Tuning the Electronic Band Structure of Copper Selenide Cu₂Se Thin Films Grown via Molecular Beam Epitaxy

Cu₂Se has long been known to be an excellent thermoelectric material whose electronic band structure that is tunable by introducing copper vacancies into the crystal structure. More recently, this compound has been predicted to host topologically-protected surface states. In this work, we will present our successful epitaxial growths of Cu_2-xSe thin films via molecular beam epitaxy (MBE). Using reflection high energy electron diffraction (RHEED) and x-ray diffraction (XRD) measurements, we will show how we are able to quantify the copper concentration by analyzing the subtle shifts in our observed XRD spectra corresponding to small changes in the lattice spacing due to these copper vacancies and how these vacancies influence electronic transport in the film. In this manner we will demonstrate how we are able to tune the copper vacancies and electronic band structure by precise control of the crystal’s growth parameters.