Efforts have been made to prepare nanocomposites of a-Fe2O3-ZnO by wet chemical route with varying concentrations of the precursors.The microstructural properties of the samples are investigated by powder X-ray diffra...Efforts have been made to prepare nanocomposites of a-Fe2O3-ZnO by wet chemical route with varying concentrations of the precursors.The microstructural properties of the samples are investigated by powder X-ray diffractometry（PXRD） and Transmission electron microscopy.Initial concentration of Zn ions（up to 20 at%） leads to the formation of nanocomposites of a-Fe2O3 and ZnO.Evolution of ZnFe2O4 phase is detected by the substitution of higher concentration of Zn2？（30 at%） in the sample.The average size of the nanoparticles remains in the range of 22–27 nm as obtained from XRD data.The results obtained from electron microscopic studies are also close to these values.Photoluminescence measurement shows the excitonic peak of ZnO around 390 nm which gets strengthened with Zn addition.FTIR spectra show the metal–oxygen band below 700 cm-1.Room temperature Mssbauer studies of the samples show the transition of iron oxide form antiferromagnetic state to paramagnetic state with increasing concentration of Zn2？.Sharp quenching of hyperfine field with Zn concentration is observed as the Hintvalue reduced to zero from 51 T.展开更多
A full-scale, self-consistent, non-linear, large-signal model of double-drift hetero-structure IMPATT diode with general doping profile is derived. This newly developed model, for the first time, has been used to anal...A full-scale, self-consistent, non-linear, large-signal model of double-drift hetero-structure IMPATT diode with general doping profile is derived. This newly developed model, for the first time, has been used to analyze the large-signal characteristics of hexagonal SiC-based double-drift IMPATT diode. Considering the fabrication feasibility, the authors have studied the large-signal characteristics of Si/SiC-based hetero-structure devices. Under small-voltage modulation （~ 2%, i.e. small-signal conditions） results are in good agreement with calculations done using a linearised small-signal model. The large-signal values of the diode＇s negative conductance （5 × 106 S/m2）, susceptance （10.4 × 107 S/m2）, average breakdown voltage （207.6 V）, and power generating efficiency （15%, RF power： 25.0 W at 94 GHz） are obtained as a function of oscillation amplitude （50% of DC breakdown voltage） for a fixed average current density. The large-signal calculations exhibit power and efficiency saturation for large-signal （〉 50%） voltage modulation and thereafter decrease gradually with further increasing voltage-modulation. This generalized large-signal formulation is applicable for all types of IMPATT structures with distributed and narrow avalanche zones. The simulator is made more realistic by incorporating the space-charge effects, realistic field and temperature dependent material parameters in Si and SiC. The electric field snap-shots and the large-signal impedance and admittance of the diode with current excitation are expressed in closed loop form. This study will act as a guide for researchers to fabricate a high-power Si/SiC-based IMPATT for possible application in high-power MM-wave communication systems.展开更多
Static and dynamic properties of both complementary n-Ge/p-Si and p-Ge/n-Si hetero-junction DoubleDrift IMPATT diodes have been investigated by an advanced and realistic computer simulation technique, devel- oped by t...Static and dynamic properties of both complementary n-Ge/p-Si and p-Ge/n-Si hetero-junction DoubleDrift IMPATT diodes have been investigated by an advanced and realistic computer simulation technique, devel- oped by the authors, for operation in the Ka-, V- and W-band frequencies. The results are further compared with corresponding Si and Ge homo-junction devices. The study shows high values of device efficiency, such as 23%, 22% and 21.5%, for n-Ge/p-Si IMPATTs at the Ka, V and W bands, respectively. The peak device negative con- ductances for n-Si/p-Ge and n-Ge/p-Si hetero-junction devices found to be 50.7× 10^6 S/m^2 and 71.3× 106 S/m^2, which are -3-4 times better than their Si and Ge counterparts at the V-band. The computed values of RF powerdensity for n-Ge/p-Si hetero-junction IMPATTs are 1.0 ×10^9, 1.1 × 10^9 and 1.4× 10^9 W/m^2, respectively, for Ka-, V- and W-band operation, which can be observed to be the highest when compared with Si, Ge and n-Si/p-Ge devices. Both of the hetero-junctions, especially the n-Ge/p-Si hetero-junction diode, can thus become a superior RF-power generator over a wide range of frequencies. The present study will help the device engineers to choose a suitable material pair for the development of high-power MM-wave IMPATT for applications in the civil and defense-related arena.展开更多
