Based on the first-principles pseudopotentials and the plane wave energy band method,the supercells of perfect crystal 4H-SiC and those with intrinsic defects VC,VSi,VC-C and VC-Si were calculated.Ignoring the atomic ...Based on the first-principles pseudopotentials and the plane wave energy band method,the supercells of perfect crystal 4H-SiC and those with intrinsic defects VC,VSi,VC-C and VC-Si were calculated.Ignoring the atomic relaxations,the results show that the formation energy of intrinsic defects is ranked,from low to high,as VC,VC-C,VSi to VSi-Si at 0 K.The equilibrium concentration of each intrinsic defect can be deduced from the formation energy of each intrinsic defect.The concentration ranks,from high to low,as VC,VC-C,VSi,VSi-Si,which is in accordance with the ESR and PL results.The stabilizing process of metastable defects VSi converting to VC-C was explained by formation energy.展开更多
The intrinsic defects in epitaxial semi-insulating 4H-SiC prepared by low pressure chemical vapor deposition （LPCVD） are studied by electron spin resonance （ESR） with different illumination times. The results show...The intrinsic defects in epitaxial semi-insulating 4H-SiC prepared by low pressure chemical vapor deposition （LPCVD） are studied by electron spin resonance （ESR） with different illumination times. The results show that the intrinsic defects in as-grown 4H-SiC consist of carbon vacancy （Vc） and complex-compounds-related Vc. There are two other apexes presented in the ESR spectra after illumination by Xe light, which are likely to be Vsi and VcCsi. Illumination time changes the relative density of intrinsic defects in 4H-SiC; the relative density of intrinsic defects reaches a maximum when the illumination time is 2.5 min, and the ratio of Vc to complex compounds is minimized simultaneously. It can be deduced that some Vsi may be transformed to the complex-compounds-related Vc because of the illumination.展开更多
The immobilization of biomaterials on a carrier is the first step for many different applications in life science and medicine. The usage of surface-near electrostatic forces is one possible approach to guide the char...The immobilization of biomaterials on a carrier is the first step for many different applications in life science and medicine. The usage of surface-near electrostatic forces is one possible approach to guide the charged biomaterials to a specific location on the carrier. In this study, we investigate the effect of intrinsic defects on the surface potential of silicon carriers in the dark and under illumination by means of Kelvin probe force microscopy. The intrinsic defects were introduced into the carrier by local, stripe-patterned ion implantation of silicon ions with a fluence of 3 × 10<sup>13</sup> Si ions/cm<sup>2</sup> and 3 × 10<sup>15</sup> Si ions/cm<sup>2</sup> into a p-type silicon wafer with a dopant concentration of 9 × 10<sup>15</sup> B/cm<sup>3</sup>. The patterned implantation allows a direct comparison between the surface potential of the silicon host against the surface potential of implanted stripes. The depth of the implanted silicon ions in the target and the concentration of displaced silicon atoms was simulated using the Stopping and Range of Ions in Matter (SRIM) software. The low fluence implantation shows a negligible effect on the measured Kelvin bias in the dark, whereas the large fluence implantation leads to an increased Kelvin bias, i.e. to a smaller surface work function according to the contact potential difference model. Illumination causes a reduced surface band bending and surface potential in the non-implanted regions. The change of the Kelvin bias in the implanted regions under illumination provides insight into the mobility and lifetime of photo-generated electron-hole pairs. Finally, the effect of annealing on the intrinsic defect density is discussed and compared with atomic force microscopy measurements on the 2<sup>nd</sup> harmonic. In addition, by using the Baumgart, Helm, Schmidt interpretation of the measured Kelvin bias, the dopant concentration after implantation is estimated.展开更多
