Gallium Phosphide-on-Silicon Dioxide Photonic Devices
The development of integrated photonic circuits utilizing gallium phosphide requires a robust, scalable process for fabrication of GaP-on-insulator devices. Here, we present the first GaP photonic devices on SiO2. The process exploits direct wafer bonding of a GaP/AlxGa1-x P/GaP heterostructure onto a SiO2-on-Si wafer followed by the removal of the GaP substrate and the AlxGa1-xP stop layer. Photonic devices such as grating couplers, waveguides, and ring resonators are patterned by inductively coupled-plasma reactive-ion etching in the top GaP device layer. The peak coupling efficiency of the fabricated grating couplers is as high as -4.8 dB. Optical quality factors of 20 000 as well as second- and third-harmonic generation are observed with the ring resonators. Because the large bandgap of GaP provides for low two-photon absorption at telecommunication wavelengths, the high-yield fabrication of GaP-on-insulator photonic devices enabled by this work is especially interesting for applications in nanophotonics, where high quality factors or low mode volumes can produce high electric field intensities. The large bandgap also enables integrated photonic devices operating at visible wavelengths.