Enhancement in speed and responsivity of uni-traveling carrier photodiodes with GaAs_0.5Sb_0.5/In_0.53Ga_0.47As type-II hybrid absorbers

We demonstrate a top-illuminated high-speed uni-traveling carrier photodiode (UTC-PD) with a novel design in the p-type absorber, which can effectively shorten the photon absorption depth at telecommunication wavelengths (1.31∼1.55 μm) and further enhance the bandwidth-efficiency product of UTC-PD. In our proposed new UTC-PD structure, the p-type In_0.53Ga_0.47As absorption layer is replaced by the type-II GaAs_0.5Sb_0.5 (p)/In_0.53Ga_0.47As (i) hybrid absorber. Due to the narrowing of the bandgap and enhancement of the photo-absorption process at the type-II interface between the GaAs_0.5Sb_0.5 and In_0.53Ga_0.47As layers, our device shows an over 16.7% improvement in the responsivity compared with that of UTC-PD with the same thickness of pure In_0.53Ga_0.47As absorber (0.7 μm) and a zero optical coupling loss. Our demonstrated device with a simple top-illuminated structure offers a large active mesa (25 μm), a wide optical-to-electrical (O-E) bandwidth (33 GHz), a high responsivity (0.7 A/W), and a high saturation current (>5 mA) under 1.31 μm optical wavelength. These promising results suggest that our proposed PD structure can fundamentally overcome the trade-off among bandwidth, efficiency, and device active diameter of high-speed PDs.