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31.
Steady-state and transient forward current-voltage I-V characteristics have been measured in 5.5 kV p+-n-n+ 4H-SiC rectifier diodes up to a current density j≈5.5×10 4 A/cm2. The steady-state data are compared with calculations in the framework of a model, in which the emitter injection coefficient decreases with increasing current density. To compare correctly the experimental and theoretical results, the lifetime of minority carriers for high injection level, τph, has been estimated from transient characteristics. At low injection level, the hole diffusion length Lpl has been measured by photoresponse technique. For a low-doped n-base, the hole diffusion lengths are Lpl≈2 μm and Lph≈6-10 μm at low and high injection levels respectively. Hole lifetimes for low and high injection levels are τpl≈15 ns and τph≈140-400 ns. The calculated and experimental results agree well within the wide range of current densities 10 A/cm 23 A/cm2. At j>5 kA/cm2, the experimental values of residual voltage drop V is lower than the calculated ones. In the range of current densities 5×103 A/cm24 A/cm2, the minimal value of differential resistance Rd =dV/dj is 1.5×10-4 Ω cm2. At j>25 kA/cm2, Rd increases with increasing current density manifesting the contribution of other nonlinear mechanisms to the formation steady-state current-voltage characteristic. The possible role of Auger recombination is also discussed  相似文献   
32.
The distribution of hydrogen in Si and SiC following high-temperature proton irradiation (T irr=20–700 °C) is studied by secondary-ion mass spectrometry. It is shown that the hydrogen concentration profile in SiC depends weakly on irradiation temperature. In Si appreciable alteration of the concentration profile is observed already at T irr⋍300 °C, and the profile completely loses its concentration gradient at T irr⋍700 °C. Fiz. Tekh. Poluprovodn. 33, 1409–1410 (December 1999)  相似文献   
33.
The energies of localized acceptor states in quantum wells (strained Ge layers in Ge/Ge1?x Six heterostructures) were analyzed theoretically in relation to the quantum well width and the impurity position in the well. The impurity absorption spectrum in the far IR range is calculated. Comparison of the results of the calculation with experimental photoconductivity spectra allows an estimation of the acceptor distribution in the quantum well to be made. In particular, it was concluded that acceptors may largely concentrate near the heterointerfaces. The absorption spectrum is calculated taking into account the resonance impurity states. This allows the features observed in the short-wavelength region of the spectrum to be interpreted as being due to transitions into the resonance energy levels “linked” to the upper size-quantization subbands.  相似文献   
34.
High frequency IMPATT oscillations followed under certain conditions by reversible impact ionization wave breakdown of the p +-n-n + diode structure have been experimentally observed for the first time in a drift step recovery diode operating in the avalanche breakdown mode after a fast voltage restoration of the p-n junction.  相似文献   
35.
The realizability of polarization selection of electromagnetic waves is proved. The possibility of determination of the polarization of the radiated wave even in the case an arbitrary variation in the mutual positions of transmitting and receiving antennas is shown.  相似文献   
36.
New types of two-terminal tandem solar cells DSC/c-Si in which mesoscopic dye-sensitized solar cell (DSC) was connected in parallel with a crystalline silicon (c-Si) solar cell, were developed and investigated. We have measured the optical and photovoltaic parameters for both the individual and the fabricated tandem DSC/c-Si solar cells. It was shown that the highest efficiency of 14.7% for the tandem DSC/c-Si solar cell under standard AM1.5G (100 mW/cm2) illumination conditions was achieved for DSC based on 3.5 μm thick titanium dioxide photoelectrode.  相似文献   
37.
Semiconductors - We present the results of a comparative study on behaviour of the photovoltaic parameters in perovskite (PSC), dye-sensitized (DSC) and crystalline silicon (c-Si) solar cells under...  相似文献   
38.
Previously, GaAs/AlAs superlattices with a small active area (~1 μm2) were used by us to design mixer diodes. It was established that these superlattices can efficiently be used in the terahertz (THz) range. It was theoretically and experimentally shown that short-period (i.e., containing few periods) superlattices in the composition of harmonic mixers have significant advantages in comparison with multi-period (with 50–100 or more periods) superlattices at frequencies of up to 5.3 THz. In this study, the superlattice design is optimized and the operation efficiency of short-period superlattices is shown to be determined to a large extent by the transition regions located at the superlattice edges.  相似文献   
39.
An efficient procedure for the fabrication of highly conductive carbon nanotube/graphene hybrid yarns has been developed. To start, arrays of vertically aligned multi‐walled carbon nanotubes (MWNT) are converted into indefinitely long MWNT sheets by drawing. Graphene flakes are then deposited onto the MWNT sheets by electrospinning to form a composite structure that is transformed into yarn filaments by twisting. The process is scalable for yarn fabrication on an industrial scale. Prepared materials are characterized by electron microscopy, electrical, mechanical, and electrochemical measurements. It is found that the electrical conductivity of the composite MWNT‐graphene yarns is over 900 S/cm. This value is 400% and 1250% higher than electrical conductivity of pristine MWNT yarns or graphene paper, respectively. The increase in conductivity is asssociated with the increase of the density of states near the Fermi level by a factor of 100 and a decrease in the hopping distance by an order of magnitude induced by grapene flakes. It is found also that the MWNT‐graphene yarn has a strong electrochemical response with specific capacitance in excess of 111 Fg?1. This value is 425% higher than the capacitance of pristine MWNT yarn. Such substantial improvements of key properties of the hybrid material can be associated with the synergy of MWNT and graphene layers in the yarn structure. Prepared hybrid yarns can benefit such applications as high‐performance supercapacitors, batteries, high current capable cables, and artificial muscles.  相似文献   
40.
A technology is developed for making single-chip diaphragm pressure sensors with polycrystalline-silicon piezoresistive elements on a monocrystalline-silicon substrate. It allows one to produce piezoresistive elements with a conductivity–temperature characteristic that neutralizes the temperature dependence of piezoresistive sensitivity. Sensors with a 1.8 × 1.8-mm2 diaphragm are designed and fabricated by the above technology for pressures ranging from 1 to 105 Pa, showing a maximum sensitivity of 10–6 Pa–1. The sensors are tested in aerodynamic experiments on monitoring the flow past a model wing of finite span at angles of attack close to the stall angle.  相似文献   
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