Hetero-twinning in chemical epitaxy of PBS thin films on GaAs substrates

Twinning, i.e., inversion of atomic stacking sequence along a specific crystallographic axis, is a commonly occurring phenomenon in thin film growth. A very large number of reports have shown cases of conventional twinning within a single polycrystalline phase, where the plane of contact between the two twinned parts, called the composition plane, coincided with the twinning plane. Here we show for the first time twinning in heteroepitaxial monocrystalline PbS semiconductor thin films that are deposited from aqueous solutions under ambient conditions. The chemically deposited films show a distinct, well-defined "hetero-twin relationship with monocrystalline GaAs substrates of various orientations: (100), (111), and (110). Notably, the same twin relationship, with the (111) twin plane and [112̄] twinning direction was observed in all studied cases regardless of the composition plane.