High-Quality-Factor AlGaAs-On-Sapphire Microring Resonators

We realize an AlGaAs-on-sapphire platform through a Al<formula><tex>$_2$</tex></formula>O<formula><tex>$_3$</tex></formula>-assisted direct wafer bonding and substrate removal processes. The direct wafer bonding process is optimized concerning the intermediate layer deposition and annealing temperature to obtain a high bonding strength between the AlGaAs and sapphire wafers. High quality-factor (Q) microring resonators are fabricated using electron-beam lithography in which the charging effect is mitigated by applying an thin aluminum layer and a smooth pattern sidewall definition is obtained using a multi-pass (exposure) process. We achieve an intrinsic Q of up to <formula><tex>$\sim$</tex></formula>460,000, which is the highest Q for AlGaAs microring resonators. Taking advantage of such high Q resonators, we demonstrate an ultra-efficient nonlinear four-wave mixing process in this platform and obtain a conversion efficiency of -19.8 dB with continuous-wave pumping at a power level of 380 &#x03BC;W. We also investigate the thermal resonance shift of microring resonators with different substrate layouts and observe a superior thermal stability for devices in the AlGaAs-on-sapphire platform. The realization of the AlGaAs-on-sapphire platform also opens new prospects for AlGaAs devices in nonlinear applications in the mid-infrared wavelength range.