Электрические и магнитные свойства дисульфида гафния, интеркалированного атомами железа

Simultaneous study of the dependences of the structural parameters, electrical, and magnetic properties of hafnium disulfide intercalated iron atoms in the dependence on the intercalate concentration and temperature has been performed for the first time. The temperature dependences of the electrical resistance are shown to exhibit the activation character with the activation energies characteristic of impurity conduction. The effective magnetic moments of iron ions in Fe_ x HfS_2 is found to be significantly lesser than the values of free iron ions and to decrease as the iron content increases. The character of the temperature dependences of the effective magnetic moments and negative values of the paramagnetic Curie temperatures indicate possible interactions of the antiferromagnetic type between intercalated atoms. However, the dependences of the magnetization on field for Fe_0.33HfS_2 and Fe_0.5HfS_2 obtained at T = 2 K demonstrate the hysteresis phenomenon characteristic of the ferromagnetic state. The results are discussed assuming the existence of hybridization 3 d electron states of intercalated iron atoms with the electronic states of HfS_2 matrices and the competition of various exchange interaction.

Impurity Conduction in Silicon Carbide

We report on admittance spectroscopy (AS) investigations taken on aluminum (Al)- doped 6H-SiC crystals at low temperatures. Admittance spectra taken on Schottky contacts of highly doped samples (NA ≥ 7.2×1017 cm-3) reveal two series of conductance peaks, which cause two different slopes of the Arrhenius plot. The steep slope is attributed to the Al acceptor, while the flatter one - obtained from the low temperature peaks - is attributed to the activation energy ε3 of nearest neighbor hopping. We propose a model, which explains the unexpected sharpness of the low temperature conductance peaks and the disappearance of these peaks for low acceptor concentrations. The model is verified by simulation, and the AS results are compared with corresponding results obtained from resistivity measurements taken on 4H- and the identical 6HSiC samples.

SiC MATERIAL PROPERTIES

This chapter briefly summarizes device-relevant material properties of the wide bandgap semiconductor silicon carbide. The polytypes 4 H -, 6 H - and 3 C - SiC are predominantly considered. These SiC polytypes can reproducibly be grown as single crystals; they have superior electronic and thermal material properties. The conductivity type can be adjusted by shallow donors and acceptors. Special sections are related to the diffusion of dopants, to the impurity conduction, to the minority carrier lifetime and to the different types of traps generated at the interface of thermally grown SiC/SiO 2 structures.