Flexible GaAs Solar Cell Using Water-Soluble Sacrificial Layer for Epitaxial Lift-Off Process

Cost reduction of III- V semiconductor solar cells can be achieved by the epitaxial liftoff method which involves selective etching of a sacrificial layer and reusing the substrate. For GaAs epitaxial lift-off, lattice-matched AlAs is used as a sacrificial layer to separate the grown GaAs device from the GaAs wafer. Since selective etching of AlAs requires the use of concentrated hydrofluoric (HF) or hydrochloric acid (HCl) for an extended period of time, it could damage the GaAs wafer underneath. As a result, the wafer has to undergo expensive and intensive chemical mechanical polishing processes. In our work, we addressed this issue using a water-soluble lattice-matched sacrificial layer. Water-soluble alkaline earth compounds that possesses structural symmetry for epitaxial growth of zinc blende GaAs film were used. The best results were obtained with a 3-layer structure consisting of buffer layers of alkaline earth compounds tuned for lattice match with GaAs, sandwiching another water-soluble alkaline earth compound sacrificial layer. 2D X-ray Diffraction (XRD) measurement showed epitaxial growth of GaAs device film grown by metal-organic chemical vapor deposition on lattice-matched buffer film. Single junction solar cell devices have been fabricated with this architecture. Measurements at one sun showed minimal degradation in device performance before and after liftoff.