InSe thin film properties and growth on GaAs(111)B by molecular beam epitaxy

This work presents the growth of InSe thin films by molecular beam epitaxy on GaAs(111)B substrates. Large-scale structural characterization by X-ray diffraction, and Raman spectroscopy revealed that the films were predominantly gamma-InSe phase. Microstructure analysis confirmed this result but demonstrated that a mixture of different polytypes was present in the films. In addition, a novel polymorph of InSe was found in the films by transmission electron microscopy. Density functional theory calculated the formation energies for different InSe polytypes, i.e., layer stacking sequences and stacking faults as well as polymorphs to be relatively small compared to the non-equilibrium growth conditions employed, highlighting the likelihood of observed polymorph/polytype formation during growth. Although theoretical calculations arrived at comparable formation energies and band gaps for different polytypes and polymorphs, their relative band alignment was found to be sizeable. Consequently, the electronic disorder introduced by the mixture of polytypes and polymorphs was reflected in the electronic transport properties of the film that showed hopping-like characteristics.