In this study, the physics-based device simulation tool Silvaco ATLAS is used to characterize the electrical properties of an AlGaN/GaN high electron mobility transistor （HEMT） with a U-type gate foot. The U-gate Al...In this study, the physics-based device simulation tool Silvaco ATLAS is used to characterize the electrical properties of an AlGaN/GaN high electron mobility transistor （HEMT） with a U-type gate foot. The U-gate AlGaN/GaN HEMT mainly features a gradually changed sidewall angle, which effectively mitigates the electric field in the channel, thus obtaining enhanced off-state breakdown characteristics. At the same time, only a small additional gate capacitance and decreased gate resistance ensure excellent RF characteristics for the U-gate device. U-gate AlGaN/GaN HEMTs are feasible through adjusting the etching conditions of an inductively coupled plasma system, without introducing any extra process steps. The simulation results are confirmed by experimental measurements. These features indicate that U-gate A1GaN/GaN HEMTs might be promising candidates for use in millimeter-wave power applications.展开更多
Type-II GaAsSb/InP DHBTs with selectively-etched InGaAsP ledge structures are fabricated and characterized for the first time. The novel InGaAsP/GaAsSb/InP DHBTs with a 20nm lattice-matched GaAsSb base and a 75 nm InP...Type-II GaAsSb/InP DHBTs with selectively-etched InGaAsP ledge structures are fabricated and characterized for the first time. The novel InGaAsP/GaAsSb/InP DHBTs with a 20nm lattice-matched GaAsSb base and a 75 nm InP collector have a dc current gain improvement by a factor of 2 and a cutoff frequency fT of 190 GHz. The InGaAsP ledge design provides a simple but effective approach to suppress the extrinsic base surface recombination and enable GaAsSb/InP DHBTs to further increase the operating frequencies and integration levels for millimeter wave applications.展开更多
Gate-recessed AlGaN/GaN metal-oxide-semiconductor high electron mobility transistors (MOSHEMTs) on sapphire substrates are fabricated.The devices with a gate length of 160nm and a gate periphery of 2 × 75μmexhib...Gate-recessed AlGaN/GaN metal-oxide-semiconductor high electron mobility transistors (MOSHEMTs) on sapphire substrates are fabricated.The devices with a gate length of 160nm and a gate periphery of 2 × 75μmexhibit two orders of magnitude reduction in gate leakage current and enhanced off-state breakdown characteristics,compared with conventional HEMTs.Furthermore,the extrinsic transconductance of an MOSHEMT is 237.2mS/mm,only 7% lower than that of Schottky-gate HEMT.An extrinsic current gain cutoff frequency fT of 65 GHz and a maximum oscillation frequency fmax of 123 GHz are deduced from rf small signal measurements.The high fmax demonstrates that gate-recessed MOSHEMTs are of great potential in millimeter wave frequencies.展开更多
The effect of the annealing time and annealing temperature on Ni/Ge/Au electrode contacts deposited on the n-type InP contact layer has been studied using a circular transmission line model. The minimum specific conta...The effect of the annealing time and annealing temperature on Ni/Ge/Au electrode contacts deposited on the n-type InP contact layer has been studied using a circular transmission line model. The minimum specific contact resistance of 3.210 7 cm2was achieved on the low-doped n-type InP contact layer with a 40 s anneal at 425 ℃. In order to improve the ohmic contact and reduce the difficulty in the fabrication of the high doped InP epi-layer, the doping concentration in the InP contact layer was chosen to be 51018cm 3in the fabrication of transferred electronic devices. Excellent differential negative resistance properties were obtained by an electron beam evaporating the Ni/Ge/Au/Ge/Ni/Au composite electrode on an InP epi-layer with a 60 s anneal at 380 ℃.展开更多
An ultra-high-speed, master-slave voltage comparator circuit is designed and fabricated using InP/GaInAs double heterojunction bipolar transistor technology with a current gain cutoff frequency of 170 GHz. The complet...An ultra-high-speed, master-slave voltage comparator circuit is designed and fabricated using InP/GaInAs double heterojunction bipolar transistor technology with a current gain cutoff frequency of 170 GHz. The complete chip die, including bondpads, is 0.75 × 1.04 mm22. It consumes 440 mW from a single M V power supply, excluding the clock part. 77 DHBTs have been used in the monolithic comparator. A full Nyquist test has been performed up to 20 GHz, with the input sensitivity varying from 6 mV at l0 GHz to 16 mV at 20 GHz. To our knowledge, this is the first InP based integrated circuit including more than 70 DHBTs, and it achieves the highest sampling rate found on the mainland of China.展开更多
