  Chalcogenide phase-change materials (PCMs) are regarded as the leading
candidate for storage-class non-volatile memory and neuro-inspired computing.
Recently, using the $TiTe_2$/$Sb_2Te_3$ material combination, a new framework -
phase-change heterostructure (PCH), has been developed and proved to
effectively suppress the noise and drift in electrical resistance upon memory
programming, largely reducing the inter-device variability. However, the
atomic-scale structural and chemical nature of PCH remains to be fully
understood. In this work, we carry out thorough ab initio simulations to assess
the bonding characteristics of the PCH. We show that the $TiTe_2$ crystalline
nanolayers do not chemically interact with the surrounding $Sb_2Te_3$, and are
stabilized by strong covalent and electrostatic Ti-Te interactions, which
create a prohibitively high barrier for atomic migrations along the pulsing
direction. We also find significant contrast in computed dielectric functions
in the PCH, suggesting possible optical applications of this class of devices.
With the more confined space and therefore constrained phase transition
compared to traditional PCM devices, the recently introduced class of PCH-based
devices may lead to improvements in phase-change photonic and optoelectronic
applications with much lower stochasticity during programming.
