A systematic investigation of the microstructure of CrA1CxN1-x coatings as a function of carbon contents was conducted. Quaternary CrA1CxN1-x coatings were deposited on Si wafers by a hybrid coating system combining a...A systematic investigation of the microstructure of CrA1CxN1-x coatings as a function of carbon contents was conducted. Quaternary CrA1CxN1-x coatings were deposited on Si wafers by a hybrid coating system combining an arc-ion plating technique and a DC reactive magnetron sputtering technique using Cr and AI targets in the Ar/N2/CH4 gaseous mixture. The effect of carbon content on microstructure of CrA1C^N~ x coatings was investigated with instrumental analyses of X-ray diffraction, X-ray photoelectron, and high-resolution transmission electron microscopy. The results show that the carbon content of CrA1CxN1-x coatings linearly increases with increasing CH4/（CH4/N2） gas flow rate ratio. The surface roughness of the CrA1CxN1-x coating layer decreases with the increase of carbon content.展开更多
Inspired by natural photosynthesis, a new series of Z-scheme Cd_xZn_(1-x)S/Au/g-C_3N_4 photocatalysts were synthesized via depositing Au particles on g-C_3N_4, followed by anchoring CdxZn_(1-x)S solid solution on the ...Inspired by natural photosynthesis, a new series of Z-scheme Cd_xZn_(1-x)S/Au/g-C_3N_4 photocatalysts were synthesized via depositing Au particles on g-C_3N_4, followed by anchoring CdxZn_(1-x)S solid solution on the pre-formed Au/g-C_3N_4 for photocatalytic hydrogen evolution. Their structure, morphology and optical property were investigated in detail. Photocatalytic activities of the developed photocatalysts for water splitting were evaluated under visible-light irradiation(k > 420 nm) using glucose as electron donor.The highest hydrogen evolution rate of 123 lmol g^(-1)h^(-1)is achieved by Cd_(0.8Z)n_(0.2)S/Au/g-C_3N_4, which is 52.2 and 8.63 times higher than that of Au/g-C_3N_4 and Cd S/Au/g-C_3N_4, respectively. The results of photoluminescence spectra, photoelectrochemical and time-resolved photoluminescence spectra indicate that the improved photocatalytic activities for Cd_xZn_(1-x)S/Au/g-C_3N_4 are due to the efficient separation of photogenerated carriers. In addition, it is noteworthy that the undesired byproducts CO and CO_2 are greatly reduced by introducing CdxZn_(1-x)S over Au/g-C_3N_4 surface. In the photocatalytic process, gluconic acid originated from the reaction of photogenerated hydroxyl radical with glucose plays a vital role on suppressing the formation of the gas byproducts. The present work will provide a new strategy to design Z-scheme photocatalysts with enhanced efficiency for water splitting along with suppressing the byproducts.展开更多
Magnetotransport properties of two-dimensional electron gases （2DEG） in AlxGa1-x N/GaN heterostructures with different Al compositions are investigated by magnetotransport measurements at low temperatures and in hig...Magnetotransport properties of two-dimensional electron gases （2DEG） in AlxGa1-x N/GaN heterostructures with different Al compositions are investigated by magnetotransport measurements at low temperatures and in high magnetic fields. It is found that heterostructures with a lower Al composition in the barrier have lower 2DEG concentration and higher 2DEG mobility.展开更多
Ternary In-rich AlxIn1-x N films were successfully grown on Si （111） and （0001） sapphire substrates by radio-frequency magnetron sputtering on a relatively Al-rich AlxIn1-x N layer after AlN buffer. X-ray diffract...Ternary In-rich AlxIn1-x N films were successfully grown on Si （111） and （0001） sapphire substrates by radio-frequency magnetron sputtering on a relatively Al-rich AlxIn1-x N layer after AlN buffer. X-ray diffraction （XRD） patterns of the films indicate highly c axis-oriented wurtzite structure and the indium content of about 0.76 has been evaluated according to the Vegard＇s law. An Al-rich AlxIn1-xN transition layer was formed between the ultimate In-rich AlxIn1-x N film and the AlN buffer, which served as a further buffer to alleviate mismatch. X-ray photoelectron spectroscopy （XPS） depth profiling analyses confirm the alternative of indium and aluminum composition and the unavoidable oxygen impurities from surface to bulk. Owing to high indium content, obvious E2u and InN-like Al （LO） phonon model accompanying with slight A1N-like A1 （LO） phonon model are observed. Hall effect measurements demonstrate n-type electrical conductivity in these alloys with carrier concentrations n=1019 cm-3. The strain in In-rich AlxIn1-x N films can be significantly reduced by introducing an Al-rich interlayer, facilitating the improvement of film quality for diverse device applications.展开更多
The influence of polarization-induced electric fields on the electron distribution and the optical properties of intersubband transitions （ISBT） in AlxGa（1-x）N/GaN coupled double quantum wells （DQWs） is investig...The influence of polarization-induced electric fields on the electron distribution and the optical properties of intersubband transitions （ISBT） in AlxGa（1-x）N/GaN coupled double quantum wells （DQWs） is investigated by self-consistent calculation. It is found that the polarization-induced potential drop leads to an asymmetric potential profile of AlxGa（1-x）N/GaN DQWs even though the two wells have the same width and depth. The polarization effects result in a very large Stark shift between the odd and even order subbands,thus shortening the wavelength of the ISBT between the first odd order and the second even order （1odd-2 ） subbands. Meanwhile, the electron distribution becomes asymmetric due to the polarization effects, and the absorption coefficient of the 1odd-2 ISBT decreases with increasing polarization field discontinuity.展开更多
