NAVAL RESEARCH LAB WASHINGTON DC WASHINGTON DC United States
We use a drift-diffusion model to study frequency dependent harmonic powers in a modified unitraveling- carrier MUTC photodetector. The model includes external loading, incomplete ionization, the Franz-Keldysh effect, and history-dependent impact ionization. It also takes into account heat flow in the device. In three-tone measurements, the bias voltage at which a null occurs bias null in the second order intermodulation distortion IMD2 is different for the sum frequency and difference frequency. We obtained agreement with the experimental results. The bias null that appears in the IMD2 is due to the Franz-Keldysh effect. The bias null depends on the electric field in the intrinsic region, and the difference of the bias null for the sum frequency and difference frequency are due to the displacement current in the intrinsic region. When the frequency is large, the displacement current is large and has a large effect on the harmonic powers. We also found that the bias null depends on the recombination rate in the p-absorption region because the electric field decreases in the intrinsic region when the recombination rate in the p-region decreases.