We study the effect of the AlGaN interlayer on structural quality and strain engineering of the GaN films grown on SiC substrates with an AlN buffer layer, hnproved structural quality and tensile stress releasing are ...We study the effect of the AlGaN interlayer on structural quality and strain engineering of the GaN films grown on SiC substrates with an AlN buffer layer, hnproved structural quality and tensile stress releasing are realized in unintentionally doped GaN thin films grown on 6H-SiC substrates by metal organic chemical vapor deposition. Using the optimized AlGaN interlayer, we find that the full width at half maximum of x-ray diffraction peaks for GaN decreases dramatically, indicating an improved crystalline quality. Meanwhile, it is revealed that the biaxial tensile stress in the GaN film is significantly reduced from the Raman results. Photoluminescence spectra exhibit a shift of the peak position of the near-band-edge emission, as well as the integrated intensity ratio variation of the near-band-edge emission to the yellow luminescence band. Thus by optimizing the AlGaN interlayer, we could acquire the high-quality and strain-relaxation GaN epilayer with large thickness on SiC substrates.展开更多
We present the growth of CaN epilayer on Si （111） substrate with a single A1GaN interlayer sandwiched between the GaN epilayer and A1N buffer layer by using the metalorganic chemical vapour deposition. The influence...We present the growth of CaN epilayer on Si （111） substrate with a single A1GaN interlayer sandwiched between the GaN epilayer and A1N buffer layer by using the metalorganic chemical vapour deposition. The influence of the AlN buffer layer thickness on structural properties of the GaN epilayer has been investigated by scanning electron microscopy, atomic force microscopy, optical microscopy and high-resolution x-ray diffraction. It is found that an A1N buffer layer with the appropriate thickness plays an important role in increasing compressive strain and improving crystal quality during the growth of AlGaN interlayer, which can introduce a more compressive strain into the subsequent grown GaN layer, and reduce the crack density and threading dislocation density in GaN film.展开更多
Copper intercalated birnessite MnO_(2)(δ-MnO_(2))with weak crystallinity and high specific surface area(421 m^(2)/g)was synthesized by a one-pot redox method and investigated for low-temperature CO oxidation.The mola...Copper intercalated birnessite MnO_(2)(δ-MnO_(2))with weak crystallinity and high specific surface area(421 m^(2)/g)was synthesized by a one-pot redox method and investigated for low-temperature CO oxidation.The molar ratio of Cu/Mn was as high as 0.37,which greatly weakened the Mn-O bond and created a lot of low-temperature active oxygen species.In situ DRIFTS revealed strong bonding of copper ions with CO.As-synthesized MnO_(2)-150Cu achieved 100%conversion of 250 ppm CO in normal air(3.1 ppm H_(2)O)even at−10°C under the weight-hourly space velocity(WHSV)of 150 L/(g·h).In addition,it showed high oxygen storage capacity to oxidize CO in inert atmosphere.Though the concurrent moisture in air significantly inhibited CO adsorption and its conversion at ambient temperature,MnO_(2)-150Cu could stably convert CO in 1.3%moisture air at 70°C owing to its great low-temperature activity and reduced competitive adsorption of water with increased temperature.This study discovers the excellent low-temperature activity of weakly crystallized δ-MnO_(2) induced by high content intercalated copper ions.展开更多
AlGaN/GaN high electron mobility transistors（HEMTs）with high performance were fabricated and characterized.A variety of techniques were used to improve device performance,such as AlN interlayer,silicon nitride passi...AlGaN/GaN high electron mobility transistors（HEMTs）with high performance were fabricated and characterized.A variety of techniques were used to improve device performance,such as AlN interlayer,silicon nitride passivation,high aspect ratio T-shaped gate,low resistance ohmic contact and short drain-source distance. DC and RF performances of as-fabricated HEMTs were characterized by utilizing a semiconductor characterization system and a vector network analyzer,respectively.As-fabricated devices exhibited a maximum drain current density of 1.41 A/mm and a maximum peak extrinsic transconductance of 317 mS/mm.The obtained current density is larger than those reported in the literature to date,implemented with a domestic wafer and processes.Furthermore, a unity current gain cut-off frequency of 74.3 GHz and a maximum oscillation frequency of 112.4 GHz were obtained on a device with an 80 nm gate length.展开更多
