GaN-based p-channel heterostructure field-effect transistors(p-HFETs)face significant constraints on on-state currents compared with n-channel high electron mobility transistors.In this work,we propose a novel double ...GaN-based p-channel heterostructure field-effect transistors(p-HFETs)face significant constraints on on-state currents compared with n-channel high electron mobility transistors.In this work,we propose a novel double heterostructure which introduces an additional p-GaN insertion layer into traditional p-HFETs.The impact of the device structure on the hole densities and valence band energies of both the upper and lower channels is analyzed by using Silvaco TACD simulations,including the thickness of the upper AlGaN layer and the doping impurities and concentration in the GaN buffer layer,as well as the thickness and Mg-doping concentration in the p-GaN insertion layer.With the help of the p-GaN insertion layer,the C-doping concentration in the GaN buffer layer can be reduced,while the density of the two-dimensional hole gas in the lower channel is enhanced at the same time.This work suggests that a double heterostructure with a p-GaN insertion layer is a better approach to improve p-HFETs compared with those devices with C-doped buffer layer alone.展开更多
Black phosphorous(BP),an excellent two-dimensional(2D)monoelemental layered p-type semiconductor material with high carrier mobility and thickness-dependent tunable direct bandgap structure,has been widely applied in ...Black phosphorous(BP),an excellent two-dimensional(2D)monoelemental layered p-type semiconductor material with high carrier mobility and thickness-dependent tunable direct bandgap structure,has been widely applied in various devices.As the essential building blocks for modern electronic and optoelectronic devices,high quality PN junctions based on semiconductors have attracted widespread attention.Herein,we report a junction field-effect transistor(JFET)by integrating narrow-gap p-type BP and ultra-wide gap n-typeβ-Ga2O3 nanoflakes for the first time.BP andβ-Ga2O3 form a vertical van der Waals(vdW)heterostructure by mechanically exfoliated method.The BP/β-Ga2O3 vdW heterostructure exhibits remarkable PN diode rectifying characteristics with a high rectifying ratio about 107 and a low reverse current around pA.More interestingly,by using the BP as the gate andβ-Ga2O3 as the channel,the BP/β-Ga2O3 JFET devices demonstrate excellent n-channel JFET characteristics with the on/off ratio as high as 107,gate leakage current around as low as pA,maximum transconductance(gm)up to 25.3μS and saturation drain current(IDSS)of 16.5μA/μm.Moreover,it has a pinch-off voltage of–20 V and a minimum subthreshold swing of 260 mV/dec.These excellent n-channel JFET characteristics will expand the application of BP in future nanoelectronic devices.展开更多
In this paper, TiN/A1Ox gated A1GaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOS- HFETs) were fabricated for gate-first process evaluation. By employing a low temperature ohmic process...In this paper, TiN/A1Ox gated A1GaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOS- HFETs) were fabricated for gate-first process evaluation. By employing a low temperature ohmic process, ohmic contact can be obtained by annealing at 600 ℃ with the contact resistance approximately 1.6 Ω.mm. The ohmic annealing process also acts as a post-deposition annealing on the oxide film, resulting in good device performance. Those results demonstrated that the TiN/A1Ox gated MOS-HFETs with low temperature ohmic process can be applied for self-aligned gate AIGaN/GaN MOS-HFETs.展开更多
We simulate the current-voltage (I-V) characteristics of AlGaN/AlN/GaN heterostructure field-effect transistors (HFETs) with different gate lengths using the quasi-two-dimensional (quasi-2D) model. The calculati...We simulate the current-voltage (I-V) characteristics of AlGaN/AlN/GaN heterostructure field-effect transistors (HFETs) with different gate lengths using the quasi-two-dimensional (quasi-2D) model. The calculation results obtained using the modified mobility model are found to accord well with the experimental data. By analyzing the variation of the electron mobility for the two-dimensional electron gas (213EG) with the electric field in the linear region of the AlGaN/AlN/GaN HFET I-V output characteristics, it is found that the polarization Coulomb field scattering still plays an important role in the electron mobility of AlGaN/AlN/GaN HFETs at the higher drain voltage and channel electric field. As drain voltage and channel electric field increase, the 2DEG density reduces and the polarization Coulomb field scattering increases, as a result, the 2DEG electron mobility decreases.展开更多
The parasitic source resistance(RS) of AlGaN/AlN/GaN heterostructure field-effect transistors(HFETs) is studied in the temperature range 300–500 K. By using the measured RSand both capacitance–voltage(C–V) an...The parasitic source resistance(RS) of AlGaN/AlN/GaN heterostructure field-effect transistors(HFETs) is studied in the temperature range 300–500 K. By using the measured RSand both capacitance–voltage(C–V) and current–voltage(I–V) characteristics for the fabricated device at 300, 350, 400, 450, and 500 K, it is found that the polarization Coulomb field(PCF) scattering exhibits a significant impact on RSat the above-mentioned different temperatures. Furthermore, in the AlGaN/AlN/GaN HFETs, the interaction between the additional positive polarization charges underneath the gate contact and the additional negative polarization charges near the source Ohmic contact, which is related to the PCF scattering, is verified during the variable-temperature study of RS.展开更多