With annealing temperature kept at 1573 K, the effects of annealing time on stability of the intrinsic defects in epitaxial unintentionally doped 4H-SiC prepared by low pressure chemical vapour deposition have been st...With annealing temperature kept at 1573 K, the effects of annealing time on stability of the intrinsic defects in epitaxial unintentionally doped 4H-SiC prepared by low pressure chemical vapour deposition have been studied by electron spin resonance （ESR） and low temperature photoluminescence. This paper reports the results shown that annealing time has an important effect on the intrinsic defects in unintentionally doped 4H-SiC when annealing temperature kept at 1573 K. When the annealing time is less than 30 min, the intensity of ESR and photoluminescence is increasing with annealing time prolonged, and reaches the maximum when annealing time is 30 min. Then the intensity of ESR and photoluminescence is rapidly decreased with the longer annealing time, and much less than that of as-grown 4H-SiC when annealing time is 60 min, which should be related with the interaction among the intrinsic defects during the annealing process.展开更多
To study the physical origin of the non-ohmic behavior of WO3 ceramics,the effects of heat treatment in different atmospheres on WO3 varistors were investigated.Experiments showed that there was a dependence of the no...To study the physical origin of the non-ohmic behavior of WO3 ceramics,the effects of heat treatment in different atmospheres on WO3 varistors were investigated.Experiments showed that there was a dependence of the nonlinear coefficient on thermal treatment under different atmospheres.Thermal treatments in argon and oxygen atmospheres at 900℃proved this dependence,and indicated that the nonlinear coefficient got significantly lower when the samples were thermally treated under argon atmosphere.Subsequent exposure to oxygen atmosphere at the same temperature led to the restoration of electrical properties.The result shows that the physical origin of the non-ohmic behavior of WO3 ceramics is oxygen on the grain surfaces adsorbed by intrinsic defects.展开更多
The grain boundary layer behavior in ZnO/Si heterostucture is investigated. The current-voltage （I-V） curves, deep level transient spectra （DLTS） and capacitance-voltage （C-V） curves are measured. The transport ...The grain boundary layer behavior in ZnO/Si heterostucture is investigated. The current-voltage （I-V） curves, deep level transient spectra （DLTS） and capacitance-voltage （C-V） curves are measured. The transport currents ofZnO/Si heterojunction are dominated by grain boundary layer as high densities ofinterfacial states existed. The interesting phenomenon that the crossing of in I-V curves of ZnO/Si heterojunction at various measurement temperatures and the decrease of its effective barrier height with the decrement of temperature are in contradiction with the ideal heterojunction thermal emission model is observed. The details will be discussed in the following.展开更多
基金Project supported by the National Natural Science Foundation of China (No.61006060)the Scientific Research Foundation of the Ningbo Dahongying University (No.GY112111)the Scientific Research of Education Bureau of Zhejiang Province (No.Y201122504)
文摘Based on the first-principles pseudopotentials and the plane wave energy band method,the supercells of perfect crystal 4H-SiC and those with intrinsic defects VC,VSi,VC-C and VC-Si were calculated.Ignoring the atomic relaxations,the results show that the formation energy of intrinsic defects is ranked,from low to high,as VC,VC-C,VSi to VSi-Si at 0 K.The equilibrium concentration of each intrinsic defect can be deduced from the formation energy of each intrinsic defect.The concentration ranks,from high to low,as VC,VC-C,VSi,VSi-Si,which is in accordance with the ESR and PL results.The stabilizing process of metastable defects VSi converting to VC-C was explained by formation energy.
基金supported by the National Natural Science Foundation of China(No.60606022)the Advanced Fund(No.9140A08050508)the Applied Materials Innovation Fund (Nos.XA-AM-200607,XA-AM-200704)
文摘The intrinsic defects in epitaxial semi-insulating 4H-SiC prepared by low pressure chemical vapor deposition （LPCVD） are studied by electron spin resonance （ESR） with different illumination times. The results show that the intrinsic defects in as-grown 4H-SiC consist of carbon vacancy （Vc） and complex-compounds-related Vc. There are two other apexes presented in the ESR spectra after illumination by Xe light, which are likely to be Vsi and VcCsi. Illumination time changes the relative density of intrinsic defects in 4H-SiC; the relative density of intrinsic defects reaches a maximum when the illumination time is 2.5 min, and the ratio of Vc to complex compounds is minimized simultaneously. It can be deduced that some Vsi may be transformed to the complex-compounds-related Vc because of the illumination.
