We study the adsorption of zigzag graphene nanoribbons （GNRs） on Si（001） substrates using the first-principles density functional theory, exploring the effects of the interface interaction on the structurM and ele...We study the adsorption of zigzag graphene nanoribbons （GNRs） on Si（001） substrates using the first-principles density functional theory, exploring the effects of the interface interaction on the structurM and electronic prop- erties of both GNRs and the substrate. By comparing the adsorption structures predicted by the local density approximation, the generalized gradient approximation, and the DFT-D2 approach, we confirm that both edge and inner C atoms of GNRs can form covalent bonds with the substrate. The GNR/substrate interaction destroys the antiferromagnetic coupling of the edge states in GNB.s. The charge transfer from the substrate to GNRs exhibits a complicated pattern and is mainly localized near the C-Si bonds. We also observe a strong perturbation of the surface states and a surface reconstruction transition induced by the GNR adsorption.展开更多
A high quality of GaAs crystal growth in nanoscale V-shape trenches on Si（O01） substrates is achieved by using the aspect-ratio trapping method. GaAs thin films are deposited via metal-organic chemical vapor deposit...A high quality of GaAs crystal growth in nanoscale V-shape trenches on Si（O01） substrates is achieved by using the aspect-ratio trapping method. GaAs thin films are deposited via metal-organic chemical vapor deposition by using a two-step growth process. Threading disJocations arising from lattice mismatch are trapped by laterally confining sidewalls, and antiphase domains boundaries are completely restricted by V-groove trenches with Si { 111} facets. Material quality is confirmed by scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and high resolution X-ray diffraction. Low temperature photoluminescence （PL） measurement is used to analyze the thermal strain relaxation in GaAs layers. This approach shows great promise for the realization of high mobility devices or optoelectronie integrated circuits on Si substrates.展开更多
The fabrication and characterization of strained-Si material grown on a relaxed Si0.79 Ge0.21/graded Si1-x- Gex/Si virtual substrate, using reduced pressure chemical vapor deposition, are presented. The Ge concentrati...The fabrication and characterization of strained-Si material grown on a relaxed Si0.79 Ge0.21/graded Si1-x- Gex/Si virtual substrate, using reduced pressure chemical vapor deposition, are presented. The Ge concentration of the constant composition SiGe layer and the grading rate of the graded SiGe layer are estimated with double-crystal X-ray diffraction and further confirmed by SIMS measurements. The surface root mean square roughness of the strained Si cap layer is 2.36nm,and the strain is about 0.83% as determined by atomic force microscopy and Raman spectra, respectively. The threading dislocation density is on the order of 4 × 10^4cm^-2. Furthermore, it is found that the stress in the strained Si cap layer is maintained even after the high thermal budget process, nMOSFET devices are fabricated and measured in strained-Si and unstrained bulk-Si channels. Compared to the co-processed bulk-Si MOSFETs at room temperature,a significant low vertical field mobility enhancement of about 85% is observed in the strained-Si devices.展开更多
Direct growth of GaN films on Si(001) substrate at low temperatures (620～720℃) by electron cyclotron resonance (ECR) microwave plasma enhanced metalorganic chemical vapor deposition (PEMOCVD).The crystalline phase s...Direct growth of GaN films on Si(001) substrate at low temperatures (620～720℃) by electron cyclotron resonance (ECR) microwave plasma enhanced metalorganic chemical vapor deposition (PEMOCVD).The crystalline phase structures of the films are investigated.The results of high resolution transmission electron microscopy (HRTEM) and X ray diffraction (XRD) indicate that high c axis oriented crystalline wurtzite GaN is grown on Si(001) but there is an amorphous layer formed naturally at GaN/Si interface.Both faces of the amorphous layer are flat and sharp,and the thickness of the layer is 2nm approximately cross the interface.The analysis supports that β GaN phase is not formed owing to the N x Si y amorphous layer induced by the reaction between N and Si during the initial nucleation stage.The results of XRD and atomic force microscopy (AFM) indicate that the conditions of substrate surface cleaned in situ by hydrogen plasma,GaN initial nucleation and subsequent growth are very important for the crystalline quality of GaN films.展开更多
A CMOS FinFET fabricated on bulk silicon substrate is demonstrated.Besides owning a FinFET structure similar to the original FinFET on SOI,the device combines a grooved planar MOSFET in the Si substrate and the fabric...A CMOS FinFET fabricated on bulk silicon substrate is demonstrated.Besides owning a FinFET structure similar to the original FinFET on SOI,the device combines a grooved planar MOSFET in the Si substrate and the fabrication processes are fully compatible with conventional CMOS process,including salicide technology.The CMOS device,inverter,and CMOS ring oscillator of this structure with normal poly silicon and W/TiN gate electrode are fabricated respectively.Driving current and sub threshold characteristics of CMOS FinFET on Si substrate with actual gate length of 110nm are studied.The inverter operates correctly and minimum per stage delay of 201 stage ring oscillator is 146ps at V d=3V.The result indicates the device is a promising candidate for the application of future VLSI circuit.展开更多
基金Supported by the National Natural Science Foundation of China under Grant No 11204296the National Basic Research Program of China under Grant No 2013CB933304
文摘We study the adsorption of zigzag graphene nanoribbons （GNRs） on Si（001） substrates using the first-principles density functional theory, exploring the effects of the interface interaction on the structurM and electronic prop- erties of both GNRs and the substrate. By comparing the adsorption structures predicted by the local density approximation, the generalized gradient approximation, and the DFT-D2 approach, we confirm that both edge and inner C atoms of GNRs can form covalent bonds with the substrate. The GNR/substrate interaction destroys the antiferromagnetic coupling of the edge states in GNB.s. The charge transfer from the substrate to GNRs exhibits a complicated pattern and is mainly localized near the C-Si bonds. We also observe a strong perturbation of the surface states and a surface reconstruction transition induced by the GNR adsorption.
