Spectroscopic study of the metal-insulator transition in Ge₂Sb₂Te_(5-5x)Se_5x phase change materials

Phase Change Materials (PCMs) undergo a reversible yet swift crystal-to-amorphous transition (CAT) due to increasing temperature and various other stimuli. This CAT is typically accompanied by a metal-to-insulator transition (MIT), which is supposedly responsible for a remarkable variation of optical and electronic properties across the CAT. These material property contrasts make the PCMs attractive candidate materials for futuristic memory and optoelectronic applications. Ge₂Sb₂Te₅ (GST) is one of the extensively studied PCMs. Optimization of the rate of crystallization along with thermal stability, and enhancement in the contrast of electrical resistivity across the MIT are some of the critical material issues pertaining to the widespread application of GST in device architectures. Recent studies suggest that Ge₂Sb₂Te_(5-5x)Se_5x (GSST),i.e, Se doped GST, could be a better choice since they offer (i) lower crystalline temperature and (ii) higher contrast between electrical resistivities during MIT across the CAT. Using a combination of spectroscopic measurements via Angle Resolved Photoemission Spectroscopy (ARPES) and transport measurements we studied the MIT in a series of GSST bulk samples. Our studies show evidence for the significance of electronic inhomogeneity and the possible existence of multiple mobility edges in the vicinity of the MIT in GSST.