Graphene with different surface morphologies were fabricated on 8°-off-axis and on-axis 4H-SiC(0001) substrates by high-temperature thermal decompositions. Graphene grown on Si-terminated 8°-off-axis 4H-Si...Graphene with different surface morphologies were fabricated on 8°-off-axis and on-axis 4H-SiC(0001) substrates by high-temperature thermal decompositions. Graphene grown on Si-terminated 8°-off-axis 4H-SiC(0001) shows lower Hall mobility than the counterpart of on-axis SiC substrates. The terrace width is not responsible for the different electron mobility of graphene grown on different substrates, as the terrace width is much larger than the mean free path of the electrons. The electron mobility of graphene remains unchanged with an increasing terrace width on Si- terminated on-axis SiC. Interface scattering and short-range scattering are the main factors affecting the mobility of epitaxial graphene. After the optimization of the growth process, the Hall mobility of the graphene reaches 1770 cm^2/V.s at a carrier density of 9.8.×10^12 cm^-2. Wafer-size graphene was successfully achieved with an excellent double-layer thickness uniformity of 89.7% on a 3-inch SiC substrate.展开更多
Two-dimensional electron gases(2 DEGs)formed at the interface between two oxide insulators present a promising platform for the exploration of emergent phenomena.While most of the previous works focused on SrTiO_(3-)b...Two-dimensional electron gases(2 DEGs)formed at the interface between two oxide insulators present a promising platform for the exploration of emergent phenomena.While most of the previous works focused on SrTiO_(3-)based 2 DEGs,here we took the amorphous-ABO_(3)/KTaO_(3)system as the research object to study the relationship between the interface conductivity and the redox property of B-site metal in the amorphous film.The criterion of oxide-oxide interface redox reactions for the B-site metals,Zr,Al,Ti,Ta,and Nb in conductive interfaces was revealed:the formation heat of metal oxide,ⅢH_(f)^(o),is lower than-350 kJ/(mol O)and the work function of the metalΦis in the range of 3.75 eV<Φ<4.4 eV.Furthermore,we found that the smaller absolute value ofⅢH_(f)^(o)and the larger value ofΦof the B-site metal would result in higher mobility of the two-dimensional electron gas that formed at the corresponding amorphous-ABO_(3)/KTaO_(3)interface.This finding paves the way for the design of high-mobility all-oxide electronic devices.展开更多
The temperature dependence of carrier transport properties of Alx Gal-xN/InyGal-yN/CaN and AlzGal-xN/GaN heterostructures has been investigated. It is shown that the Hall mobility in Alo.25Gao.75N/Ino.03Gao.97N/GaN he...The temperature dependence of carrier transport properties of Alx Gal-xN/InyGal-yN/CaN and AlzGal-xN/GaN heterostructures has been investigated. It is shown that the Hall mobility in Alo.25Gao.75N/Ino.03Gao.97N/GaN heterostructures is higher than that in Alo.25Gao.75N/GaN heterostructures at temperatures above 500 K, even the mobility in the former is much lower than that in the latter at 300 K. More importantly, the electron sheet density in Alo.25Gao.75N/Ino.03Gao.97N/GaN heterostructures decreases slightly, whereas the electron sheet density in Al0.25Gao.75N/CaN heterostructures gradually increases with increasing temperature above 500 K. It is believed that an electron depletion layer is formed due to the negative polarization charges at the Iny Can-yN/GaN heterointerface induced by the compressive strain in the InyCal-yN channel, which effectively suppresses the parallel conductivity originating from the thermal excitation in the underlying GaN layer at high temperatures.展开更多
Ga-doped ZnO (GZO) films are prepared on amorphous glass substrates at room temperature by radio frequency magnetron sputtering. The results reveal that the gallium doping efficiency, which will have an important in...Ga-doped ZnO (GZO) films are prepared on amorphous glass substrates at room temperature by radio frequency magnetron sputtering. The results reveal that the gallium doping efficiency, which will have an important influence on the electrical and optical properties of the film, can be governed greatly by the deposition pressure and film thickness. The position shifts of the ZnO (002) peaks in X-ray diffraction (XRD) measurements and the varied Hall mobility and carrier concentration confirms this result. The low Hall mobility is attributed to the grain boundary barrier scattering. The estimated height of barrier decreases with the increase of carrier concentration, and the trapping state density is nearly constant. According to defect formation energies and relevant chemical reactions, the photoluminescence (PL) peaks at 2.46 eV and 3.07 eV are attributed to oxygen vacancies and zinc vacancies, respectively. The substitution of more Ga atoms for Zn vacancies with the increase in film thickness is also confirmed by the PL spectrum. The obvious blueshift of the optical bandgap with an increase of carrier concentration is explained well by the Burstein Moss (BM) effect. The bandgap difference between 3.18 eV and 3.37 eV, about 0.2 eV, is attributed to the metal-semiconductor transition.展开更多
