An improved 4H-SiC metal-semiconductor field-effect transistors （MESFETs） with step p-buffer layer is proposed, and the static and dynamic electrical performances are analysed in this paper. A step p-buffer layer ha...An improved 4H-SiC metal-semiconductor field-effect transistors （MESFETs） with step p-buffer layer is proposed, and the static and dynamic electrical performances are analysed in this paper. A step p-buffer layer has been applied not only to increase the channel current, but also to improve the transconductance. This is due to the fact that the variation in p-buffer layer depth leads to the decrease in parasitic series resistance resulting from the change in the active channel thickness and modulation in the electric field distribution inside the channel. Detailed numerical simulations demonstrate that the saturation drain current and the maximum theoretical output power density of the proposed structure are about 30% and 37% larger than those of the conventional structure. The cut-off frequency and the maximum oscillation frequency of the proposed MESFETs are 14.5 and 62 GHz, respectively, which are higher than that of the conventional structure. Therefore, the 4H-SiC MESFETs with step p-buffer layer have superior direct-current and radio-frequency performances compared to the similar devices based on the conventional structure.展开更多
An improved structure of silicon carbide metal-semiconductor field-effect transistors （MESFET） is proposed for high power microwave applications. Numerical models for the physical and electrical mechanisms of the de...An improved structure of silicon carbide metal-semiconductor field-effect transistors （MESFET） is proposed for high power microwave applications. Numerical models for the physical and electrical mechanisms of the device are presented, and the static and dynamic electrical performances are analysed. By comparison with the conventional structure, the proposed structure exhibits a superior frequency response while possessing better DC characteristics. A p-type spacer layer, inserted between the oxide and the channel, is shown to suppress the surface trap effect and improve the distribution of the electric field at the gate edge. Meanwhile, a lightly doped n-type buffer layer under the gate reduces depletion in the channel, resulting in an increase in the output current and a reduction in the gate-capacitance. The structural parameter dependences of the device performance are discussed, and an optimized design is obtained. The results show that the maximum saturation current density of 325 mA/mm is yielded, compared with 182 mA/mm for conventional MESFETs under the condition that the breakdown voltage of the proposed MESFET is larger than that of the conventional MESFET, leading to an increase of 79% in the output power density. In addition, improvements of 27% cut-off frequency and 28% maximum oscillation frequency are achieved compared with a conventional MESFET, respectively.展开更多
Two-dimensional(2D)heterostructures based on layered transition metal dichalcogenides(TMDs)have attracted increasing attention for the applications of the nextgeneration high-performance integrated electronics and opt...Two-dimensional(2D)heterostructures based on layered transition metal dichalcogenides(TMDs)have attracted increasing attention for the applications of the nextgeneration high-performance integrated electronics and optoelectronics.Although various TMD heterostructures have been successfully fabricated,epitaxial growth of such atomically thin metal-semiconductor heterostructures with a clean and sharp interface is still challenging.In addition,photodetectors based on such heterostructures have seldom been studied.Here,we report the synthesis of high-quality vertical NbS2/MoS2metallic-semiconductor heterostructures.By using NbS2as the contact electrodes,the field-effect mobility and current on-off ratio of MoS2can be improved at least 6-fold and two orders of magnitude compared with the conventional Ti/Au contact,respectively.By using NbS2as contact,the photodetector performance of MoS2is much improved with higher responsivity and less response time.Such facile synthesis of atomically thin metal-semiconductor heterostructures by a simple chemical vapor deposition strategy and its effectiveness as ultrathin 2D metal contact open the door for the future application of electronics and optoelectronics.展开更多
The two-dimensional(2D)in-plane(lateral)heterostructures have attracted increasing interest for potential applications in the atomically thin electronics and optoelectronics.While most studies focus on semiconductorse...The two-dimensional(2D)in-plane(lateral)heterostructures have attracted increasing interest for potential applications in the atomically thin electronics and optoelectronics.While most studies focus on semiconductorsemiconductor lateral heterostructures with highly similar lattice structures between the constituent components,the synthesis of metal-semiconductor lateral heterostructures is much less explored and usually more challenging due to more distinct lattice structures or chemical properties.Herein,a vapor phase epitaxy growth method of high-quality metal-semiconductor lateral heterostructures between tetragonal CoSe and hexagonal WSe2 is reported.The 2D CoSe can selectively nucleate at the edge of pre-grown WSe2 nanosheets to form CoSe-WSe2 metal-semiconductor lateral heterostructures.Optical microscopy(OM),scanning electron microscopy(SEM),and atomic force microscopy(AFM)studies reveal distinct contrast across the heterostructure interface.High-resolution transmission electron microscopy(HRTEM)and selected area electron diffraction(SAED)studies further confirm the microstructure modulation across the heterostructure interface.The field-effect transistors(FETs)of CoSe-WSe2 lateral heterostructures show satisfactory Ohmic contacts and considerably better FET performance over those with deposited Cr/Au contacts,suggesting the in-plane metal-semiconductor junctions may function as improved contacts for the atomically thin electronics.展开更多
基金Project supported by the Fundamental Research Funds for the Central Universities(Grant No.ZYGX2009J029)
文摘An improved 4H-SiC metal-semiconductor field-effect transistors （MESFETs） with step p-buffer layer is proposed, and the static and dynamic electrical performances are analysed in this paper. A step p-buffer layer has been applied not only to increase the channel current, but also to improve the transconductance. This is due to the fact that the variation in p-buffer layer depth leads to the decrease in parasitic series resistance resulting from the change in the active channel thickness and modulation in the electric field distribution inside the channel. Detailed numerical simulations demonstrate that the saturation drain current and the maximum theoretical output power density of the proposed structure are about 30% and 37% larger than those of the conventional structure. The cut-off frequency and the maximum oscillation frequency of the proposed MESFETs are 14.5 and 62 GHz, respectively, which are higher than that of the conventional structure. Therefore, the 4H-SiC MESFETs with step p-buffer layer have superior direct-current and radio-frequency performances compared to the similar devices based on the conventional structure.
