Limitations to Power Conversion Efficiency of InP Based Uni-traveling-carrier Photodiodes Due to Space Charge Resistance

The limiting mechanism for power conversion efficiency of uni-traveling-carrier photodiodes (UTC-PDs) for generating microwave signals is discussed. Experimental results are shown for a waveguide UTC-PD with a bandwidth of 50 GHz. The space charge resistance of this device is extracted and shown to limit the maximum power conversion efficiency to around 4%.