High-Speed Mid-Wave Infrared Uni-Traveling Carrier Photodetector for Free-Space Optical Communication

Despite significant progress, high-speed mid-wave infrared (MWIR) photodetectors (PDs) still struggle to simultaneously achieve high bandwidth, high responsivity, and low dark current, limiting their suitability for practical applications. Here, we demonstrate an MWIR InAs/InAsSb type-II superlattice (T2SL) uni-traveling carrier (UTC) photodetector designed for high-speed operation. At room temperature and under a bias of $-$1 V, the device exhibits a dark current density of 2.75 A/cm $^{2}$, a peak responsivity of $\sim$0.8 A/W at 4 $\mu$ m, and a 3-dB bandwidth of 3.76 GHz. Increasing the bias to $-$2.5 V extends the 3-dB bandwidth to 7.21 GHz. Comprehensive modeling is performed to quantitatively evaluate the device performance. As aparse proof of concept, the packaged detector was integrated into a free-space optical communication (FSOC) system, achieving a data rate of 6 Gbaud with a clearly open non-return-to-zero (NRZ) eye diagram.