Ultracompact Multilayer Fabry–Perot Filter Deposited in a Micropit

We fabricate a multilayer Fabry-Perot filter (FPF) on a GaN-on-silicon platform. Being significantly different from conventional thin film FPFs formed on smooth flat surfaces, this FPF is deposited in a micropit, and takes a suspended GaN membrane as its carrier, which makes the whole structure ultracompact. The reflection spectra of the FPF are characterized by using an angle-resolved microreflection measurement system. The experimental results show that its spectra generally have a considerable blue shift in comparison with that of its conventional counterpart formed on the smooth flat surface; moreover, its thickness is not uniform but varies along its lateral dimension, suggesting that its spectral properties are highly localized. Resonable explanations are provided to illuminate its particular spectral phenomena. Finally, the localized thicknesses of the thin films composing the FPF are obtained by fitting the measured reflection curves with the simulated ones. This kind of FPF may be integrated monolithically into a batch of suspended membrane devices to endow them with the desired wavelength selectivity.