Fabrication of tunable InP/air-gap Fabry-Perot cavities by selective etching of InGaAs sacrificial layers

We report the fabrication of InP/air-gap Fabry-Perot resonant cavities with an improved tunability characteristic achieved through the micromachining of more flexible suspended InP beams. The micromechanical structures are el ectrostatically actuated. A tuning range of 55 nm is demonstrated for an ac tuation voltage of 12 V. The low leakage current, of less than 10 mu A for a bias of up to 30 V, provides a low actuation power. The tunable air-gap c avities are fabricated by selective wet etching of InGaAs sacrificial layer s. An FeCl3 based etchant is used to completely remove the InGaAs material without affecting the thickness of the InP layer. The anisotropy of the etc h rate of InGaAs was also investigated and exploited in the micromachining process.