基金Supported by the National Key R&D Program of China under Grant No 2016YFB0400200
文摘We study the effect of the AlGaN interlayer on structural quality and strain engineering of the GaN films grown on SiC substrates with an AlN buffer layer, hnproved structural quality and tensile stress releasing are realized in unintentionally doped GaN thin films grown on 6H-SiC substrates by metal organic chemical vapor deposition. Using the optimized AlGaN interlayer, we find that the full width at half maximum of x-ray diffraction peaks for GaN decreases dramatically, indicating an improved crystalline quality. Meanwhile, it is revealed that the biaxial tensile stress in the GaN film is significantly reduced from the Raman results. Photoluminescence spectra exhibit a shift of the peak position of the near-band-edge emission, as well as the integrated intensity ratio variation of the near-band-edge emission to the yellow luminescence band. Thus by optimizing the AlGaN interlayer, we could acquire the high-quality and strain-relaxation GaN epilayer with large thickness on SiC substrates.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60506001,60476021,60576003,60776047and 60836003)the National Basic Research Program of China (Grant No. 2007CB936700)the Project of Technological Research and Development of Hebei Province,China (Grant No. 07215134)
文摘We present the growth of CaN epilayer on Si （111） substrate with a single A1GaN interlayer sandwiched between the GaN epilayer and A1N buffer layer by using the metalorganic chemical vapour deposition. The influence of the AlN buffer layer thickness on structural properties of the GaN epilayer has been investigated by scanning electron microscopy, atomic force microscopy, optical microscopy and high-resolution x-ray diffraction. It is found that an A1N buffer layer with the appropriate thickness plays an important role in increasing compressive strain and improving crystal quality during the growth of AlGaN interlayer, which can introduce a more compressive strain into the subsequent grown GaN layer, and reduce the crack density and threading dislocation density in GaN film.
基金financially supported by the National Natural Science Foundation of China(No.22076094)the Science&Technology Innovation Program of Shunde of Foshan City(China)(No.2130218002526)and the Tsinghua-Foshan Innovation Special Fund(China)(No.2021THFS0503).
文摘Copper intercalated birnessite MnO_(2)(δ-MnO_(2))with weak crystallinity and high specific surface area(421 m^(2)/g)was synthesized by a one-pot redox method and investigated for low-temperature CO oxidation.The molar ratio of Cu/Mn was as high as 0.37,which greatly weakened the Mn-O bond and created a lot of low-temperature active oxygen species.In situ DRIFTS revealed strong bonding of copper ions with CO.As-synthesized MnO_(2)-150Cu achieved 100%conversion of 250 ppm CO in normal air(3.1 ppm H_(2)O)even at−10°C under the weight-hourly space velocity(WHSV)of 150 L/(g·h).In addition,it showed high oxygen storage capacity to oxidize CO in inert atmosphere.Though the concurrent moisture in air significantly inhibited CO adsorption and its conversion at ambient temperature,MnO_(2)-150Cu could stably convert CO in 1.3%moisture air at 70°C owing to its great low-temperature activity and reduced competitive adsorption of water with increased temperature.This study discovers the excellent low-temperature activity of weakly crystallized δ-MnO_(2) induced by high content intercalated copper ions.
文摘AlGaN/GaN high electron mobility transistors（HEMTs）with high performance were fabricated and characterized.A variety of techniques were used to improve device performance,such as AlN interlayer,silicon nitride passivation,high aspect ratio T-shaped gate,low resistance ohmic contact and short drain-source distance. DC and RF performances of as-fabricated HEMTs were characterized by utilizing a semiconductor characterization system and a vector network analyzer,respectively.As-fabricated devices exhibited a maximum drain current density of 1.41 A/mm and a maximum peak extrinsic transconductance of 317 mS/mm.The obtained current density is larger than those reported in the literature to date,implemented with a domestic wafer and processes.Furthermore, a unity current gain cut-off frequency of 74.3 GHz and a maximum oscillation frequency of 112.4 GHz were obtained on a device with an 80 nm gate length.