The lattice dynamics of a high Al composition semiconductor alloy,Al_(0.86)Ga_(0.14)N,in comparison with intrinsic GaN and AlN are studied by Stokes/anti-Stokes Raman spectroscopy in the temperature range of 85–823 K...The lattice dynamics of a high Al composition semiconductor alloy,Al_(0.86)Ga_(0.14)N,in comparison with intrinsic GaN and AlN are studied by Stokes/anti-Stokes Raman spectroscopy in the temperature range of 85–823 K.The phonon anharmonic effect in Al_(0.86)Ga_(0.14)N is found to be stronger than that in GaN,revealing low thermal conductivity in the semiconductor alloy.Multi-phonon coupling behavior is analyzed by both Stokes Raman and anti-Stokes Raman spectroscopy.It is interesting to find that the anti-Stokes scattering exhibits stronger three-phonon coupling than the Stokes scattering,which may be due to the fact that the anti-stokes scattering process is generated from an excited state and the scattered photons have higher energies.The Stokes/anti-Stokes temperature correction factor β for Raman modes in Al_(0.86)Ga_(0.14)N alloy are all smaller than those of the corresponding intrinsic modes in GaN and AlN.The reasons for the difference in b can be attributed to three aspects,including the equipment setups,materials properties(the binding energy)and the coupling strength of Raman scattering and the sample.展开更多
The electronic band structures and band gap bowing parameters of In_xGa_（1-x）N are studied by the firstprinciples method based on the density functional theory. Calculations by employing both the Heyd-ScuseriaErnzer...The electronic band structures and band gap bowing parameters of In_xGa_（1-x）N are studied by the firstprinciples method based on the density functional theory. Calculations by employing both the Heyd-ScuseriaErnzerh of hybrid functional（HSE06） and the Perdew-Burke-Ernzerhof（PBE） one are performed. We found that the theoretical band gap bowing parameter is dependent significantly on the calculation method, especially on the exchange-correlation functional employed in the DFT calculations. The band gap of In_xGa_（1-x）N alloy decreases considerably when the In constituent x increases. It is the interactions of s–s and p–p orbitals between anions and cations that play significant roles in formatting the band gaps bowing. In general, the HSE06 hybrid functional could provide a good alternative to the PBE functional in calculating the band gap bowing parameters.展开更多
For the in-memory computation architecture,a ferroelectric semiconductor field-effect transistor(FeSFET)incorporates ferroelectric material into the FET channel to realize logic and memory in a single device.The emerg...For the in-memory computation architecture,a ferroelectric semiconductor field-effect transistor(FeSFET)incorporates ferroelectric material into the FET channel to realize logic and memory in a single device.The emerging groupⅢnitride material Al_(1-x)Sc_(x)N provides an excellent platform to explore FeSFET,as this material has significant electric polarization,ferroelectric switching,and high carrier mobility.However,steps need to be taken to reduce the large band gap of~5 eV of Al_(1-x)Sc_(x)N to improve its transport property for in-memory logic applications.By state-of-the-art first principles analysis,here we predict that alloying a relatively small amount(less than~5%)of Sb impurities into Al_(1-x)Sc_(x)N very effectively reduces the band gap while maintaining excellent ferroelectricity.We show that the co-doped Sb and Sc act cooperatively to give a significant band bowing leading to a small band gap of~1.76 eV and a large polarization parameter~0.87 C/m^(2),in the quaternary Al_(1-x)Sc_(x)Sb_(y)N_(1-y)compounds.The Sb impurity states become more continuous as a result of interactions with Sc and can be used for impurity-mediated transport.Based on the Landau-Khalatnikov model,the Landau parameters and the corresponding ferroelectric hysteresis loops are obtained for the quaternary compounds.These findings indicate that Al_(1-x)Sc_(x)Sb_(y)N_(1-y)is an excellent candidate as the channel material of FeSFET.展开更多
基金Project supported by a grant from the Fundamental R&D Program for Core Technology of Materials funded by the Ministry of Knowledge Economy, KoreaProject (2010-0001-226) supported by NCRC(National Core Research Center) Program through the National Research Foundation of Korea funded by the Ministry of Education, Science and Technology
文摘A systematic investigation of the microstructure of CrA1CxN1-x coatings as a function of carbon contents was conducted. Quaternary CrA1CxN1-x coatings were deposited on Si wafers by a hybrid coating system combining an arc-ion plating technique and a DC reactive magnetron sputtering technique using Cr and AI targets in the Ar/N2/CH4 gaseous mixture. The effect of carbon content on microstructure of CrA1C^N~ x coatings was investigated with instrumental analyses of X-ray diffraction, X-ray photoelectron, and high-resolution transmission electron microscopy. The results show that the carbon content of CrA1CxN1-x coatings linearly increases with increasing CH4/（CH4/N2） gas flow rate ratio. The surface roughness of the CrA1CxN1-x coating layer decreases with the increase of carbon content.
