Structural destabilization and optoelectronic degradation of crystalline Ge₂Sb₂Te₅ phase-change memory in low-earth orbit: A multiscale simulation study

The development of radiation-tolerant phase-change memories is essential for next-generation space technologies, yet their structural and optoelectronic responses to electron irradiation in low-Earth-orbit (LEO) environments remain insufficiently understood. In this work, we integrate ab initio molecular dynamics (AIMD) with Monte Carlo (MC) simulations to uncover the atomistic damage mechanisms governing crystalline Ge₂Sb₂Te₅ (GST). Our directional and sublayer-resolved analyses show that radiation susceptibility and resilience are strongly governed by variations in Milliken bond populations (MBP) and the corresponding local bonding strengths within the GST lattice. Notably, van der Waals (vdW) planes with higher MBP act as defect sinks, buffering displacement cascades at threshold levels. AIMD simulations reveal lower energy damage thresholds for Te primary knock-on atoms (PKAs) than for Sb and Ge, leading to earlier onset of order–disorder transitions and metallic collapse. Void formation at these damage thresholds promotes the accumulation of wrong bonds and homopolar configurations, whereas non-void cascades preferentially maintain ABAB stacking motifs and exhibit higher structural resilience. This contrast is consistently supported by short- and medium-range order metrics, as well as by our newly introduced Milliken Ring Population (MRP) analysis. At the electronic damage dose (∼3 × 10⁵ MeV/g), GST exhibits rapid band-gap collapse, a sharp rise in the imaginary dielectric function, and a pronounced decline in the real dielectric function, most severe for Te PKAs. These findings establish a clear mechanistic foundation for irradiation-induced disorder in GST and offer methodological insights that can guide the design of radiation-resilient phase-change memory technologies for aerospace applications.