Semiconductor-metal and superconducting transitions induced by pressure in amorphousAs2Te3

The resistivity and activation energy $\Delta E$ in $\rho ={\rho }_0\exp \left(\frac{\Delta E}{\mathrm{kT}}\right)$ of flash evaporated amorphous ${\mathrm{As}}_2$ ${\mathrm{Te}}_3$ films were found to decrease gradually with increasing pressure until $\rho \sim 8\times {10}^{-4\mathrm{}}$ Ωcm becomes temperature independent near 100 kbar. This gradual transition contrasts with the abrupt transitions occurring at 60 kbar in $a-\mathrm{G}\mathrm{e}$ and 100 kbar in $a-\mathrm{S}\mathrm{i}$. The metallic amorphous ${\mathrm{As}}_2$ ${\mathrm{Te}}_3$ becomes superconducting at 4.4 ± 0.1 K and 100 kbar. The resistivity nearly returns to its original value after release of pressure at 300 K. The opposite sign of the pressure coefficients of the optical parameters in tetrahedral and chalcogenide materials suggests that a gradual spreading of the bands and closing of the gap occurs in chalcogenide glasses. In tetrahedral materials a sudden increase in coordination seems to take place at a critical pressure.