基金supported by the National Natural Science Foundation of China (U1403193 and 21643012)the ‘‘Western Light” Program (YB201303)the Outstanding Young Scientist Program of Chinese Academy of Sciences
文摘Inspired by natural photosynthesis, a new series of Z-scheme Cd_xZn_(1-x)S/Au/g-C_3N_4 photocatalysts were synthesized via depositing Au particles on g-C_3N_4, followed by anchoring CdxZn_(1-x)S solid solution on the pre-formed Au/g-C_3N_4 for photocatalytic hydrogen evolution. Their structure, morphology and optical property were investigated in detail. Photocatalytic activities of the developed photocatalysts for water splitting were evaluated under visible-light irradiation(k > 420 nm) using glucose as electron donor.The highest hydrogen evolution rate of 123 lmol g^(-1)h^(-1)is achieved by Cd_(0.8Z)n_(0.2)S/Au/g-C_3N_4, which is 52.2 and 8.63 times higher than that of Au/g-C_3N_4 and Cd S/Au/g-C_3N_4, respectively. The results of photoluminescence spectra, photoelectrochemical and time-resolved photoluminescence spectra indicate that the improved photocatalytic activities for Cd_xZn_(1-x)S/Au/g-C_3N_4 are due to the efficient separation of photogenerated carriers. In addition, it is noteworthy that the undesired byproducts CO and CO_2 are greatly reduced by introducing CdxZn_(1-x)S over Au/g-C_3N_4 surface. In the photocatalytic process, gluconic acid originated from the reaction of photogenerated hydroxyl radical with glucose plays a vital role on suppressing the formation of the gas byproducts. The present work will provide a new strategy to design Z-scheme photocatalysts with enhanced efficiency for water splitting along with suppressing the byproducts.
文摘Magnetotransport properties of two-dimensional electron gases （2DEG） in AlxGa1-x N/GaN heterostructures with different Al compositions are investigated by magnetotransport measurements at low temperatures and in high magnetic fields. It is found that heterostructures with a lower Al composition in the barrier have lower 2DEG concentration and higher 2DEG mobility.
基金Supported by the 863 High-Technology Research and Development Program of China(No.2009AA03Z442)the National Natural Science Foundation of China(No.61077074)the Science and Technology Department of Jilin Province(No.20090422)
文摘Ternary In-rich AlxIn1-x N films were successfully grown on Si （111） and （0001） sapphire substrates by radio-frequency magnetron sputtering on a relatively Al-rich AlxIn1-x N layer after AlN buffer. X-ray diffraction （XRD） patterns of the films indicate highly c axis-oriented wurtzite structure and the indium content of about 0.76 has been evaluated according to the Vegard＇s law. An Al-rich AlxIn1-xN transition layer was formed between the ultimate In-rich AlxIn1-x N film and the AlN buffer, which served as a further buffer to alleviate mismatch. X-ray photoelectron spectroscopy （XPS） depth profiling analyses confirm the alternative of indium and aluminum composition and the unavoidable oxygen impurities from surface to bulk. Owing to high indium content, obvious E2u and InN-like Al （LO） phonon model accompanying with slight A1N-like A1 （LO） phonon model are observed. Hall effect measurements demonstrate n-type electrical conductivity in these alloys with carrier concentrations n=1019 cm-3. The strain in In-rich AlxIn1-x N films can be significantly reduced by introducing an Al-rich interlayer, facilitating the improvement of film quality for diverse device applications.
