Phase-change
materials are of great interest for low-power high-throughput
storage devices in next-generation neuromorphic computing technologies.
Their operation is based on the contrasting properties of their amorphous
and crystalline phases, which can be switched on the nanosecond time
scale. Among the archetypal phase change materials based on Ge–Sb–Te
alloys, Sb2Te3 displays a fast and energy-efficient
crystallization–amorphization cycle due to its growth-dominated
crystallization and low melting point. This growth-dominated crystallization
contrasts with the nucleation-dominated crystallization of Ge2Sb2Te5. Here, we show that the energy
required for and the time associated with the amorphization process
can be further reduced by using a photoexcitation-based nonthermal
path. We employ nonadiabatic quantum molecular dynamics simulations
to investigate the time evolution of Sb2Te3 with
2.6, 5.2, 7.5, 10.3, and 12.5% photoexcited valence electron–hole
carriers. Results reveal that the degree of amorphization increases
with excitation, saturating at 10.3% excitation. The rapid amorphization
originates from an instantaneous charge transfer from Te-p orbitals to Sb-p orbitals upon photoexcitation.
Subsequent evolution of the excited state, within the picosecond time
scale, indicates an Sb–Te bonding to antibonding transition.
Concurrently, Sb–Sb and Te–Te antibonding decreases,
leading to formation of wrong bonds. For photoexcitation of 7.5% valence
electrons or larger, the electronic changes destabilize the crystal
structure, leading to large atomic diffusion and irreversible loss
of long-range order. These results highlight an ultrafast energy-efficient
amorphization pathway that could be used to enhance the performance
of phase change material-based optoelectronic devices.