Method for layer separation of GaAs Solar Cell Grown on a Porous Germanium using a Stress-Inducing Layer

Current III-V triple-junction solar cells rely on germanium (Ge) substrates, of which only a thin active layer is required. The remainder, comprising over 80% of the cell’s weight and 30% of its cost, is discarded. To improve this, we present a method to recover and reuse Ge substrates via a novel stress-based detachment process. Our approach is based on epitaxial growth on a porous Ge weak layer, formed using a bipolar electrochemical etching process. This process produces a weak layer that enables the growth of epitaxial heterostructure while maintaining substrate integrity. A stress-inducing nickel (Ni) layer, deposited via electroplating, provides the necessary strain energy for layer separation without damaging the membrane. This method systematically addresses challenges related to substrate detachment, such as avoiding membrane cracking and ensuring compatibility with standard microfabrication processes. Results demonstrate that membrane detachment is achievable with controlled Ni deposition parameters, tailored for varying weak layer morphologies. SEM analysis confirms successful pillar breakage, and comparative studies validate the effectiveness of the stress layer in preventing cracks. After detachment, the Ge substrate can be reconditioned for subsequent use, significantly reducing material waste and costs. This work provides a scalable solution for high-yield substrate detachment in III-V solar cells and other optoelectronics devices.