Significant enhancement of ferromagnetism in Zn1−x_{1-x}Crx_{x}Te doped with iodine as an n-type dopant

The effect of additional doping of charge impurities was investigated in a ferromagnetic semiconductor Zn$_{1-x}$Cr$_{x}$Te. It was found that the doping of iodine, which is expected to act as an n-type dopant in ZnTe, brought about a drastic enhancement of the ferromagnetism in Zn$_{1-x}$Cr$_{x}$Te while the grown films remained electrically insulating. In particular, at a fixed Cr composition of x = 0.05, the ferromagnetic transition temperature Tc increased up to 300K at maximum due to the iodine doping from Tc = 30K of the undoped counterpart, while the ferromagnetism disappeared due to the doping of nitrogen as a p-type dopant. The observed systematic correlation of ferromagnetism with the doping of charge impurities of both p- and n-type, suggesting a key role of the position of Fermi level within the impurity d-state, is discussed on the basis of the double exchange interaction as a mechanism of ferromagnetism in this material.Comment: 5 figures, to be published in Phys. Rev. Let

Explosive crystallization starting from an amorphous-silicon surface region during long pulsed-laser irradiation

A newly developed method of backside time-resolved reflectivity measurement is useful for probing the interface between solid and transient liquid Si. Measurements indicate that explosive crystallization starts very near the Si surface from a highly undercooled liquid Si layer thinner than 3 nm for laser irradiation with long pulses ranging from 65 to 200 ns. During the laser irradiation, surface melt-in continues into fine-grained polycrystalline Si produced by explosive crystallization, followed by solidification of the surface-liquid layer