Photocurrent Saturation and Thermal Breakdown Mechanism in Modified Uni-Traveling-Carrier Photodetectors

In this paper, we used an optimized mobility model which contains the effects of ionized impurity scattering, lattice vibration scattering, velocity saturation under high-electric-field and the heat transfer module to simulate the mechanism of saturation photocurrent of modified Uni-Traveling-Carrier photodetectors. It is shown that the electron drift speed is hindered by charge shielding effect mainly due to the accumulation of electrons at the heterojunction between the absorption and the collection layer. Accordingly, an optimized modified Uni-Traveling-Carrier photodetector was proposed in which electrons are kept at a high drift speed resulting in improved device saturation characteristics. Finally, we succeeded in creating a mesa-type Uni-Traveling-Carrier photodetector with a 9 mu m diameter and a saturation current more than 40 mA at 3 V bias with the bandwidth of 40 GHz.