Papers by Keyword: Hall Coefficient

Abstract: We investigate the temperature-dependent resistivity (ρ(T)) and Hall coefficient (R_H(T)) of heavily Al-doped 4H-SiC and discuss the underlying conduction mechanisms. The sign of R_H(T) changes from positive to negative in nearest-neighbor hopping (NNH) and variable-range hopping (VRH) conduction, whereas it is positive in band conduction because Al-doped 4H-SiC is a p-type semiconductor. We propose a general physical model to explain why R_H(T) in hopping conduction becomes negative at low temperatures, which is applicable to both NNH and VRH conduction. Moreover, we elucidate why the activation energy for negative R_H(T) becomes similar to that of ρ(T) in NNH conduction.

Abstract: Controlling the polymerization of polypyrrole (Ppy) in presence of Zr-based metal organic-framework (Zr-MOFs) using sodium dodecyl sulphonate (SDS) as a dopant, leads to the formation of a new class of thermoelectric materials based on conducting polymer and highly porous MOFs with enhanced properties for energy production applications. The polymerization of polypyrrole in the Zr-Fumerate pores leads to the formation of homogenously coated MOF-spheres with high crystalinity and a high degree of improvement in many electrical properties such as conductivity and carrier mobility. The figure shows the movement of the electrons from the hot to the cold side in the aligned polymer inside the MOF pores.

Abstract: The relative metallic character of noble metals, Cu, Ag & Au has been suggested by their physical and chemical properties. Their position in the metallic series is in the neighborhood of that of Li, Mg and Zn. These Metals are inferior of Li, Mg, Zn, Fe, Co and Ni in metallic character. Li, Mg, Zn, Fe, Co and Ni are inferior to Na, K, Rb, Cs, Ca, Ba and Sr. The noble metals have simple metallic character in physical properties at normal temperatures.

Abstract: We investigate the temperature dependence of the resistivity and Hall coefficient for heavily Al-doped p-type 4H-SiC epilayers with Al concentrations (C_Al) of > 2E19 cm^−3, which are substrates for the collectors of insulated-gate bipolar transistors. The signs of the measured Hall co- efficients (R_H) changed from positive to negative at low temperatures. For epilayers with C_Al values of < 3E19 cm^−3, a negative R_H was observed in the hopping conduction region. In contrast, for epilayers with C_Al values of > 3E19 cm^−3, a negative R_H was observed in not only the hopping conduction region but also the band conduction region, which is a striking feature because the movement of free holes in the valence band should make R_H positive. For an epilayer with C_Al of 1.8E20 cm^−3, the sign of R_H clearly changed three times in the band conduction region. Moreover, the activation energies of the temperature-dependent R_H values were similar to those of the temperature-dependent resistivity in the corresponding temperature ranges, irrespective of the conduction mechanisms (band and hopping conduction).

Abstract: The temperature dependencies of the resistivity and Hall coefficient for heavily Al-doped 4H-SiC epilayers with Al concentration (C_Al) higher than 2×10¹⁹ cm^-3 were investigated. The signs of measured Hall coefficients (R_H) change from positive to negative at low temperatures. For the epilayers with C_Al < 3×10¹⁹ cm^-3 the sign inversion occurred in the hopping conduction region, which was reported to be explicable using the model for amorphous semiconductors. For the epilayers with C_Al > 3×10¹⁹ cm^-3, on the other hand, the sign inversion occurred in the band conduction region, which is a striking feature, because the movement of free holes in the valence band should make R_H positive. The sign-inversion temperature increased with increasing C_Al, while the dominant-conduction-mechanism-change temperature was almost independent of C_Al.

Abstract: Thin films of a composite of molybdenum disilicide (MoSi₂) and silicon (Si) were fabricated by radio frequency magnetron sputtering using a target made of a powder mixture of MoSi₂ and Si with a Si-to-Mo molar ratio of 1:X (2.0 X 2.5). The Hall coefficients were measured to identify the conduction mechanisms in the thin films. The sign and magnitude of the Hall coefficients revealed that thin films with X = 2.02.2 having a hexagonal crystal structure showed p-type conduction, while the mechanism for the n-type film with X = 2.33 was unknown and that for a composite of hexagonal and an unknown structure with X = 2.3, 2.4 and 2.5 showed mixed conduction.

Abstract: Nanostructured films are considered as a characteristic (distinctive) type of consolidated nanostructured materials (NMs). Their benefits as compared to other types of NMs are described in detail. Some new interesting results related to mechanical and physical properties of nanostructured films based on high-melting point compounds (nitrides, borides and carbides), metals, and oxides are discussed. Data on film hardness, type of deformation, effect of additional magnetic field at deposition of films, properties of twins, conductivity, coercivity, and the Hall coefficient are reported and commented.