We report molecular beam epitaxial growth and electrical and ultraviolet light emitting properties of(AlN)m/(GaN)n superlattices(SLs),where m and n represent the numbers of monolayers.Clear satellite peaks observed in...We report molecular beam epitaxial growth and electrical and ultraviolet light emitting properties of(AlN)m/(GaN)n superlattices(SLs),where m and n represent the numbers of monolayers.Clear satellite peaks observed in XRD 2θ-ωscans and TEM images evidence the formation of clear periodicity and atomically sharp interfaces.For(AlN)m/(GaN)n SLs with an average Al composition of 50%,we have obtained an electron density up to 4.48×10^(19)cm^(-3)and a resistivity of 0.002Ω·cm,and a hole density of 1.83×10^(18)cm^(-3)with a resistivity of 3.722Ω·cm,both at room temperature.Furthermore,the(AlN)m/(GaN)n SLs exhibit a blue shift for their photoluminescence peaks,from 403 nm to 318 nm as GaN is reduced from n=11 to n=4 MLs,reaching the challenging UVB wavelength range.The results demonstrate that the(AlN)m/(GaN)n SLs have the potential to enhance the conductivity and avoid the usual random alloy scattering of the high-Al-composition ternary AlGaN,making them promising functional components in both UVB emitter and AlGaN channel high electron mobility transistor applications.展开更多
A systematic investigation on PA-MBE grown GaN with low growth rates(less than 0.2μm/h)has been conducted in a wide growth temperature range,in order to guide future growth of sophisticated fine structures for quantu...A systematic investigation on PA-MBE grown GaN with low growth rates(less than 0.2μm/h)has been conducted in a wide growth temperature range,in order to guide future growth of sophisticated fine structures for quantum device applications.Similar to usual growths with higher growth rates,three growth regions have been revealed,namely,Ga droplets,slightly Ga-rich and N-rich 3D growth regions.The slightly Ga-rich region is preferred,in which GaN epilayers demonstrate optimal crystalline quality,which has been demonstrated by streaky RHEED patterns,atomic smooth surface morphology,and very low defect related yellow and blue luminescence bands.The growth temperature is a critical parameter to obtain high quality materials and the optimal growth temperature window(~700-760℃)has been identified.The growth rate shows a strong dependence on growth temperatures in the optimal temperature window,and attention must be paid when growing fine structures at a low growth rate.Mg and Si doped GaN were also studied,and both p-and n-type materials were obtained.展开更多
A series of In Sb thin films were grown on Ga As substrates by molecular beam epitaxy(MBE).Ga Sb/Al In Sb is used as a compound buffer layer to release the strain caused by the lattice mismatch between the substrate a...A series of In Sb thin films were grown on Ga As substrates by molecular beam epitaxy(MBE).Ga Sb/Al In Sb is used as a compound buffer layer to release the strain caused by the lattice mismatch between the substrate and the epitaxial layer,so as to reduce the system defects.At the same time,the influence of different interface structures of Al In Sb on the surface morphology of buffer layer is explored.The propagation mechanism of defects with the growth of buffer layer is compared and analyzed.The relationship between the quality of In Sb thin films and the structure of buffer layer is summarized.Finally,the growth of high quality In Sb thin films is realized.展开更多
Atomically thin transition metal dichalcogenide films with distorted trigonal(1T') phase have been predicted to be candidates for realizing quantum spin Hall effect. Growth of 1T' film and experimental investi...Atomically thin transition metal dichalcogenide films with distorted trigonal(1T') phase have been predicted to be candidates for realizing quantum spin Hall effect. Growth of 1T' film and experimental investigation of its electronic structure are critical. Here we report the electronic structure of 1T'-MoTe2 films grown by molecular beam epitaxy(MBE).Growth of the 1T'-MoTe2 film depends critically on the substrate temperature, and successful growth of the film is indicated by streaky stripes in the reflection high energy electron diffraction(RHEED) and sharp diffraction spots in the low energy electron diffraction(LEED). Angle-resolved photoemission spectroscopy(ARPES) measurements reveal a metallic behavior in the as-grown film with an overlap between the conduction and valence bands. First principles calculation suggests that a suitable tensile strain along the a-axis direction is needed to induce a gap to make it an insulator. Our work not only reports the electronic structure of MBE grown 1T'-MoTe2 films, but also provides insights for strain engineering to make it possible for quantum spin Hall effect.展开更多
We perform molecular beam epitaxy growth and scanning tunneling microscopy study of copper diselenide （CuSe2 ） films on SrTiO3 （001）. Using a Se-rich condition, the single-phase pyrite CuSe2 grows in the Stranski-...We perform molecular beam epitaxy growth and scanning tunneling microscopy study of copper diselenide （CuSe2 ） films on SrTiO3 （001）. Using a Se-rich condition, the single-phase pyrite CuSe2 grows in the Stranski-Krastanov （layer-plus-island） mode with a preferential orientation of （111）. Our careful inspection of both the as-grown and post-annealed CuSe2 films at various temperatures invariably shows a Cu-terminated surface, which, depending on the annealing temperature, reconstructs into two distinct structures 2 ×√3 and √x ×√3-R30°. The Cu termi- nation is supported by the depressed density of states near the Fermi level, measured by in-situ low temperature scanning tunneling spectroscopy. Our study helps understand the preparation and surface chemistry of transition metal pyrite dichalcogenides thin films.展开更多
基金Project supported by the National Key R&D Program of China(Grant No.2022YFB3605600)the National Natural Science Foundation of China(Grant No.61974065)+3 种基金the Key R&D Project of Jiangsu Province,China(Grant Nos.BE2020004-3 and BE2021026)Postdoctoral Fellowship Program of CPSF(Grant No.GZC20231098)the Jiangsu Special ProfessorshipCollaborative Innovation Center of Solid State Lighting and Energy-saving Electronics。
文摘We report molecular beam epitaxial growth and electrical and ultraviolet light emitting properties of(AlN)m/(GaN)n superlattices(SLs),where m and n represent the numbers of monolayers.Clear satellite peaks observed in XRD 2θ-ωscans and TEM images evidence the formation of clear periodicity and atomically sharp interfaces.For(AlN)m/(GaN)n SLs with an average Al composition of 50%,we have obtained an electron density up to 4.48×10^(19)cm^(-3)and a resistivity of 0.002Ω·cm,and a hole density of 1.83×10^(18)cm^(-3)with a resistivity of 3.722Ω·cm,both at room temperature.Furthermore,the(AlN)m/(GaN)n SLs exhibit a blue shift for their photoluminescence peaks,from 403 nm to 318 nm as GaN is reduced from n=11 to n=4 MLs,reaching the challenging UVB wavelength range.The results demonstrate that the(AlN)m/(GaN)n SLs have the potential to enhance the conductivity and avoid the usual random alloy scattering of the high-Al-composition ternary AlGaN,making them promising functional components in both UVB emitter and AlGaN channel high electron mobility transistor applications.
