Epitaxtial lift-off for freestanding InGaN/GaN membranes and vertical blue light-emitting-diodes†
Growth substrates of InGaN/GaN light-emitting-diodes (LEDs) greatly restrict their further applications owing to the residual internal stress and polarization. Herein, we report the preparation of freestanding InGaN/GaN membranes and vertical blue LEDs through an electrochemical (EC) etching process. The maximum size of the obtained freestanding membranes are up to the millimeter scale with no obvious cracks existing. By collecting photoluminescence (PL) and Raman scattering spectra of the InGaN/GaN epitaxial structure and the transferred freestanding membranes, it is confirmed that the residual compressive strain between the epitaxial structure and growth substrate is effectively released. The corresponding electroluminescence (EL) measurement of the transferred membranes LEDs was conducted by using a probing test with a spectrograph. The EL spectra exhibiting three stable light emitting peaks and the emission intensity increase with the injected currents. This research proposes a low-cost method to fabricate freestanding InGaN/GaN membranes and high performance vertical blue LEDs.