This study reports the growth of aligned monolayer molybdenum disulfide(MoS2)ribbons on a sapphire substrate via NaOH-assisted chemical vapor deposition.The length of MoS2 ribbon is up to 400μm.The MoS2 ribbon has ex...This study reports the growth of aligned monolayer molybdenum disulfide(MoS2)ribbons on a sapphire substrate via NaOH-assisted chemical vapor deposition.The length of MoS2 ribbon is up to 400μm.The MoS2 ribbon has excellent single crystal properties,a carrier mobility of^150 cm^2V^-1s^-1,and a optical response of 103 mA W^-1 at a wavelength of 550 nm.The growth model of MoS2 ribbons was given.NaOH reacts with MoO3 to form sodium molybdate droplets,which increase the fluidity of the molybdenum source on the substrate,realizing the vapor-liquid-solid growth of MoS2 on sapphire.The monolayer MoS2 ribbons have two kinds of arrangements on the sapphire substrate,one is the oriented growth affected by the interlayer van der Waals force and the lattice,and the other is the aligned growth constrained by the sapphire step.Our results promote the basic research and device applications of MoS2,and introduce a new way of synthesizing other one dimensional(1D)and 2D nanostructures.展开更多
A large signal model for InP/InGaAs double heterojunction bipolar transistors including thermal effects has been reported,which demonstrated good agreements of simulations with measurements.On the basis of the previou...A large signal model for InP/InGaAs double heterojunction bipolar transistors including thermal effects has been reported,which demonstrated good agreements of simulations with measurements.On the basis of the previous model in which the double heterojunction effect,current blocking effect and high current effect in current expression are considered,the effect of bandgap narrowing with temperature has been considered in transport current while a formula for model parameters as a function of temperature has been developed.This model is implemented by Verilog-A and embedded in ADS.The proposed model is verified with DC and large signal measurements.展开更多
Efficient large-scale nondestructive quality assessment of graphene on Pt is essential to the in-depth growth research and practical applications of graphene.Here,we present a very simple method for directly observing...Efficient large-scale nondestructive quality assessment of graphene on Pt is essential to the in-depth growth research and practical applications of graphene.Here,we present a very simple method for directly observing the domains and defects in graphene on Pt using an ordinary optical microscope.This was achieved by modifying graphene on Pt using methylene blue(MB).Because the chemical activities of graphene and Pt surface differ significantly,the adsorption and reaction of MB on graphene and platinum surface differ.We can determine the distribution of graphene crystal domains and defects by comparing the colors in the optical images.In addition,this characterization method causes no obvious damage to the Pt substrate and graphene.Moreover,it does not affect the recycling of the substrate or the subsequent characterization or application of graphene.Our study provides a nondestructive method for measuring the quality of graphene on Pt on a large scale,as well as a reference for the characterization and doping of other two-dimensional materials.展开更多
基金Project supported by the Major Program of the National Natural Science Foundation of China （Grant No. 60890191） and the National Key Basic Research Program of China （Grant No. 2010CB327503）.
文摘In this study, the physics-based device simulation tool Silvaco ATLAS is used to characterize the electrical properties of an AlGaN/GaN high electron mobility transistor （HEMT） with a U-type gate foot. The U-gate AlGaN/GaN HEMT mainly features a gradually changed sidewall angle, which effectively mitigates the electric field in the channel, thus obtaining enhanced off-state breakdown characteristics. At the same time, only a small additional gate capacitance and decreased gate resistance ensure excellent RF characteristics for the U-gate device. U-gate AlGaN/GaN HEMTs are feasible through adjusting the etching conditions of an inductively coupled plasma system, without introducing any extra process steps. The simulation results are confirmed by experimental measurements. These features indicate that U-gate A1GaN/GaN HEMTs might be promising candidates for use in millimeter-wave power applications.
文摘Type-II GaAsSb/InP DHBTs with selectively-etched InGaAsP ledge structures are fabricated and characterized for the first time. The novel InGaAsP/GaAsSb/InP DHBTs with a 20nm lattice-matched GaAsSb base and a 75 nm InP collector have a dc current gain improvement by a factor of 2 and a cutoff frequency fT of 190 GHz. The InGaAsP ledge design provides a simple but effective approach to suppress the extrinsic base surface recombination and enable GaAsSb/InP DHBTs to further increase the operating frequencies and integration levels for millimeter wave applications.
基金Supported by Major Program of the National Natural Science Foundation of China under Grant No 60890191the National Basic Research Program of China under Grant No 2010CB327503.
