Gigahertz InGaAs-based vertical Schottky diode optical detectors by substrate removal

In this paper, we present high-performance InGaAs vertical Schottky diode optical detectors and document design criteria and fabrication processes. The photodiodes are n-type and have an asymmetric contact structure with a rectifying anode and ohmic cathode. The vertical structure is achieved through InP substrate removal which exposes the back surface of the epitaxial layers. Ohmic contact is made to the exposed back surface. High-quality Schottky diodes with φ_Bn≈0.85 V are reproducibly achieved through an etching pretreatment, resulting in dark currents below 10 pA/μm² . Substrate removal and mesa definition result in low parasitic capacitance without the need of air bridges and allow accurate fiber-to-detector alignment. Responsivities greater than 0.7 A/W are obtained when a transparent conductor is used as the ohmic contact. RC-limited bandwidths as high as 19 GHz are measured for 20×20 μm² devices