InGaAs/InP Modified Uni-Travelling-Carrier Photodiode with a Cliff Layer

Due to the exceptional transmission property of optical fiber and the development of high-performance optoelectronic components, microwave photonic links have been used in many applications, including radio-over-fiber systems, optical beam forming and optical signal processing. To reduce insertion loss and enhance dynamic range in the microwave photonic links, it is crucial to implement high-power and high-linearity photodiodes. A promising candidate for this application is the uni-travelling-carrier photodiode (UTC-PD), which mitigates the space charge effect by using electrons as the only active carrier, thereby increasing the saturation current. In this work, an InGaAs/InP modified UTC-PD (MUTC-PD) is simulated, fabricated and characterized. The MUTC-PD electrostatics are first calculated using Synopsys Sentaurus TCAD, which provides insight and illustrates the device saturation mechanism (i.e. space charge effect). It is also found that a 'cliff layer' (e.g. lightly-doped InP layer inserted between the absorption and collection layer) helps suppress the space charge effect under high-illumination conditions and improves the device high power handling capability. An InGaAs/InP MUTC-PD epitaxial structure grown by MOCVD has also been processed into a frontside-illuminated photodiode by using optical lithography, wet and dry etch processes, dielectric planarization and metallization. The performance of these fabricated photodiodes were evaluated by measuring dark current, responsivity and bandwidth. Finally, the device's thermal behavior has been explored by way of MATLAB simulation. Since thermal heating limits the photodiode ultimate high-power performance, different thermal management strategies, like wafer transfer and heat sink, have been simulated and are compared.