基金the National Natural Science Foundation of China(Grant Nos.62074077,61921005,61974062,and 61974065)the Fundamental Research Funds for the Central Universities,China(Grant No.14380166)+3 种基金Key R&D Program of Jiangsu Province,China(Grant No.BE2020004-3)the National Key R&D Program of China(Grant No.2017YFB0404101)Nature Science Foundation of Jiangsu Province,China(Grant No.BE2015111)Collaborative Innovation Center of Solid State Lighting and Energysaving Electronics.
文摘A systematic investigation on PA-MBE grown GaN with low growth rates(less than 0.2μm/h)has been conducted in a wide growth temperature range,in order to guide future growth of sophisticated fine structures for quantum device applications.Similar to usual growths with higher growth rates,three growth regions have been revealed,namely,Ga droplets,slightly Ga-rich and N-rich 3D growth regions.The slightly Ga-rich region is preferred,in which GaN epilayers demonstrate optimal crystalline quality,which has been demonstrated by streaky RHEED patterns,atomic smooth surface morphology,and very low defect related yellow and blue luminescence bands.The growth temperature is a critical parameter to obtain high quality materials and the optimal growth temperature window(~700-760℃)has been identified.The growth rate shows a strong dependence on growth temperatures in the optimal temperature window,and attention must be paid when growing fine structures at a low growth rate.Mg and Si doped GaN were also studied,and both p-and n-type materials were obtained.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61774130,11474248,61790581,and 51973070)the Ph.D.Program Foundation of the Ministry of Education of China(Grant No.20105303120002)the National Key Technology Research and Development Program of China(Grant No.2018YFA0209101)。
文摘A series of In Sb thin films were grown on Ga As substrates by molecular beam epitaxy(MBE).Ga Sb/Al In Sb is used as a compound buffer layer to release the strain caused by the lattice mismatch between the substrate and the epitaxial layer,so as to reduce the system defects.At the same time,the influence of different interface structures of Al In Sb on the surface morphology of buffer layer is explored.The propagation mechanism of defects with the growth of buffer layer is compared and analyzed.The relationship between the quality of In Sb thin films and the structure of buffer layer is summarized.Finally,the growth of high quality In Sb thin films is realized.
基金Project supported by the National Basic Research Program of China(Grant Nos.2016YFA0301004 and 2015CB921001)the National Natural Science Foundation of China(Grant Nos.11334006,11725418,and 11674188)
文摘Atomically thin transition metal dichalcogenide films with distorted trigonal(1T') phase have been predicted to be candidates for realizing quantum spin Hall effect. Growth of 1T' film and experimental investigation of its electronic structure are critical. Here we report the electronic structure of 1T'-MoTe2 films grown by molecular beam epitaxy(MBE).Growth of the 1T'-MoTe2 film depends critically on the substrate temperature, and successful growth of the film is indicated by streaky stripes in the reflection high energy electron diffraction(RHEED) and sharp diffraction spots in the low energy electron diffraction(LEED). Angle-resolved photoemission spectroscopy(ARPES) measurements reveal a metallic behavior in the as-grown film with an overlap between the conduction and valence bands. First principles calculation suggests that a suitable tensile strain along the a-axis direction is needed to induce a gap to make it an insulator. Our work not only reports the electronic structure of MBE grown 1T'-MoTe2 films, but also provides insights for strain engineering to make it possible for quantum spin Hall effect.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11374336 and 61176078
文摘We perform molecular beam epitaxy growth and scanning tunneling microscopy study of copper diselenide （CuSe2 ） films on SrTiO3 （001）. Using a Se-rich condition, the single-phase pyrite CuSe2 grows in the Stranski-Krastanov （layer-plus-island） mode with a preferential orientation of （111）. Our careful inspection of both the as-grown and post-annealed CuSe2 films at various temperatures invariably shows a Cu-terminated surface, which, depending on the annealing temperature, reconstructs into two distinct structures 2 ×√3 and √x ×√3-R30°. The Cu termi- nation is supported by the depressed density of states near the Fermi level, measured by in-situ low temperature scanning tunneling spectroscopy. Our study helps understand the preparation and surface chemistry of transition metal pyrite dichalcogenides thin films.