基金Project supported by the National Science Fund for Distinguished Young Scholars of China(Grant No.60725415)the National Natural Science Foundation of China(Grant No.60606006)the Pre-research Foundation of China(Grant No.51308030201)
文摘An improved structure of silicon carbide metal-semiconductor field-effect transistors （MESFET） is proposed for high power microwave applications. Numerical models for the physical and electrical mechanisms of the device are presented, and the static and dynamic electrical performances are analysed. By comparison with the conventional structure, the proposed structure exhibits a superior frequency response while possessing better DC characteristics. A p-type spacer layer, inserted between the oxide and the channel, is shown to suppress the surface trap effect and improve the distribution of the electric field at the gate edge. Meanwhile, a lightly doped n-type buffer layer under the gate reduces depletion in the channel, resulting in an increase in the output current and a reduction in the gate-capacitance. The structural parameter dependences of the device performance are discussed, and an optimized design is obtained. The results show that the maximum saturation current density of 325 mA/mm is yielded, compared with 182 mA/mm for conventional MESFETs under the condition that the breakdown voltage of the proposed MESFET is larger than that of the conventional MESFET, leading to an increase of 79% in the output power density. In addition, improvements of 27% cut-off frequency and 28% maximum oscillation frequency are achieved compared with a conventional MESFET, respectively.
基金financially supported by the National Key R&D Program of China(2018YFA0306900 and 2018YFA0305800)the National Natural Science Foundation of China(51872012)。
文摘Two-dimensional(2D)heterostructures based on layered transition metal dichalcogenides(TMDs)have attracted increasing attention for the applications of the nextgeneration high-performance integrated electronics and optoelectronics.Although various TMD heterostructures have been successfully fabricated,epitaxial growth of such atomically thin metal-semiconductor heterostructures with a clean and sharp interface is still challenging.In addition,photodetectors based on such heterostructures have seldom been studied.Here,we report the synthesis of high-quality vertical NbS2/MoS2metallic-semiconductor heterostructures.By using NbS2as the contact electrodes,the field-effect mobility and current on-off ratio of MoS2can be improved at least 6-fold and two orders of magnitude compared with the conventional Ti/Au contact,respectively.By using NbS2as contact,the photodetector performance of MoS2is much improved with higher responsivity and less response time.Such facile synthesis of atomically thin metal-semiconductor heterostructures by a simple chemical vapor deposition strategy and its effectiveness as ultrathin 2D metal contact open the door for the future application of electronics and optoelectronics.
基金the National Natural Science Foundation of China(No.51991343,No.51991340,No.61804050,No.51872086)the Fundamental Research Funds of the Central Universities(No.531107051078,No.531107051055)+1 种基金the Double First-Class Initiative of Hunan University(No.531109100004)the Hunan Key Laboratory of Two-Dimensional Materials(Grant No.2018TP1010).
文摘The two-dimensional(2D)in-plane(lateral)heterostructures have attracted increasing interest for potential applications in the atomically thin electronics and optoelectronics.While most studies focus on semiconductorsemiconductor lateral heterostructures with highly similar lattice structures between the constituent components,the synthesis of metal-semiconductor lateral heterostructures is much less explored and usually more challenging due to more distinct lattice structures or chemical properties.Herein,a vapor phase epitaxy growth method of high-quality metal-semiconductor lateral heterostructures between tetragonal CoSe and hexagonal WSe2 is reported.The 2D CoSe can selectively nucleate at the edge of pre-grown WSe2 nanosheets to form CoSe-WSe2 metal-semiconductor lateral heterostructures.Optical microscopy(OM),scanning electron microscopy(SEM),and atomic force microscopy(AFM)studies reveal distinct contrast across the heterostructure interface.High-resolution transmission electron microscopy(HRTEM)and selected area electron diffraction(SAED)studies further confirm the microstructure modulation across the heterostructure interface.The field-effect transistors(FETs)of CoSe-WSe2 lateral heterostructures show satisfactory Ohmic contacts and considerably better FET performance over those with deposited Cr/Au contacts,suggesting the in-plane metal-semiconductor junctions may function as improved contacts for the atomically thin electronics.
