Effects of Doping on Elastic Strain in Crystalline Ge-Sb-Te

Phase-change random access memory (PcRAM) faces significant challenges due to the inherent instability of amorphous Ge₂Sb₂Te₅ (GST). While doping has emerged as an effective method for amorphous stabilization, understanding the precise mechanisms of structural modification and their impact on material stability remains a critical challenge. This study provides a comprehensive investigation of elastic strain and stress in crystalline lattices induced by various dopants (C, N, and Al) through systematic measurements of film thickness changes during crystallization. Through detailed analysis of cross-sectional electron microscopy data and theoretical calculations, we reveal distinct behavior patterns between interstitial and substitutional dopants. Interstitial dopants (C and N) generate substantial elastic strain energy (~9 J/g) due to their smaller atomic radii (0.07-0.08 nm) and ability to occupy spaces between lattice sites. In contrast, substitutional dopants (Al) produce lower strain energy (~5 J/g) due to their similar atomic radius (0.14 nm) to host atoms. We demonstrate that N doping achieves higher elastic strain energy compared to C doping, attributed to its preferential formation of Ge-N bonds and resulting lattice distortions. The correlation between dopant properties, structural features, and induced strain energy provides quantitative insights for optimizing dopant selection. These findings establish a fundamental framework for understanding dopant-induced thermodynamic stabilization in GST materials, offering practical guidelines for enhancing the reliability and performance of next-generation PcRAM devices.