By making use of the quasi-two-dimensional (quasi-2D) model, the current-voltage (l-V) characteristics of In0AsA10.82N/A1N/GaN heterostructure field-effect transistors (HFETs) with different gate lengths are sim...By making use of the quasi-two-dimensional (quasi-2D) model, the current-voltage (l-V) characteristics of In0AsA10.82N/A1N/GaN heterostructure field-effect transistors (HFETs) with different gate lengths are simulated based on the measured capacitance-voltage (C-V) characteristics and I-V characteristics. By analyzing the variation of the electron mobility for the two-dimensional electron gas (2DEG) with electric field, it is found that the different polarization charge distributions generated by the different channel electric field distributions can result in different polarization Coulomb field scatterings. The difference between the electron mobilities primarily caused by the polarization Coulomb field scatterings can reach up to 1522.9 cm2/V.s for the prepared In0.38AI0.82N/A1N/GaN HFETs. In addition, when the 2DEG sheet density is modulated by the drain-source bias, the electron mobility presents a peak with the variation of the 2DEG sheet density, the gate length is smaller, and the 2DEG sheet density corresponding to the peak point is higher.展开更多
We report a novel structure of A1GaN/GaN heterostructure field effect transistors (HFETs) with a Si and Mg pair- doped interlayer grown on Si substrate. By optimizing the doping concentrations of the pair-doped inte...We report a novel structure of A1GaN/GaN heterostructure field effect transistors (HFETs) with a Si and Mg pair- doped interlayer grown on Si substrate. By optimizing the doping concentrations of the pair-doped interlayers, the mobility of 2DEG increases by twice for the conventional structure under 5 K due to the improved crystalline quality of the conduction channel. The proposed HFET shows a four orders lower off-state leakage current, resulting in a much higher on/off ratio ( - 10^9). Further temperature-dependent performance of Schottky diodes revealed that the inhibition of shallow surface traps in proposed HFETs should be the main reason for the suppression of leakage current.展开更多
A simple and effective approach to improve the switching characteristics of AlGaN/AlN/GaN heterostructure field effect transistors (HFETs) by applying a voltage bias on the substrate is presented. With the increase ...A simple and effective approach to improve the switching characteristics of AlGaN/AlN/GaN heterostructure field effect transistors (HFETs) by applying a voltage bias on the substrate is presented. With the increase of the substrate bias, the OFF-state drain current is much reduced and the ON-state current keeps constant. Both the ON/OFF current ratio and the subthreshold swing are demonstrated to be greatly improved. With the thinned substrate, the improvement of the switching characteristics with the substrate bias is found to be even greater. The above improvements of the switching characteristics are attributed to the interaction between the substrate bias induced electrical field and the bulk traps in the GaN buffer layer, which reduces the conductivity of the GaN buffer layer.展开更多
Two-dimensional(2D) materials have attracted extensive interest due to their excellent electrical, thermal,mechanical, and optical properties. Graphene has been one of the most explored 2D materials. However, its zero...Two-dimensional(2D) materials have attracted extensive interest due to their excellent electrical, thermal,mechanical, and optical properties. Graphene has been one of the most explored 2D materials. However, its zero band gap has limited its applications in electronic devices. Transition metal dichalcogenide(TMDC), another kind of 2D material,has a nonzero direct band gap(same charge carrier momentum in valence and conduction band) at monolayer state,promising for the efficient switching devices(e.g., field-effect transistors). This review mainly focuses on the recent advances in charge carrier mobility and the challenges to achieve high mobility in the electronic devices based on 2DTMDC materials and also includes an introduction of 2D materials along with the synthesis techniques. Finally, this review describes the possible methodology and future prospective to enhance the charge carrier mobility for electronic devices.展开更多
In this paper, we present a monolithic integration of a self-protected AlGaN/GaN metal-insulator field-effect transistor (MISFET). An integrated field-controlled diode on the drain side of the AlGaN/GaN MISFET featu...In this paper, we present a monolithic integration of a self-protected AlGaN/GaN metal-insulator field-effect transistor (MISFET). An integrated field-controlled diode on the drain side of the AlGaN/GaN MISFET features a self- protected function for a reverse bias. This diode takes advantage of the recessed-barrier enhancement-mode technique to realize an ultra-low voltage drop and a low turn-ON voltage. In the smart monolithic integration, this integrated diode can block a reverse bias (〉 70 V/μm) and suppress the leakage current (〈 5 × 10-11 A/mm). Compared with conventional monolithic integration, the numerical results show that the MISET integrated with a field-controlled diode leads to a good performance for smart power integration. And the power loss is lower than 50% in conduction without forward current degeneration.展开更多
