Low Critical Concentration of Metal-Insulator Transition of Vanadium Doped Amorphous Boron

The metal–insulator transition (MIT) of V- and Zr-doped amorphous boron films (V x B 100- x , Zr x B 100- x ) was studied. The temperature dependences of the electrical conductivity, the X-ray diffraction patterns and the X-ray absorption fine structures were measured for the samples. The compositional boundary of the metal–insulator transition is found between x = 2.9 and 3.7 in V x B 100- x , and between x = 11 and 14 in Zr x B 100- x . It is considered that at the transition, the network of B 12 icosahedral clusters remains unchanged for V-doped films, while the network changes into an intermetallic compound-like structure for Zr-doped films. The low concentration of vanadium and no structural change for the transition of V-doped films are peculiar, while the critical concentration of Zr and the structural change of Zr-doped films are similar to those of transition-metal-doped amorphous silicon or germanium. The origin of the peculiarity of MIT for the V-doped films is discussed in relation to the meta...