A novel vacuum epitaxial lift-off (VELO) process for separation of hard GaAs substrate/carrier systems for a more green semiconductor LED production

This study reports on a novel vacuum epitaxial lift-off (VELO) process to reuse the GaAs substrates in light-emitting diode (LED) production. The method is based on an epitaxial lift-off technique, whose application is however limited to flexible wafers, as gaseous reaction products (e.g. AsH3) formed during the etching of AlAs with hydrofluoric acid are trapped within the wafer stack. In the developed VELO process, an applied vacuum of ∼5000Pa to the bonded wafer stack removes such detrimental reaction gases, allowing a separation of hard substrate/carrier systems. The VELO process is evaluated with a state-of-the-art thin-film light-emitting diode (TF-LED) phosphide-based epitaxial structure with a buried AlAs sacrificial layer and a simplified LED chip construction at 4-in. wafer level. Characterization of the so-processed LEDs using high-resolution x-ray diffraction, μ-photoluminescence and electrical testing reveal that the VELO TF-LEDs show a comparable performance like to released chips by using conventional grinding/polishing and etching of the GaAs substrate. As our VELO process is non-destructive to the substrate, the GaAs wafers can be reused, enabling lower costs for LED production and reduced toxic waste to establish a green semiconductor production.