High-Responsivity Unitraveling Carrier–Type Photodetector Using Avalanche InAlAs as a Collector at a High-Frequency Range

In this study, we proposed a novel design for fabricating a unitraveling carrier–type photodetector using In0.52Al0.48As as the collector material. The proposed InAlAs photodetector is based on the structure of a conventional unitraveling carrier–type photodetector with an InP collector and is considered to transplant the concept of an avalanche photodetector using the avalanche material InAlAs. Based on the high responsivity of the avalanche photodetector at a high-frequency range, a unitraveling carrier–type photodetector with an avalanche InAlAs collector (10- $\mu \text{m}$ junction diameter) was fabricated. The measured I–V characteristics showed that the proposed photodetector can demonstrate the avalanche effect. The measured 3-dB bandwidths were 43, 26, and 19 GHz at multiplication gains of 1, 2, and 3.5, respectively. Furthermore, the multiplied responsivity (defined as the product of gain and responsivity under the unit gain condition) was >0.6 A/W under the low gain condition (0.187 A/W under the unit gain condition). Furthermore, estimations for the 3-dB bandwidth were discussed, and the experimental results were found to be consistent with the simulation results. The improvements in the proposed photodetector with a 5- $\mu \text{m}$ junction diameter were predicted. We expect the 3-dB bandwidth and responsivity of the proposed photodetector to reach 100 GHz and 0.7 A/W, respectively, with a low multiplication gain.