Atomic‐Scale Mechanisms of Anisotropic Thermal Decomposition in GeSn Alloys With Stepwise Pinning

Abstract

Thermal decomposition of GeSn layers detrimentally affects device performance, while the governing mechanisms remain shrouded by the presence of SiO 2 passivation. In this work, we elucidate the atomic‐scale decomposition of GeSn during thermal degradation using in situ heating TEM. Two divergent decomposition modalities are identified: a Laminar Receding mode in defect‐free regions, characterized by uniform, layer‐by‐layer interfacial recession; and a Stepwise Pinning mode in the presence of stacking faults, where the decomposition boundary is intermittently arrested by defects and advances discretely upon overcoming local energetic barriers. First‐principles calculations reveal a preferred decomposition boundary along [11] crystallographic orientation as the kinetically preferred pathway due to its minimal energy barrier, while the [001] orientation provides thermodynamic stability with an exceptionally low formation energy of 0.08 eV/Å. The competitive interplay between these two orientations dictates the characteristic stepped boundary morphology, which is energetically optimized at a step length of approximately two atomic spacings. Furthermore, we demonstrate that surface defects impose a substantial energetic penalty on atom removal, providing an atomistic basis for the observed pinning effect. By correlating defect‐mediated anisotropic decomposition with its crystallographic dependence, this study establishes a foundational physical framework for enhancing the thermal stability of GeSn heterostructures.