文摘The influence of polarization-induced electric fields on the electron distribution and the optical properties of intersubband transitions （ISBT） in AlxGa（1-x）N/GaN coupled double quantum wells （DQWs） is investigated by self-consistent calculation. It is found that the polarization-induced potential drop leads to an asymmetric potential profile of AlxGa（1-x）N/GaN DQWs even though the two wells have the same width and depth. The polarization effects result in a very large Stark shift between the odd and even order subbands,thus shortening the wavelength of the ISBT between the first odd order and the second even order （1odd-2 ） subbands. Meanwhile, the electron distribution becomes asymmetric due to the polarization effects, and the absorption coefficient of the 1odd-2 ISBT decreases with increasing polarization field discontinuity.
基金supported by the National Natural Science Foundation of China(Grant No.12374013)the Fundamental Research Funds for the Central Universities(Grant No.2020SCUNL107).
文摘The lattice dynamics of a high Al composition semiconductor alloy,Al_(0.86)Ga_(0.14)N,in comparison with intrinsic GaN and AlN are studied by Stokes/anti-Stokes Raman spectroscopy in the temperature range of 85–823 K.The phonon anharmonic effect in Al_(0.86)Ga_(0.14)N is found to be stronger than that in GaN,revealing low thermal conductivity in the semiconductor alloy.Multi-phonon coupling behavior is analyzed by both Stokes Raman and anti-Stokes Raman spectroscopy.It is interesting to find that the anti-Stokes scattering exhibits stronger three-phonon coupling than the Stokes scattering,which may be due to the fact that the anti-stokes scattering process is generated from an excited state and the scattered photons have higher energies.The Stokes/anti-Stokes temperature correction factor β for Raman modes in Al_(0.86)Ga_(0.14)N alloy are all smaller than those of the corresponding intrinsic modes in GaN and AlN.The reasons for the difference in b can be attributed to three aspects,including the equipment setups,materials properties(the binding energy)and the coupling strength of Raman scattering and the sample.
基金Project supported by the National Natural Science Foundation of China(Nos.11204257,21233004)the China Postdoctoral Science Foundation(No.2012M511447)
文摘The electronic band structures and band gap bowing parameters of In_xGa_（1-x）N are studied by the firstprinciples method based on the density functional theory. Calculations by employing both the Heyd-ScuseriaErnzerh of hybrid functional（HSE06） and the Perdew-Burke-Ernzerhof（PBE） one are performed. We found that the theoretical band gap bowing parameter is dependent significantly on the calculation method, especially on the exchange-correlation functional employed in the DFT calculations. The band gap of In_xGa_（1-x）N alloy decreases considerably when the In constituent x increases. It is the interactions of s–s and p–p orbitals between anions and cations that play significant roles in formatting the band gaps bowing. In general, the HSE06 hybrid functional could provide a good alternative to the PBE functional in calculating the band gap bowing parameters.
基金supported by the National Natural Science Foundation of China(Grant No.12347101)(Shujin Guo)financial support by the National Natural Science Foundation of China(Grant No.12104313)(Xianghua Kong)+3 种基金Department of Science and Technology of Guangdong Province(Grant No.2021QN02L820)(Xianghua Kong)Shenzhen Science and Technology Program(Grant No.RCYX20231211090126026)(Xianghua Kong)Shenzhen Natural Science Fund(the Stable Support Plan Program)(Grant No.20220810161616001)(Xianghua Kong)Natural Sciences and Engineering Research Council(NSERC)of Canada(Hong Guo)。
文摘For the in-memory computation architecture,a ferroelectric semiconductor field-effect transistor(FeSFET)incorporates ferroelectric material into the FET channel to realize logic and memory in a single device.The emerging groupⅢnitride material Al_(1-x)Sc_(x)N provides an excellent platform to explore FeSFET,as this material has significant electric polarization,ferroelectric switching,and high carrier mobility.However,steps need to be taken to reduce the large band gap of~5 eV of Al_(1-x)Sc_(x)N to improve its transport property for in-memory logic applications.By state-of-the-art first principles analysis,here we predict that alloying a relatively small amount(less than~5%)of Sb impurities into Al_(1-x)Sc_(x)N very effectively reduces the band gap while maintaining excellent ferroelectricity.We show that the co-doped Sb and Sc act cooperatively to give a significant band bowing leading to a small band gap of~1.76 eV and a large polarization parameter~0.87 C/m^(2),in the quaternary Al_(1-x)Sc_(x)Sb_(y)N_(1-y)compounds.The Sb impurity states become more continuous as a result of interactions with Sc and can be used for impurity-mediated transport.Based on the Landau-Khalatnikov model,the Landau parameters and the corresponding ferroelectric hysteresis loops are obtained for the quaternary compounds.These findings indicate that Al_(1-x)Sc_(x)Sb_(y)N_(1-y)is an excellent candidate as the channel material of FeSFET.
