The mechanism of memory and threshold switching in (GeTe4)100−x(As2Se3)x glasses

Electrical switching in (GeTe ₄) _{100 − x}(As ₂Se ₃) _x glasses in the range (0 ≤ x ≤ 40) having fixed network connectivity with average coordination number (Z _av = 2.4) has been studied. Addition of As ₂Se ₃ to GeTe ₄ changes the switching type from memory to threshold for x > 10. Irrespective of the switching type, all the compositions in the system show crystallization upon heating. Samples annealed at their respective crystallization temperatures show the appearance of GeTe and Te crystallites for 0 ≤ x ≤ 10 and only Te for 15 ≤ x ≤ 40. The glasses heated to its melting temperature and quenched in water at 28 °C show GeTe and Te crystalline phases for 0 ≤ x ≤ 10 and amorphous structure for x ≥ 15. Based on this, we propose that the material in between the electrodes may melt to form a filament at the time of switching. The filament consists of temporary (high resistive amorphous) and permanent (high conducting crystalline) units. The filament is dominated by the permanent units in the memory switching compositions and by the temporary units in the threshold switching compositions. The present studies provide a unique way to understand the threshold and memory switching exhibited by chalcogenide glasses, by the thermal model and the filament formation.