Composition-Dependent Functionality of Threshold Switching Behavior in Amorphous Ge–Te Binary System

Amorphous chalcogenides, including Ge–Te binary system, exhibit distinct threshold switching behaviors essential for memory and selector applications. This study explores the threshold switching mechanisms in Te-rich Ge–Te compositions, systematically identifying key factors differentiating ovonic threshold switching (OTS) from phase change memory (PCM) functionality. Experimental results reveal that Te-rich compositions exhibit OTS behavior, characterized by reversible resistive switching at threshold voltages ranging from 1.2 to 1.6 V. In contrast, compositions near stoichiometric (GeTe) display PCM behavior, undergoing irreversible crystallization at a higher threshold voltage (∼5.0 V). Optical and electrical measurements correlate these behaviors with variations in band gap and trap depth. Our findings indicate that the difference in functionality is reflected in the relative position of the Fermi level with respect to the conduction band minimum: OTS materials exhibit deeper trap states, while PCM compositions have shallower trap states. This insight into the electronic structure provides a foundation for optimizing material properties to enhance the performance of next-generation memory and selector devices.