金This work was supported by the State Key Program of China (Grant No. G1998061412) the National 863 Project (Grant No. 863-CD070103) .
文摘High quality YBa2Cu3O6+x (YBCO) superconductive thin films have been fabricated on the SrTiO3(100) substrate using laser molecular beam epitaxy (laser-MBE).The active oxygen source was used,which made the necessary ambient oxygen pressure be 2-3 orders lower than that in pulsed laser deposition (PLD).Tc0 is 85-87 K,and Jc～1.0×106 A/cm2.Atomic force microscopy (AFM) measurements show that no obvious particulates can be observed and the root mean square roughness is 7.8 nm.High stability DC superconducting quantum interference devices (DC-SQUID) was fabricated using this YBCO thin film.
