Model experiments on growth modes and interface electronics of CuInS_2: Ultrathin epitaxial films on GaAs(100) substrates

Abstract

The heterojunction formation between GaAs(100) and CuInS_2 is investigated using ultraviolet photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS), and low energy electron diffraction (LEED). Thin layers of CuInS_2 films were deposited in a step-by-step process on wet chemically pre-treated GaAs(100) surfaces by molecular beam epitaxy (MBE) with a total upper thickness limit of the films of 60 nm. The film growth starts from a sulfur-rich GaAs(100) surface. XPS core level analysis of the substrate and film reveals initially a transitory growth regime with the formation of a Ga containing chalcopyrite phase. With increasing film thickness, a change in stoichiometry from Cu-poor to Cu-rich composition is observed. The evaluation of the LEED data shows the occurrence of a recrystallization process where the film orientation follows that of the substrate with the epitaxial relation GaAs{100}||CuInS_2{001}. On the completed junction with a CuInS_2 film thickness of 60 nm, the band discontinuities of the GaAs(100)/CuInS_2 structure measured with XPS and UPS were determined as ΔE_V = 0.1 ± 0.1 eV and ΔE_C = 0.0 ± 0.1 eV, thus showing a type II band alignment.