Layered semiconductor heterostructures are essential elements in modern electronic and optoelectronic devices.Dynamically engineering the composition of these heterostructures may enable the flexible design of the pro...Layered semiconductor heterostructures are essential elements in modern electronic and optoelectronic devices.Dynamically engineering the composition of these heterostructures may enable the flexible design of the properties of heterostructure-based electronics and optoelectronics as well as their optimization.Here,we report for the first time a two-step chemical vapor deposition approach for a series of WS2(1−x)Se2x/SnS2 vertical heterostructures with high-quality and large areas.The steady-state photoluminescence results exhibit an obvious composition-related quenching ratio,revealing a strong coherence between the band offset and the charge transfer efficiency at the junction interface.Based on the achieved heterostructures,dual-channel backgate field-effect transistors were successfully designed and exhibited typical composition-dependent transport behaviors,and pure n-type unipolar transistors to ambipolar transistors were realized in such systems.The direct vapor growth of these novel vertical WS2(1−x)Se2x/SnS2 heterostructures could offer an interesting system for probing new physical properties and provide a series of layered heterostructures for high-quality devices.展开更多
Based on the measured capacitance–voltage(C–V) curves and current–voltage(I–V) curves for the prepared differently-sized AlN/GaN heterostructure field-effect transistors(HFETs), the I–V characteristics of t...Based on the measured capacitance–voltage(C–V) curves and current–voltage(I–V) curves for the prepared differently-sized AlN/GaN heterostructure field-effect transistors(HFETs), the I–V characteristics of the AlN/GaN HFETs were simulated using the quasi-two-dimensional(quasi-2D) model. By analyzing the variation in the electron mobility for the two-dimensional electron gas(2DEG) with the channel electric field, it is found that the different polarization charge distribution generated by the different channel electric field distribution can result in different polarization Coulomb field(PCF) scattering. The 2DEG electron mobility difference is mostly caused by the PCF scattering which can reach up to 899.6 cm^2/(V·s)(sample a), 1307.4 cm^2/(V·s)(sample b),1561.7 cm^2/(V s)(sample c) and 678.1 cm^2/(V·s)(sample d), respectively. When the 2DEG sheet density is modulated by the drain–source bias, the electron mobility for samples a, b and c appear to peak with the variation of the 2DEG sheet density, but for sample d, no peak appears and the electron mobility rises with the increase in the2 DEG sheet density.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
Low-symmetry two-dimensional(2D)materials,with unique in-plane direction-dependent optical,electrical,and thermoelectric properties,have been intensively studied for their potential application values in advanced elec...Low-symmetry two-dimensional(2D)materials,with unique in-plane direction-dependent optical,electrical,and thermoelectric properties,have been intensively studied for their potential application values in advanced electronic and optoelectronic devices.However,since anisotropic 2D materials are highly sensitive to the environmental factors,researches on their high-performance field-effect transistors(FETs)are still limited.Here,we report a high-performance SnSe FET based on a van der Waals(vdWs)heterostructure of SnSe encapsulated in hexagonal boron nitride(/7BN)together with graphene contacts.The device exhibits a high on/off ratio exceeding 1 × 10^(9),and a carrier mobility of 118 cm^(2)·V^(-1)s^(-1).Our work highlights low-symmetry 2D SnSe holds potential to be used for designing excellent electronic devices.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.62104184,62234009,62090014,62188102,62104178,and 62104179)the Fundamental Research Funds for the Central Universities of China(Grant Nos.YJSJ23019,XJSJ23047,and ZDRC2002)+1 种基金the China National Postdoctoral Program for Innovative Talents(Grant No.BX20200262)the China Postdoctoral Science Foundation(Grant No.2021M692499)。
文摘GaN-based p-channel heterostructure field-effect transistors(p-HFETs)face significant constraints on on-state currents compared with n-channel high electron mobility transistors.In this work,we propose a novel double heterostructure which introduces an additional p-GaN insertion layer into traditional p-HFETs.The impact of the device structure on the hole densities and valence band energies of both the upper and lower channels is analyzed by using Silvaco TACD simulations,including the thickness of the upper AlGaN layer and the doping impurities and concentration in the GaN buffer layer,as well as the thickness and Mg-doping concentration in the p-GaN insertion layer.With the help of the p-GaN insertion layer,the C-doping concentration in the GaN buffer layer can be reduced,while the density of the two-dimensional hole gas in the lower channel is enhanced at the same time.This work suggests that a double heterostructure with a p-GaN insertion layer is a better approach to improve p-HFETs compared with those devices with C-doped buffer layer alone.
