Realizing the Heteromorphic Superlattice: Repeated Heterolayers of Amorphous Insulator and Polycrystalline...

An unconventional "heteromorphic" superlattice (HSL) is realized, comprised of repeated layers of different materials with differing morphologies: semiconducting pc-In₂ O₃ layers interleaved with insulating a-MoO₃ layers. Originally proposed by Tsu in 1989, yet never fully realized, the high quality of the HSL heterostructure demonstrated here validates the intuition of Tsu, whereby the flexibility of the bond angle in the amorphous phase and the passivation effect of the oxide at interfacial bonds serve to create smooth, high-mobility interfaces. The alternating amorphous layers prevent strain accumulation in the polycrystalline layers while suppressing defect propagation across the HSL. For the HSL with 7:7 nm layer thickness, the observed electron mobility of 71 cm²  Vs^-1 , matches that of the highest quality In₂ O₃ thin films. The atomic structure and electronic properties of crystalline In₂ O₃ /amorphous MoO₃ interfaces are verified using ab-initio molecular dynamics simulations and hybrid functional calculations. This work generalizes the superlattice concept to an entirely new paradigm of morphological combinations.