Wafer bonding and epitaxial transfer of GaSb-based epitaxy to GaAs for monolithic interconnection of thermophotovoltaic devices
GaInAsSb/AlGaAsSb/InAsSb/GaSb epitaxial layers were bonded to semi-insulating (SI) GaAs handle wafers with SiOx/Ti/Au as the adhesion layer for monolithic interconnection of thermophotovolatic (TPV) devices. Epitaxial transfer was completed by removal of the GaSb substrate, GaSb buffer, and InAsSb etch-stop layer by selective chemical etching. The SiOx/Ti/Au provides not only electrical isolation, but also high reflectivity and is used as an internal backsurface reflector (BSR). Characterization of wafer-bonded (WB) epitaxy by high-resolution x-ray diffraction (HRXRD) and time-decay photoluminescence (PL) indicates minimal residual stress and enhancement in optical quality. The 0.54-eV GaInAsSb cells were fabricated and monolithically interconnected in series. A ten-junction device exhibited linear voltage building with an opencircuit voltage of 1.8 V.