基金supported by the National Natural Science Foundation of China(Grant No.61922082,61875223,61927813)the Natural Science Foundation of Jiangsu Province(Grant No.BK20191195)The support from the Vacuum Interconnected Nanotech Workstation(Nano-X)of Suzhou Institute of Nano-tech and Nano-bionics(SINANO),Chinese Academy of Sciences。
文摘Black phosphorous(BP),an excellent two-dimensional(2D)monoelemental layered p-type semiconductor material with high carrier mobility and thickness-dependent tunable direct bandgap structure,has been widely applied in various devices.As the essential building blocks for modern electronic and optoelectronic devices,high quality PN junctions based on semiconductors have attracted widespread attention.Herein,we report a junction field-effect transistor(JFET)by integrating narrow-gap p-type BP and ultra-wide gap n-typeβ-Ga2O3 nanoflakes for the first time.BP andβ-Ga2O3 form a vertical van der Waals(vdW)heterostructure by mechanically exfoliated method.The BP/β-Ga2O3 vdW heterostructure exhibits remarkable PN diode rectifying characteristics with a high rectifying ratio about 107 and a low reverse current around pA.More interestingly,by using the BP as the gate andβ-Ga2O3 as the channel,the BP/β-Ga2O3 JFET devices demonstrate excellent n-channel JFET characteristics with the on/off ratio as high as 107,gate leakage current around as low as pA,maximum transconductance(gm)up to 25.3μS and saturation drain current(IDSS)of 16.5μA/μm.Moreover,it has a pinch-off voltage of–20 V and a minimum subthreshold swing of 260 mV/dec.These excellent n-channel JFET characteristics will expand the application of BP in future nanoelectronic devices.
基金Project supported by the International Science and Technology Collaboration Program of China(Grant No.2012DFG52260)
文摘In this paper, TiN/A1Ox gated A1GaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOS- HFETs) were fabricated for gate-first process evaluation. By employing a low temperature ohmic process, ohmic contact can be obtained by annealing at 600 ℃ with the contact resistance approximately 1.6 Ω.mm. The ohmic annealing process also acts as a post-deposition annealing on the oxide film, resulting in good device performance. Those results demonstrated that the TiN/A1Ox gated MOS-HFETs with low temperature ohmic process can be applied for self-aligned gate AIGaN/GaN MOS-HFETs.
基金supported by the National Natural Science Foundation of China (Grant No. 11174182)the Specialized Research Fund for the Doctoral Program of Higher Education,China (Grant No. 20110131110005)
文摘We simulate the current-voltage (I-V) characteristics of AlGaN/AlN/GaN heterostructure field-effect transistors (HFETs) with different gate lengths using the quasi-two-dimensional (quasi-2D) model. The calculation results obtained using the modified mobility model are found to accord well with the experimental data. By analyzing the variation of the electron mobility for the two-dimensional electron gas (213EG) with the electric field in the linear region of the AlGaN/AlN/GaN HFET I-V output characteristics, it is found that the polarization Coulomb field scattering still plays an important role in the electron mobility of AlGaN/AlN/GaN HFETs at the higher drain voltage and channel electric field. As drain voltage and channel electric field increase, the 2DEG density reduces and the polarization Coulomb field scattering increases, as a result, the 2DEG electron mobility decreases.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11174182,11574182,and 61306113)the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.20110131110005)
文摘The parasitic source resistance(RS) of AlGaN/AlN/GaN heterostructure field-effect transistors(HFETs) is studied in the temperature range 300–500 K. By using the measured RSand both capacitance–voltage(C–V) and current–voltage(I–V) characteristics for the fabricated device at 300, 350, 400, 450, and 500 K, it is found that the polarization Coulomb field(PCF) scattering exhibits a significant impact on RSat the above-mentioned different temperatures. Furthermore, in the AlGaN/AlN/GaN HFETs, the interaction between the additional positive polarization charges underneath the gate contact and the additional negative polarization charges near the source Ohmic contact, which is related to the PCF scattering, is verified during the variable-temperature study of RS.