Highly conductive boron-doped hydrogenated mieroerystalline silicon (μc-Si:H) films are prepared by very high frequency plasma enhanced chemical vapour deposition (VHF PECVD) at the substrate temperatures (Ts)...Highly conductive boron-doped hydrogenated mieroerystalline silicon (μc-Si:H) films are prepared by very high frequency plasma enhanced chemical vapour deposition (VHF PECVD) at the substrate temperatures (Ts) ranging from 90℃ to 270℃. The effects of Ts on the growth and properties of the films are investigated. Results indicate that the growth rate, the electrical (dark conductivity, carrier concentration and Hall mobility) and structural (crystallinity and grain size) properties are all strongly dependent on Ts. As Ts increases, it is observed that 1) the growth rate initially increases and then arrives at a maximum value of 13.3 nm/min at Ts=210℃, 2) the crystalline volume fraction (Xc) and the grain size increase initially, then reach their maximum values at TS=140℃, and finally decrease, 3) the dark conductivity (σd), carrier concentration and Hall mobility have a similar dependence on Ts and arrive at their maximum values at Ts-190℃. In addition, it is also observed that at a lower substrate temperature Ts, a higher dopant concentration is required in order to obtain a maximum σd.展开更多
Boron-doped hydrogenated microcrystalline Germanium (lac-Ge:H) films were deposited by hot-wire CVD. H2 diluted G-ell4 and B2H6 were used as precursors and the substrate temperature was kept at 300 ℃. The properti...Boron-doped hydrogenated microcrystalline Germanium (lac-Ge:H) films were deposited by hot-wire CVD. H2 diluted G-ell4 and B2H6 were used as precursors and the substrate temperature was kept at 300 ℃. The properties of the samples were analyzed by XRD, Raman spectroscopy, Fourier transform infrared spectrometer and Hall Effect measurement with Van der Pauw method. It is found that the films are partially crystallized, with crystalline fractions larger than 45% and grain sizes smaller than 50 nm. The B-doping can enhance the crystallization but reduce the grain sizes, and also enhance the preferential growth of Ge (220). The conductivity of the films increases and tends to be saturated with increasing diborane-to-germane ratio RB2H6. All the Hall mobilities of the samples are larger than 3.8 cmZV-1·s-1. A high conductivity of展开更多
Here we report a new one-step thermal polycondensation process to form crinkly graphitic carbon nitride nanosheets(CGCNNs)via supramolecular preorganization,using a mixture of urea and melamine as the starting materia...Here we report a new one-step thermal polycondensation process to form crinkly graphitic carbon nitride nanosheets(CGCNNs)via supramolecular preorganization,using a mixture of urea and melamine as the starting material.Systematical studies reveal that the newly developed CGCNNs significantly strengthen the optical absorption,widen the bandgap,and increase the Hall mobility and carrier density compared to that of its bulk counterpart,regardless of the similar chemical composition and structure.As a result,the photocatalytic hydrogen production rate is improved by 7 times.Moreover,Na doping of CGCNNs can further promote its photocatalytic activity,leading to an excellent photocatalytic hydrogen production rate of 250.9μmol h^(–1),which is approximately 10.5 times higher than its bulk counterpart.Moreover,an impressive apparent quantum efficiency of 19.12%is achieved at 420 nm.This study provides a facile strategy for the design of efficient low-cost carbon-nitride-based photocatalysts for solar fuel production.展开更多
Indium tin oxide (ITO) films were fabricated on polyethylene terephthalate (PET) substrate at room temperature using dc magnetron sputtering technique with different sputtering powers. The structural, electrical a...Indium tin oxide (ITO) films were fabricated on polyethylene terephthalate (PET) substrate at room temperature using dc magnetron sputtering technique with different sputtering powers. The structural, electrical and optical properties were investigated by X-ray diffraction (XRD), Hall effect, reflection and transmission, respectively. XRD patterns show gradual enhancement of crystalline quality with increasing sputtering power. Significant improvement of Hall mobility due to the reduction of defects was observed though the carrier density varied slightly. Simultaneously, the mean transmission in visible light range decreased severely with increasing sputtering power. Slight move toward shorter-wavelength side of absorption peak was due to the variation of plasma wavelength. The reflection increase of near-infrared light originated from the decrease of resistivity. Finally, band gap was obtained using Tauc's relation and it was consistent with Burstein-Moss shift.展开更多
文摘Graphene with different surface morphologies were fabricated on 8°-off-axis and on-axis 4H-SiC(0001) substrates by high-temperature thermal decompositions. Graphene grown on Si-terminated 8°-off-axis 4H-SiC(0001) shows lower Hall mobility than the counterpart of on-axis SiC substrates. The terrace width is not responsible for the different electron mobility of graphene grown on different substrates, as the terrace width is much larger than the mean free path of the electrons. The electron mobility of graphene remains unchanged with an increasing terrace width on Si- terminated on-axis SiC. Interface scattering and short-range scattering are the main factors affecting the mobility of epitaxial graphene. After the optimization of the growth process, the Hall mobility of the graphene reaches 1770 cm^2/V.s at a carrier density of 9.8.×10^12 cm^-2. Wafer-size graphene was successfully achieved with an excellent double-layer thickness uniformity of 89.7% on a 3-inch SiC substrate.
