Anomalous Conduction between the Band and Nearest-Neighbor Hopping Conduction Regions in Heavily Al-Doped p-Type 4H-SiC

We measure the temperature-dependent resistivity (ρ(T)) for thick heavily Al- and Ncodoped p-type 4H-SiC samples grown by chemical vapor deposition (CVD), physical vapor transport (PVT), and solution growth (SG), and investigate their conduction mechanisms. For samples with an Al concentration (CAl) of 3.5×1019 to 1×1020 cm-3 grown by CVD, PVT, and SG, the conduction mechanisms at high and low temperatures are band and nearest-neighbor hopping (NNH) conduction, respectively. In the range CAl of 1×1019 to 3.5×1019 cm-3, on the other hand, an anomalous conduction, referred to as X conduction here, is observed between the band and NNH conduction regions for the samples grown by CVD and PVT, but not those grown by SG. One of the differences between the samples grown by CVD and PVT and those grown by SG is the off-orientation toward [11-20] of the (0001) 4H-SiC substrate. We discuss the reason for the appearance of X conduction, which appears to be consistent with dopant-concentration inhomogeneity model.

Regularities of microdefect formation in silicon during heat treatment for internal getter synthesis

Gettering is defined as a process by which metal impurities in the device region are reduced by localizing them in predetermined, passive regions of the silicon wafer. Internal or intrinsic gettering is an effective way to reduce the contamination in active regions. The generation of internal getters is based on the decomposition of the supersaturated oxygen solid solution in silicon, which favours the formation of a complex defect system in silicon that consists of various precipitate/dislocation agglomerates. Regularities of microdefect formation during oxygen solid solution decomposition in silicon have been studied. We show that actual solid solution supersaturation, temperature and heat treatment duration determine the structure of the solid solution. Combining these factors, including heat treatment parameters, one can control solid solution decomposition rate and SiOx precipitate sizes and quantity. The methods of X-ray diffuse scattering and transmission electron microscopy have shown high efficiency for studying the effect of heat treatment in crystals. For annealing at 450 °C, solid solution decomposition occurs at high supersaturation degrees, and concentration inhomogeneity regions may form at an early decomposition stage over the actual annealing time (up to 40 h). With an increase in the temperature of subsequent annealing to 650 °C, local regions with above-average oxygen supersaturation degrees increase the efficiency of oxygen solid solution decomposition. Further, an increase in annealing temperature to T > 1000 °С results in a more intense generation of the largest precipitates at the expense of the smaller ones. Once the precipitate sizes become sufficiently large, the elastic stresses start to relax, leading to partial incoherence and the generation of dislocations around the particles. This type of defect structure seems to be the most efficient getter.

The Influence of Step-By-Step Air Exposition of the Zr-Mn-Cr-Ni-V Alloy on Cycle Life

In the course of the research it was determined that step-by-step air exposition of the Zr-Mn-Cr-Ni-V alloy (in the form of ingot and powder) facilitating the formation of concentration inhomogeneity significantly increases the cycle life of electrodes. An electrode compacted of step-by-step exposited ingot of the alloy demonstrates no loss of capacity during 190 cycles. With the decrease of porosity, caused by adding the nickel powder with significantly smaller particle size than that of particles of the alloy, or by increase of plasticizer content from 5 % to 10 %, the electrodes are being destroyed much sooner due to formation of more dense packing.Based on the polarization curves of the researched alloy and manganese that demonstrate similar electrochemical behavior in non-oxidized state and stability in oxidized state, the conclusion is made that the increased stability and, as a consequence, the cycle life of the air-exposited alloy is mainly achieved due to manganese which is stably passive in oxidized state.

Model of Fracture, Friction, and Wear Phenomena of Porous Iron

Mechanical and tribotechnical features of powdered materials are strongly influenced by pore volume, fracture character, impurities, alloying, concentration inhomogeneity, friction conditions, and other factors. Pores also have influence on acceleration of diffusion processes and reduce undercooled austenite resistance. Annealed in hydrogen, ultra pure iron powder was used to study porous iron features. Toughness fracture and tribotechnical features had nonmonotonic dependence from porosity different from all known dependences got from technical iron powders. Researches brought out the fact that in process of porosity reduction by pressing and annealing cycles, the average dimension of porous is changed. According to the analysis of porous structure were created models of friction, wear, and fracture of pure porous iron.