Wafer bonding and its application on compliant universal (CU) substrates

We have recently found a novel and significant application for the wafer bonding technology. We demonstrated that by bonding an ultra thin layer of semiconductor to a bulk crystal with a rotational angle along their surface normal, this new structure can achieve interesting behaviors as a compliant substrate. When heteroepitaxial layers are grown on such twist-bonded substrates, the bonded thin layer is plastically deformed to relax the strain before threading dislocations are nucleated in the heteroepitaxial layer. This is a new and energetically more favorable way for lattice strain relaxation and is unique to the twist-bonded structure. We found that this concept can be applied to many semiconductors such as GaAs and Si to form compliant substrates where heteroepitaxy of exceedingly large lattice mismatch (e.g. 15%) can be grown without defects. This implies that twist-bonded compliant substrates may, to a large extent, function as a universal substrate for growth of high quality materials of nearly any lattice constant