Epitaxial Growth of Sr₃Al₂O₆ by Pulsed Laser Deposition as a Water-Soluble Sacrificial Layer for GaAs Deposition

Despite the record high efficiency for GaAs solar cells, its terrestrial application is limited due to both the particularly high costs related to the required single crystal substrates and the epitaxial growth. A water-soluble lift off layer could reduce costs by avoiding the need for toxic etchants, substrate re-polishing and expensive process steps.
Sr₃Al₂O₆ (SAO) is a water soluble, cubic oxide with lattice constant 15.84Å. This is close to (2√2)a_GaAs, giving a close lattice match after 45° lattice rotation. We investigated the epitaxial growth of high structural quality SAO on single crystal SrTiO₃ (STO) substrates by pulsed laser deposition, and the feasibility of subsequently growing GaAs epitaxially on top of it. We identified that the SAO film quality is strongly dependent on the growth temperature and O₂ partial pressure. An STO capping layer was grown on the SAO to protect from moisture induced degradation. XRD spectra for the films with optimized deposition parameters showed epitaxial SAO aligned to the STO (100) substrate. TEM analysis revealed that the grown SAO films are epitaxially crystalline throughout the thickness. The epitaxial growth of the STO capping layer is a qualitative indication for the high quality of the SAO surface.