GaSb-Based p-i-n Photodiodes with Partially Depleted Absorbers for High-Speed and High-Power Performance at 2.5-μm Wavelength

We first demonstrate a novel high-speed and high-power p-i-n photodiode with a cutoff wavelength at ∼ 2.5 μm. This device is composed of a partially depleted p-type Ga_0.8In_0.2As_0.16Sb_0.84 photo-absorption layer grown on GaSb substrate in order to enhance its speed and saturation power performance. With proper passivation processes, a low dark current (∼0.7 μA) and wide (6 GHz) optical-to-electrical (O-E) bandwidth can be simultaneously achieved with a miniaturized size of active mesa diameter (∼8 μm) under 1.55-μm optical wavelength excitation. The electron/hole drift-velocity and electron mobility across the Ga_0.8In_0.2As_0.16Sb_0.84 active layer can further be estimated based on the extracted internal response time and device modeling technique. Using the heterodyne-beating setup at 1.55-μm wavelength, the demonstrated device shows a saturation current at ∼3.6 mA (at 6-GHz operating frequency), which is mainly limited by the space-charge (electron/hole) induced screening effect at the depleted absorption region.