Group III selenides: Controlling dimensionality, structure, and properties through defects and heteroepitaxial growth

Abstract

This Review describes behaviors and mechanisms governing heteroepitaxial nucleation and growth of group III (Al, Ga, and In)–selenium (Se) based semiconductors by molecular beam epitaxy and the properties of the resultant nanoscale films. With nine bonding electrons per AIII–BVI pair, these chalcogenide semiconductors crystallize in a variety of locally tetrahedral bulk structures that incorporate intrinsic vacancies (atom-sized voids) lined with doubly occupied lone-pair orbitals, including layered, defected zinc blende and defected wurtzite structures. During heteroepitaxial growth, the choice of how the vacancies order and which phase results, as well as interface reactions, intermixing, surface passivation, and film morphology, are controlled by electron counting, substrate symmetry, and size mismatch. Nucleation and growth of AlxSey, GaxSey, and InxSey compounds on Si and GaAs, including initial reactions, layer nucleation, symmetry, crystal structure, defects, dimensionality, and stoichiometry, were studied with a combination of techniques, including photoelectron spectroscopy, x-ray photoelectron diffraction, scanning tunneling microscopy, x-ray absorption spectroscopy, and low energy electron diffraction. The unique crystal structure of Ga2Se3 was also investigated as a novel platform for doping with transition metals to create a dilute magnetic semiconductor: Cr:Ga2Se3 is ferromagnetic at room temperature, while Mn:Ga2Se3 results in the precipitation of MnSe. The present study provides new insight into growing interest in variable dimensional materials, using group III selenides as prototypes, to address the basic physical chemistry governing the heteroepitaxy of dissimilar materials.