Observation of carrier localization in cubic crystalline Ge2Sb2Te5 by field effect measurement

Abstract

The tunable disorder of vacancies upon annealing is an important character of crystalline phase-change material Ge2Sb2Te5 (GST). A variety of resistance states caused by different degrees of disorder can lead to the development of multilevel memory devices, which could bring a revolution to the memory industry by significantly increasing the storage density and inspiring the neuromorphic computing. This work focuses on the study of disorder-induced carrier localization which could result in multiple resistance levels of crystalline GST. To analyze the effect of carrier localization on multiple resistant levels, the intrinsic field effect (the change in surface conductance with an applied transverse electric field) of crystalline GST was measured, in which GST films were annealed at different temperatures. The field effect measurement is an important complement to conventional transport measurement techniques. The field effect mobility was acquired and showed temperature activation, a hallmark of carrier localization. Based on the relationship between field effect mobility and annealing temperature, we demonstrate that the annealing shifts the mobility edge towards the valence-band edge, delocalizing more carriers. The insight of carrier transport in multilevel crystalline states is of fundamental relevance for the development of multilevel phase change data storage.

Phase change thin films for non-volatile memory applications

“…The field effect mobility increases with increasing annealing temperature of the GST225 alloy. 88 Since the increase in mobility is mainly due to the proportional reduction of localized carriers, the ordering of vacancies in GST alloys results in the delocalization of carriers, confirming theoretical predictions well.…”

Application of Ge2Sb2Te5 phase change films in flexible memory devices

“…The multiple bending cycles do not result in significant changes in the diffraction peaks of the S p films. 24–26 In addition, the diffraction peaks become broader as the number of bending cycles increases. So as to compare the grain sizes, we calculated the grain size by means of the Scherrer formula: 27 D hkl = 0.943 λ /( β cos θ )where D hkl , λ , β , and θ represent the grain size, the X-ray wavelength (0.1540 nm), the half-height width of the diffraction peak, and the Bragg diffraction angle, respectively.…”

Phase Change Behavior and Multi-Level Storage for V2O5 Thin Film in Phase-Change Memory Application

“…The first slope ① is steeper, possibly being ascribed to the precipitation of some V elements accompanied with the escaping of some oxygen atoms on the surface of thin film during heating. 8 With further heating, the resistance ② decreases gradually before an abrupt drop. It is worth noting that there is an intermediate resistance state ③ between ② and ④ in the process of crystallization.…”