Electronic Properties of Amorphous and Crystalline Ge 2 Sb 2 Te 5 Films

Optical and electrical properties of sputtered Ge 2 Sb 2 Te 5 films in amorphous and crystalline states have been studied. The optical band-gaps of amorphous, cubic (NaCl-type), and hexagonal Ge 2 Sb 2 Te 5 are 0.74, 0.5, and 0.5 eV, respectively. Electrically, the amorphous and cubic states behave as semiconductors with activation energies of 0.45 and 0.14 eV, while the hexagonal state is metallic. The resistivity decreases slightly at the melting point of ∼600°C. All the states show p -type thermoelectric power, in which the amorphous and the cubic state have the activation energies of 0.3 and 0.14 eV. Carrier parameters and electronic densities-of-states are estimated and considered.