文摘Gate-recessed AlGaN/GaN metal-oxide-semiconductor high electron mobility transistors (MOSHEMTs) on sapphire substrates are fabricated.The devices with a gate length of 160nm and a gate periphery of 2 × 75μmexhibit two orders of magnitude reduction in gate leakage current and enhanced off-state breakdown characteristics,compared with conventional HEMTs.Furthermore,the extrinsic transconductance of an MOSHEMT is 237.2mS/mm,only 7% lower than that of Schottky-gate HEMT.An extrinsic current gain cutoff frequency fT of 65 GHz and a maximum oscillation frequency fmax of 123 GHz are deduced from rf small signal measurements.The high fmax demonstrates that gate-recessed MOSHEMTs are of great potential in millimeter wave frequencies.
基金Project supported by the Knowledge Innovation Program of the Chinese Academy of Sciences(No.YYYJ1123)
文摘The effect of the annealing time and annealing temperature on Ni/Ge/Au electrode contacts deposited on the n-type InP contact layer has been studied using a circular transmission line model. The minimum specific contact resistance of 3.210 7 cm2was achieved on the low-doped n-type InP contact layer with a 40 s anneal at 425 ℃. In order to improve the ohmic contact and reduce the difficulty in the fabrication of the high doped InP epi-layer, the doping concentration in the InP contact layer was chosen to be 51018cm 3in the fabrication of transferred electronic devices. Excellent differential negative resistance properties were obtained by an electron beam evaporating the Ni/Ge/Au/Ge/Ni/Au composite electrode on an InP epi-layer with a 60 s anneal at 380 ℃.
文摘An ultra-high-speed, master-slave voltage comparator circuit is designed and fabricated using InP/GaInAs double heterojunction bipolar transistor technology with a current gain cutoff frequency of 170 GHz. The complete chip die, including bondpads, is 0.75 × 1.04 mm22. It consumes 440 mW from a single M V power supply, excluding the clock part. 77 DHBTs have been used in the monolithic comparator. A full Nyquist test has been performed up to 20 GHz, with the input sensitivity varying from 6 mV at l0 GHz to 16 mV at 20 GHz. To our knowledge, this is the first InP based integrated circuit including more than 70 DHBTs, and it achieves the highest sampling rate found on the mainland of China.
基金This work was financially supported by the Science and Technology Commission of Shanghai Municipality(18511110700).
文摘This study reports the growth of aligned monolayer molybdenum disulfide(MoS2)ribbons on a sapphire substrate via NaOH-assisted chemical vapor deposition.The length of MoS2 ribbon is up to 400μm.The MoS2 ribbon has excellent single crystal properties,a carrier mobility of^150 cm^2V^-1s^-1,and a optical response of 103 mA W^-1 at a wavelength of 550 nm.The growth model of MoS2 ribbons was given.NaOH reacts with MoO3 to form sodium molybdate droplets,which increase the fluidity of the molybdenum source on the substrate,realizing the vapor-liquid-solid growth of MoS2 on sapphire.The monolayer MoS2 ribbons have two kinds of arrangements on the sapphire substrate,one is the oriented growth affected by the interlayer van der Waals force and the lattice,and the other is the aligned growth constrained by the sapphire step.Our results promote the basic research and device applications of MoS2,and introduce a new way of synthesizing other one dimensional(1D)and 2D nanostructures.
基金supported by the State Key Development Program tor Basic Research of China(No.2010CB327504)
文摘A large signal model for InP/InGaAs double heterojunction bipolar transistors including thermal effects has been reported,which demonstrated good agreements of simulations with measurements.On the basis of the previous model in which the double heterojunction effect,current blocking effect and high current effect in current expression are considered,the effect of bandgap narrowing with temperature has been considered in transport current while a formula for model parameters as a function of temperature has been developed.This model is implemented by Verilog-A and embedded in ADS.The proposed model is verified with DC and large signal measurements.
基金financially supported by the National Defense Technology Innovation Special Zone Project, the National Natural Science Foundation of China (51402342)the Science and Technology Commission of Shanghai Municipality (20501130200)。
文摘Efficient large-scale nondestructive quality assessment of graphene on Pt is essential to the in-depth growth research and practical applications of graphene.Here,we present a very simple method for directly observing the domains and defects in graphene on Pt using an ordinary optical microscope.This was achieved by modifying graphene on Pt using methylene blue(MB).Because the chemical activities of graphene and Pt surface differ significantly,the adsorption and reaction of MB on graphene and platinum surface differ.We can determine the distribution of graphene crystal domains and defects by comparing the colors in the optical images.In addition,this characterization method causes no obvious damage to the Pt substrate and graphene.Moreover,it does not affect the recycling of the substrate or the subsequent characterization or application of graphene.Our study provides a nondestructive method for measuring the quality of graphene on Pt on a large scale,as well as a reference for the characterization and doping of other two-dimensional materials.
