Scanning tunneling microscopy and spectroscopy of the phase change alloy Ge1Sb2Te4

Scanning tunneling microscopy and spectroscopy have been employed to reveal the evolution of the band gap and the Fermi level as a function of the annealing temperature for Ge1Sb2Te4, a promising material for phase change memory applications. The band gap decreases continuously from 0.65 eV in the amorphous phase via 0.3 eV in the metastable crystalline phase to zero gap in the stable crystalline phase. The Fermi level moves from the center of the gap in the amorphous phase close to the valence band within the crystalline phases. Moreover, the metastable phase has been imaged with atomic resolution, presumably showing the Te lattice at negative sample bias and the Ge/Sb/vacancy lattice at positive bias.