文摘The immobilization of biomaterials on a carrier is the first step for many different applications in life science and medicine. The usage of surface-near electrostatic forces is one possible approach to guide the charged biomaterials to a specific location on the carrier. In this study, we investigate the effect of intrinsic defects on the surface potential of silicon carriers in the dark and under illumination by means of Kelvin probe force microscopy. The intrinsic defects were introduced into the carrier by local, stripe-patterned ion implantation of silicon ions with a fluence of 3 × 10<sup>13</sup> Si ions/cm<sup>2</sup> and 3 × 10<sup>15</sup> Si ions/cm<sup>2</sup> into a p-type silicon wafer with a dopant concentration of 9 × 10<sup>15</sup> B/cm<sup>3</sup>. The patterned implantation allows a direct comparison between the surface potential of the silicon host against the surface potential of implanted stripes. The depth of the implanted silicon ions in the target and the concentration of displaced silicon atoms was simulated using the Stopping and Range of Ions in Matter (SRIM) software. The low fluence implantation shows a negligible effect on the measured Kelvin bias in the dark, whereas the large fluence implantation leads to an increased Kelvin bias, i.e. to a smaller surface work function according to the contact potential difference model. Illumination causes a reduced surface band bending and surface potential in the non-implanted regions. The change of the Kelvin bias in the implanted regions under illumination provides insight into the mobility and lifetime of photo-generated electron-hole pairs. Finally, the effect of annealing on the intrinsic defect density is discussed and compared with atomic force microscopy measurements on the 2<sup>nd</sup> harmonic. In addition, by using the Baumgart, Helm, Schmidt interpretation of the measured Kelvin bias, the dopant concentration after implantation is estimated.
基金supported by the National Natural Science Foundation of China (Grant No.60876061)Pre-Research Foundation (Grant No.9140A08050508)the 13115 Innovation Engineering of Shanxi,China (Grant No.2008ZDKG-30)
文摘With annealing temperature kept at 1573 K, the effects of annealing time on stability of the intrinsic defects in epitaxial unintentionally doped 4H-SiC prepared by low pressure chemical vapour deposition have been studied by electron spin resonance （ESR） and low temperature photoluminescence. This paper reports the results shown that annealing time has an important effect on the intrinsic defects in unintentionally doped 4H-SiC when annealing temperature kept at 1573 K. When the annealing time is less than 30 min, the intensity of ESR and photoluminescence is increasing with annealing time prolonged, and reaches the maximum when annealing time is 30 min. Then the intensity of ESR and photoluminescence is rapidly decreased with the longer annealing time, and much less than that of as-grown 4H-SiC when annealing time is 60 min, which should be related with the interaction among the intrinsic defects during the annealing process.
基金supported by the National Natural Science Foundation of China(No.50772092)
文摘To study the physical origin of the non-ohmic behavior of WO3 ceramics,the effects of heat treatment in different atmospheres on WO3 varistors were investigated.Experiments showed that there was a dependence of the nonlinear coefficient on thermal treatment under different atmospheres.Thermal treatments in argon and oxygen atmospheres at 900℃proved this dependence,and indicated that the nonlinear coefficient got significantly lower when the samples were thermally treated under argon atmosphere.Subsequent exposure to oxygen atmosphere at the same temperature led to the restoration of electrical properties.The result shows that the physical origin of the non-ohmic behavior of WO3 ceramics is oxygen on the grain surfaces adsorbed by intrinsic defects.
基金supported by the National Natural Science Foundation of China(Nos.50472009,10474091,50532070).
文摘The grain boundary layer behavior in ZnO/Si heterostucture is investigated. The current-voltage （I-V） curves, deep level transient spectra （DLTS） and capacitance-voltage （C-V） curves are measured. The transport currents ofZnO/Si heterojunction are dominated by grain boundary layer as high densities ofinterfacial states existed. The interesting phenomenon that the crossing of in I-V curves of ZnO/Si heterojunction at various measurement temperatures and the decrease of its effective barrier height with the decrement of temperature are in contradiction with the ideal heterojunction thermal emission model is observed. The details will be discussed in the following.