基金Projected supported by the National Natural Science Foundation of China(Grant No.11174182)the Specialized Research Fund for the Doctoral Program of Higher Education,China(Grant No.20110131110005)
文摘By making use of the quasi-two-dimensional (quasi-2D) model, the current-voltage (l-V) characteristics of In0AsA10.82N/A1N/GaN heterostructure field-effect transistors (HFETs) with different gate lengths are simulated based on the measured capacitance-voltage (C-V) characteristics and I-V characteristics. By analyzing the variation of the electron mobility for the two-dimensional electron gas (2DEG) with electric field, it is found that the different polarization charge distributions generated by the different channel electric field distributions can result in different polarization Coulomb field scatterings. The difference between the electron mobilities primarily caused by the polarization Coulomb field scatterings can reach up to 1522.9 cm2/V.s for the prepared In0.38AI0.82N/A1N/GaN HFETs. In addition, when the 2DEG sheet density is modulated by the drain-source bias, the electron mobility presents a peak with the variation of the 2DEG sheet density, the gate length is smaller, and the 2DEG sheet density corresponding to the peak point is higher.
基金supported by the National Natural Science Foundation of China(Grant Nos.51177175 and 61274039)the National Basic Research Project of China(Grant Nos.2010CB923200 and 2011CB301903)+4 种基金the Ph.D.Program Foundation of Ministry of Education of China(Grant No.20110171110021)the International Sci.&Tech.Collaboration Program of China(Grant No.2012DFG52260)the National High-tech R&D Program of China(Grant No.2014AA032606)the Science and Technology Plan of Guangdong Province,China(Grant No.2013B010401013)the Opened Fund of the State Key Laboratory on Integrated Optoelectronics(Grant No.IOSKL2014KF17)
文摘We report a novel structure of A1GaN/GaN heterostructure field effect transistors (HFETs) with a Si and Mg pair- doped interlayer grown on Si substrate. By optimizing the doping concentrations of the pair-doped interlayers, the mobility of 2DEG increases by twice for the conventional structure under 5 K due to the improved crystalline quality of the conduction channel. The proposed HFET shows a four orders lower off-state leakage current, resulting in a much higher on/off ratio ( - 10^9). Further temperature-dependent performance of Schottky diodes revealed that the inhibition of shallow surface traps in proposed HFETs should be the main reason for the suppression of leakage current.
基金supported by the National Natural Science Foundation of China(Grant Nos.11174182 and 61306113)the Specialized Research Fund for the Doctoral Program of Higher Education,China(Grant No.20110131110005)
文摘A simple and effective approach to improve the switching characteristics of AlGaN/AlN/GaN heterostructure field effect transistors (HFETs) by applying a voltage bias on the substrate is presented. With the increase of the substrate bias, the OFF-state drain current is much reduced and the ON-state current keeps constant. Both the ON/OFF current ratio and the subthreshold swing are demonstrated to be greatly improved. With the thinned substrate, the improvement of the switching characteristics with the substrate bias is found to be even greater. The above improvements of the switching characteristics are attributed to the interaction between the substrate bias induced electrical field and the bulk traps in the GaN buffer layer, which reduces the conductivity of the GaN buffer layer.
基金funded by Australian Research Council discovery project DP140103041Future Fellowship FT160100205
文摘Two-dimensional(2D) materials have attracted extensive interest due to their excellent electrical, thermal,mechanical, and optical properties. Graphene has been one of the most explored 2D materials. However, its zero band gap has limited its applications in electronic devices. Transition metal dichalcogenide(TMDC), another kind of 2D material,has a nonzero direct band gap(same charge carrier momentum in valence and conduction band) at monolayer state,promising for the efficient switching devices(e.g., field-effect transistors). This review mainly focuses on the recent advances in charge carrier mobility and the challenges to achieve high mobility in the electronic devices based on 2DTMDC materials and also includes an introduction of 2D materials along with the synthesis techniques. Finally, this review describes the possible methodology and future prospective to enhance the charge carrier mobility for electronic devices.
