Ultralow threshold voltage in an epitaxial <i>p</i>-GeFeTe/<i>n</i>-Si heterojunction enabled by magnetic field modulation

Abstract

Heterostructure diode architectures incorporating phase change materials (PCMs) have recently emerged as strong candidates for next-generation phase change random access memory (PCRAM) technology. However, the close proximity between the turn-on threshold voltage (Vth) of p-n heterostructures and the phase change voltage (Vpc) results in a critically narrow operational voltage window, significantly limiting device reliability. In this study, we present a breakthrough in epitaxial p-GeFeTe/n-Si heterojunction engineering through magnetic field-mediated control of Vth. The p-GeFeTe/n-Si heterojunction exhibits exponential current density–voltage (J–V) behavior with a Vth of 0.95 V. Analysis of the semilogarithmic ln(J)–V curve reveals three distinct linear regions, each characterized by a different ideality factor (ηd1, ηd2, and ηd3). As the magnetic field strength (H) increases, the differences among these ideality factors diminish, ultimately converging into a single linear region at H = 45 kOe. Under this magnetic field, an ultralow Vth of 0.27 V is achieved—representing a 72% reduction compared to operation without a magnetic field. This magneto-responsive J–V behavior is attributed to spin-split band structures that induce a field-modulated semiconductor-to-half-metal phase transition, as explained by a band alignment model. These findings offer a viable strategy for widening the operational voltage window of PCRAM and pave the way for multifunctional PCM-based devices.