文摘Efforts have been made to prepare nanocomposites of a-Fe2O3-ZnO by wet chemical route with varying concentrations of the precursors.The microstructural properties of the samples are investigated by powder X-ray diffractometry（PXRD） and Transmission electron microscopy.Initial concentration of Zn ions（up to 20 at%） leads to the formation of nanocomposites of a-Fe2O3 and ZnO.Evolution of ZnFe2O4 phase is detected by the substitution of higher concentration of Zn2？（30 at%） in the sample.The average size of the nanoparticles remains in the range of 22–27 nm as obtained from XRD data.The results obtained from electron microscopic studies are also close to these values.Photoluminescence measurement shows the excitonic peak of ZnO around 390 nm which gets strengthened with Zn addition.FTIR spectra show the metal–oxygen band below 700 cm-1.Room temperature Mssbauer studies of the samples show the transition of iron oxide form antiferromagnetic state to paramagnetic state with increasing concentration of Zn2？.Sharp quenching of hyperfine field with Zn concentration is observed as the Hintvalue reduced to zero from 51 T.
文摘A full-scale, self-consistent, non-linear, large-signal model of double-drift hetero-structure IMPATT diode with general doping profile is derived. This newly developed model, for the first time, has been used to analyze the large-signal characteristics of hexagonal SiC-based double-drift IMPATT diode. Considering the fabrication feasibility, the authors have studied the large-signal characteristics of Si/SiC-based hetero-structure devices. Under small-voltage modulation （~ 2%, i.e. small-signal conditions） results are in good agreement with calculations done using a linearised small-signal model. The large-signal values of the diode＇s negative conductance （5 × 106 S/m2）, susceptance （10.4 × 107 S/m2）, average breakdown voltage （207.6 V）, and power generating efficiency （15%, RF power： 25.0 W at 94 GHz） are obtained as a function of oscillation amplitude （50% of DC breakdown voltage） for a fixed average current density. The large-signal calculations exhibit power and efficiency saturation for large-signal （〉 50%） voltage modulation and thereafter decrease gradually with further increasing voltage-modulation. This generalized large-signal formulation is applicable for all types of IMPATT structures with distributed and narrow avalanche zones. The simulator is made more realistic by incorporating the space-charge effects, realistic field and temperature dependent material parameters in Si and SiC. The electric field snap-shots and the large-signal impedance and admittance of the diode with current excitation are expressed in closed loop form. This study will act as a guide for researchers to fabricate a high-power Si/SiC-based IMPATT for possible application in high-power MM-wave communication systems.
文摘Static and dynamic properties of both complementary n-Ge/p-Si and p-Ge/n-Si hetero-junction DoubleDrift IMPATT diodes have been investigated by an advanced and realistic computer simulation technique, devel- oped by the authors, for operation in the Ka-, V- and W-band frequencies. The results are further compared with corresponding Si and Ge homo-junction devices. The study shows high values of device efficiency, such as 23%, 22% and 21.5%, for n-Ge/p-Si IMPATTs at the Ka, V and W bands, respectively. The peak device negative con- ductances for n-Si/p-Ge and n-Ge/p-Si hetero-junction devices found to be 50.7× 10^6 S/m^2 and 71.3× 106 S/m^2, which are -3-4 times better than their Si and Ge counterparts at the V-band. The computed values of RF powerdensity for n-Ge/p-Si hetero-junction IMPATTs are 1.0 ×10^9, 1.1 × 10^9 and 1.4× 10^9 W/m^2, respectively, for Ka-, V- and W-band operation, which can be observed to be the highest when compared with Si, Ge and n-Si/p-Ge devices. Both of the hetero-junctions, especially the n-Ge/p-Si hetero-junction diode, can thus become a superior RF-power generator over a wide range of frequencies. The present study will help the device engineers to choose a suitable material pair for the development of high-power MM-wave IMPATT for applications in the civil and defense-related arena.