基金Project supported by the National Natural Science Foundation of China (Grant No. 60906037)the Fundamental Research Funds for the Central Universities,China (Grant No. ZYGX2009J027)the Foundation of State Key Laboratory of Electronic Thin Films and Integrated Devices
文摘In this paper, we present a monolithic integration of a self-protected AlGaN/GaN metal-insulator field-effect transistor (MISFET). An integrated field-controlled diode on the drain side of the AlGaN/GaN MISFET features a self- protected function for a reverse bias. This diode takes advantage of the recessed-barrier enhancement-mode technique to realize an ultra-low voltage drop and a low turn-ON voltage. In the smart monolithic integration, this integrated diode can block a reverse bias (〉 70 V/μm) and suppress the leakage current (〈 5 × 10-11 A/mm). Compared with conventional monolithic integration, the numerical results show that the MISET integrated with a field-controlled diode leads to a good performance for smart power integration. And the power loss is lower than 50% in conduction without forward current degeneration.
基金National Natural Science Foundation of China,Grant/Award Numbers:51525202,51902098,51772084,61574054,51972105the Hunan Provincial Natural Science Foundation of China(No.2018RS3051).
文摘Layered semiconductor heterostructures are essential elements in modern electronic and optoelectronic devices.Dynamically engineering the composition of these heterostructures may enable the flexible design of the properties of heterostructure-based electronics and optoelectronics as well as their optimization.Here,we report for the first time a two-step chemical vapor deposition approach for a series of WS2(1−x)Se2x/SnS2 vertical heterostructures with high-quality and large areas.The steady-state photoluminescence results exhibit an obvious composition-related quenching ratio,revealing a strong coherence between the band offset and the charge transfer efficiency at the junction interface.Based on the achieved heterostructures,dual-channel backgate field-effect transistors were successfully designed and exhibited typical composition-dependent transport behaviors,and pure n-type unipolar transistors to ambipolar transistors were realized in such systems.The direct vapor growth of these novel vertical WS2(1−x)Se2x/SnS2 heterostructures could offer an interesting system for probing new physical properties and provide a series of layered heterostructures for high-quality devices.
基金supported by the National Natural Science Foundation of China(No.11174182)the Specialized Research Fund for the Doctoral Program of Higher Education(No.20110131110005)
文摘Based on the measured capacitance–voltage(C–V) curves and current–voltage(I–V) curves for the prepared differently-sized AlN/GaN heterostructure field-effect transistors(HFETs), the I–V characteristics of the AlN/GaN HFETs were simulated using the quasi-two-dimensional(quasi-2D) model. By analyzing the variation in the electron mobility for the two-dimensional electron gas(2DEG) with the channel electric field, it is found that the different polarization charge distribution generated by the different channel electric field distribution can result in different polarization Coulomb field(PCF) scattering. The 2DEG electron mobility difference is mostly caused by the PCF scattering which can reach up to 899.6 cm^2/(V·s)(sample a), 1307.4 cm^2/(V·s)(sample b),1561.7 cm^2/(V s)(sample c) and 678.1 cm^2/(V·s)(sample d), respectively. When the 2DEG sheet density is modulated by the drain–source bias, the electron mobility for samples a, b and c appear to peak with the variation of the 2DEG sheet density, but for sample d, no peak appears and the electron mobility rises with the increase in the2 DEG sheet density.
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.
基金supported by the National Natural Science Foundation of China(No.51972007).
文摘Low-symmetry two-dimensional(2D)materials,with unique in-plane direction-dependent optical,electrical,and thermoelectric properties,have been intensively studied for their potential application values in advanced electronic and optoelectronic devices.However,since anisotropic 2D materials are highly sensitive to the environmental factors,researches on their high-performance field-effect transistors(FETs)are still limited.Here,we report a high-performance SnSe FET based on a van der Waals(vdWs)heterostructure of SnSe encapsulated in hexagonal boron nitride(/7BN)together with graphene contacts.The device exhibits a high on/off ratio exceeding 1 × 10^(9),and a carrier mobility of 118 cm^(2)·V^(-1)s^(-1).Our work highlights low-symmetry 2D SnSe holds potential to be used for designing excellent electronic devices.
基金financially supported by the National Key R&D Program of China(2018YFA0306900 and 2018YFA0305800)the National Natural Science Foundation of China(51872012)。