High-power photodiodes

Ever since the trend of replacing conventional coaxial cables with optical fibers to transmit microwave signals, there have been a tremendous number of applications of microwaves in both military and civilian areas. The optical Radio-Frequency (RF) link requires high-speed high-power transceiver/receiver modules to realize high capacity and reliable data transmission. As the core element in the receiver end, photodiode is responsible for converting light back into electrical form with minimum signal distortion and crosstalk.;Power handling capability is an essential figure of merit for photodiodes that are utilized in analog optical links in order to minimize the loss of the analog optical link. In this dissertation the saturation mechanisms in modified uni-traveling-carrier (MUTC) photodiodes are investigated, and novel epitaxial structures are designed to improve the saturation current. Two MUTC structures based back-side illuminated photodiodes are fabricated, and the role of cliff layer is confirmed in the saturation current measurement. MUTC based balanced photodetector was developed to achieve high power with high CMRR of 38 dB up to 15 GHz. The influence of thermal stress on the photodiodes is also investigated with thermal imaging technique and simulated. And then a self-aligned flip-chip bonding technique is developed to improve heat dissipation of the photodiodes. A flip-chip bonded MUTC photodiode on AlN substrate shows a record high output RF power of 0.75 W at 15-GHz bandwidth.;With the enhanced saturation current and power capacity introduced by the MUTC structure, a MUTC based V-band optoelectronic mixer is demonstrated to achieve a record high up-converted power of 0.7 dBm at 59.5 GHz with a low conversion loss of −3.2 dB.;To investigate the possibility of deploying surface texture technique to realize broadband absorption, a Si-based surface-textured photodiode is demonstrated. The external quantum efficiency achieved a broadband response with efficiency > 70% from 430 nm to 890 nm and high UV quantum efficiency of 62 % at 245 nm.