基金the National Key R&D Program of China(Grant Nos.2016YFA0300701,2017YFA0206304,and 2018YFA0305704)the National Natural Science Foundation of China(Grant Nos.11934016,111921004,51972335,and 11674378)the Key Program of the Chinese Academy of Sciences(Grant Nos.XDB33030200 and QYZDY-SSW-SLH020)。
文摘Two-dimensional electron gases(2 DEGs)formed at the interface between two oxide insulators present a promising platform for the exploration of emergent phenomena.While most of the previous works focused on SrTiO_(3-)based 2 DEGs,here we took the amorphous-ABO_(3)/KTaO_(3)system as the research object to study the relationship between the interface conductivity and the redox property of B-site metal in the amorphous film.The criterion of oxide-oxide interface redox reactions for the B-site metals,Zr,Al,Ti,Ta,and Nb in conductive interfaces was revealed:the formation heat of metal oxide,ⅢH_(f)^(o),is lower than-350 kJ/(mol O)and the work function of the metalΦis in the range of 3.75 eV<Φ<4.4 eV.Furthermore,we found that the smaller absolute value ofⅢH_(f)^(o)and the larger value ofΦof the B-site metal would result in higher mobility of the two-dimensional electron gas that formed at the corresponding amorphous-ABO_(3)/KTaO_(3)interface.This finding paves the way for the design of high-mobility all-oxide electronic devices.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.60906041,60736033,60890193,and 10774001)
文摘The temperature dependence of carrier transport properties of Alx Gal-xN/InyGal-yN/CaN and AlzGal-xN/GaN heterostructures has been investigated. It is shown that the Hall mobility in Alo.25Gao.75N/Ino.03Gao.97N/GaN heterostructures is higher than that in Alo.25Gao.75N/GaN heterostructures at temperatures above 500 K, even the mobility in the former is much lower than that in the latter at 300 K. More importantly, the electron sheet density in Alo.25Gao.75N/Ino.03Gao.97N/GaN heterostructures decreases slightly, whereas the electron sheet density in Al0.25Gao.75N/CaN heterostructures gradually increases with increasing temperature above 500 K. It is believed that an electron depletion layer is formed due to the negative polarization charges at the Iny Can-yN/GaN heterointerface induced by the compressive strain in the InyCal-yN channel, which effectively suppresses the parallel conductivity originating from the thermal excitation in the underlying GaN layer at high temperatures.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 61076007 and 11174348)the National Basic Research Program of China (Grant Nos. 2009CB929404 and 2011CB302002)the Knowledge Innovation Project of the Chinese Academy of Sciences
文摘Ga-doped ZnO (GZO) films are prepared on amorphous glass substrates at room temperature by radio frequency magnetron sputtering. The results reveal that the gallium doping efficiency, which will have an important influence on the electrical and optical properties of the film, can be governed greatly by the deposition pressure and film thickness. The position shifts of the ZnO (002) peaks in X-ray diffraction (XRD) measurements and the varied Hall mobility and carrier concentration confirms this result. The low Hall mobility is attributed to the grain boundary barrier scattering. The estimated height of barrier decreases with the increase of carrier concentration, and the trapping state density is nearly constant. According to defect formation energies and relevant chemical reactions, the photoluminescence (PL) peaks at 2.46 eV and 3.07 eV are attributed to oxygen vacancies and zinc vacancies, respectively. The substitution of more Ga atoms for Zn vacancies with the increase in film thickness is also confirmed by the PL spectrum. The obvious blueshift of the optical bandgap with an increase of carrier concentration is explained well by the Burstein Moss (BM) effect. The bandgap difference between 3.18 eV and 3.37 eV, about 0.2 eV, is attributed to the metal-semiconductor transition.
