Epitaxial growth of detachable GaAs/Ge heterostructure on mesoporous Ge substrate for layer separation and substrate reuse

Currently, III-V multijunction solar cells holds the highest efficiency. However, they are expensive to produce and this prevents their large-scale use. For single GaAs solar cells, most of the total cost of the cell comes from the substrate. For III-V cells on Ge substrate, the thickness of the substrate is usually between 150 μm and 180 μm, whereas only 1 μm would be sufficient to maintain the performance of the cell. Moreover, 95% of the weight of the cell comes from the substrate which is a problem for the space domain. It is therefore necessary to find an economical and reliable approach for layer separation and reuse of Ge substrate. The approach proposed in this work shows the epitaxial growth of high-quality monocrystalline Germanium template on a 4-inch porous Ge substrate. The porous layer reconstruction leaves voided interface with nanometer scale pillars allowing defect free detachment of the epitaxial layer. Furthermore, the Ge epilayer demonstrates very low surface roughness, comparable to that of the epi-ready bulk Ge substrate with a preserved miscut angle suitable for III-V materials and solar cells heteroepitaxy. Accordingly, high crystal quality GaAs epilayer has been successfully demonstrated on the designed Ge template. Our finding paves the way to a reliable and cost-effective approach towards III-V/Ge multijunction solar cells detachment and substrate reuse that may constitute a technological breakthrough for both space and terrestrial PV applications.