基金Supported by the National Science and Technology Major Project of China under Grant No 2011ZX02708
文摘A high quality of GaAs crystal growth in nanoscale V-shape trenches on Si（O01） substrates is achieved by using the aspect-ratio trapping method. GaAs thin films are deposited via metal-organic chemical vapor deposition by using a two-step growth process. Threading disJocations arising from lattice mismatch are trapped by laterally confining sidewalls, and antiphase domains boundaries are completely restricted by V-groove trenches with Si { 111} facets. Material quality is confirmed by scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and high resolution X-ray diffraction. Low temperature photoluminescence （PL） measurement is used to analyze the thermal strain relaxation in GaAs layers. This approach shows great promise for the realization of high mobility devices or optoelectronie integrated circuits on Si substrates.
文摘The fabrication and characterization of strained-Si material grown on a relaxed Si0.79 Ge0.21/graded Si1-x- Gex/Si virtual substrate, using reduced pressure chemical vapor deposition, are presented. The Ge concentration of the constant composition SiGe layer and the grading rate of the graded SiGe layer are estimated with double-crystal X-ray diffraction and further confirmed by SIMS measurements. The surface root mean square roughness of the strained Si cap layer is 2.36nm,and the strain is about 0.83% as determined by atomic force microscopy and Raman spectra, respectively. The threading dislocation density is on the order of 4 × 10^4cm^-2. Furthermore, it is found that the stress in the strained Si cap layer is maintained even after the high thermal budget process, nMOSFET devices are fabricated and measured in strained-Si and unstrained bulk-Si channels. Compared to the co-processed bulk-Si MOSFETs at room temperature,a significant low vertical field mobility enhancement of about 85% is observed in the strained-Si devices.
文摘Direct growth of GaN films on Si(001) substrate at low temperatures (620～720℃) by electron cyclotron resonance (ECR) microwave plasma enhanced metalorganic chemical vapor deposition (PEMOCVD).The crystalline phase structures of the films are investigated.The results of high resolution transmission electron microscopy (HRTEM) and X ray diffraction (XRD) indicate that high c axis oriented crystalline wurtzite GaN is grown on Si(001) but there is an amorphous layer formed naturally at GaN/Si interface.Both faces of the amorphous layer are flat and sharp,and the thickness of the layer is 2nm approximately cross the interface.The analysis supports that β GaN phase is not formed owing to the N x Si y amorphous layer induced by the reaction between N and Si during the initial nucleation stage.The results of XRD and atomic force microscopy (AFM) indicate that the conditions of substrate surface cleaned in situ by hydrogen plasma,GaN initial nucleation and subsequent growth are very important for the crystalline quality of GaN films.
文摘A CMOS FinFET fabricated on bulk silicon substrate is demonstrated.Besides owning a FinFET structure similar to the original FinFET on SOI,the device combines a grooved planar MOSFET in the Si substrate and the fabrication processes are fully compatible with conventional CMOS process,including salicide technology.The CMOS device,inverter,and CMOS ring oscillator of this structure with normal poly silicon and W/TiN gate electrode are fabricated respectively.Driving current and sub threshold characteristics of CMOS FinFET on Si substrate with actual gate length of 110nm are studied.The inverter operates correctly and minimum per stage delay of 201 stage ring oscillator is 146ps at V d=3V.The result indicates the device is a promising candidate for the application of future VLSI circuit.