文摘Highly conductive boron-doped hydrogenated mieroerystalline silicon (μc-Si:H) films are prepared by very high frequency plasma enhanced chemical vapour deposition (VHF PECVD) at the substrate temperatures (Ts) ranging from 90℃ to 270℃. The effects of Ts on the growth and properties of the films are investigated. Results indicate that the growth rate, the electrical (dark conductivity, carrier concentration and Hall mobility) and structural (crystallinity and grain size) properties are all strongly dependent on Ts. As Ts increases, it is observed that 1) the growth rate initially increases and then arrives at a maximum value of 13.3 nm/min at Ts=210℃, 2) the crystalline volume fraction (Xc) and the grain size increase initially, then reach their maximum values at TS=140℃, and finally decrease, 3) the dark conductivity (σd), carrier concentration and Hall mobility have a similar dependence on Ts and arrive at their maximum values at Ts-190℃. In addition, it is also observed that at a lower substrate temperature Ts, a higher dopant concentration is required in order to obtain a maximum σd.
基金Funded by the National High-tech Research and Development Program of China(863 Program)(No.2006AA03Z219)Graduate Innovation Plan of Nanjing University of Aeronautics and Astronautics(No.BCXJ08-10)the National Natural Science Foundation of China(No.61306084)
文摘Boron-doped hydrogenated microcrystalline Germanium (lac-Ge:H) films were deposited by hot-wire CVD. H2 diluted G-ell4 and B2H6 were used as precursors and the substrate temperature was kept at 300 ℃. The properties of the samples were analyzed by XRD, Raman spectroscopy, Fourier transform infrared spectrometer and Hall Effect measurement with Van der Pauw method. It is found that the films are partially crystallized, with crystalline fractions larger than 45% and grain sizes smaller than 50 nm. The B-doping can enhance the crystallization but reduce the grain sizes, and also enhance the preferential growth of Ge (220). The conductivity of the films increases and tends to be saturated with increasing diborane-to-germane ratio RB2H6. All the Hall mobilities of the samples are larger than 3.8 cmZV-1·s-1. A high conductivity of
基金financial support from the National Natural Science Foundation of China(No.52002328)the Fundamental Research Funds for the Central Universities+1 种基金the Joint Research Funds of Department of Science&Technology of Shaanxi Province and Northwestern Polytechnical University(2020GXLH-Z018)the Australian Research Council through its Discovery Projects(DPs)and Laureate Fellowship。
文摘Here we report a new one-step thermal polycondensation process to form crinkly graphitic carbon nitride nanosheets(CGCNNs)via supramolecular preorganization,using a mixture of urea and melamine as the starting material.Systematical studies reveal that the newly developed CGCNNs significantly strengthen the optical absorption,widen the bandgap,and increase the Hall mobility and carrier density compared to that of its bulk counterpart,regardless of the similar chemical composition and structure.As a result,the photocatalytic hydrogen production rate is improved by 7 times.Moreover,Na doping of CGCNNs can further promote its photocatalytic activity,leading to an excellent photocatalytic hydrogen production rate of 250.9μmol h^(–1),which is approximately 10.5 times higher than its bulk counterpart.Moreover,an impressive apparent quantum efficiency of 19.12%is achieved at 420 nm.This study provides a facile strategy for the design of efficient low-cost carbon-nitride-based photocatalysts for solar fuel production.
基金supported by the National Natural Science Foundation of China (No. 51071038)Program forNew Century Excellent Talents in University (NCET-09-0265)+1 种基金Sichuan Province Science Foundation for Youths(No. 2010JQ0002)State Key Laboratory for Mechanical Behavior of Materials, Xi an Jiaotong University(No. 201011005)
文摘Indium tin oxide (ITO) films were fabricated on polyethylene terephthalate (PET) substrate at room temperature using dc magnetron sputtering technique with different sputtering powers. The structural, electrical and optical properties were investigated by X-ray diffraction (XRD), Hall effect, reflection and transmission, respectively. XRD patterns show gradual enhancement of crystalline quality with increasing sputtering power. Significant improvement of Hall mobility due to the reduction of defects was observed though the carrier density varied slightly. Simultaneously, the mean transmission in visible light range decreased severely with increasing sputtering power. Slight move toward shorter-wavelength side of absorption peak was due to the variation of plasma wavelength. The reflection increase of near-infrared light originated from the decrease of resistivity. Finally, band gap was obtained using Tauc's relation and it was consistent with Burstein-Moss shift.