Dual-barrier detector design improves chances of gravitational wave detection

The two-micrometer wavelength band sees significant use in gravitational wave detection and astronomical observation. However, the signals in current detectors are weak and background noise interference (or “dark current”) is high. Li et al. designed a detector that suppresses unwanted signals in the two-micrometer wavelength band by band engineering antimony-based, Type II superlattices.

In their antimony-based device, the team used a dual-barrier structure that separated absorption and depletion regions in detected photocurrents and suppressed four main contributors to background noise: diffusion, recombination, tunneling, and surface dark currents. Their experiments showed that a detector with a diameter of 500 micrometers and a bias of -0.5 Volts resulted in lower dark currents than those described in other papers, with a dark-current density of 2.5 x 10⁻⁶ A/cm² at operating temperatures.

“In Type II antimony-based superlattices, band engineering results in minimal changes to the valence band offset, while the conduction band offset can be tailored to create various barrier structures,” author Mingming Li said. “The dual-barrier structure used in this study effectively blocks electron transport while allowing hole transport to remain unaffected.”

That dual-barrier region was a key addition to the authors’ device, which otherwise utilized a more traditional type-II superlattice structure. To understand the mechanisms behind their device, they calculated key physical quantities of the absorption region, including the probability distributions of electrons in space, and quantitatively characterized the influence of different dark-current mechanisms on the bulk dark current in their detector.

Their next steps include improving the device sensitivity by tuning their detector’s doping profile and superlattice composition.

Source: “Low dark current Sb-based short-wavelength infrared photodetector,” by Mingming Li, Yifan Cheng, Xiangyu Zhang, Ye Zhang, Dongwei Jiang, Zhigang Song, and Wanhua Zheng, AIP Advances (2024). The article can be accessed at https://doi.org/10.1063/5.0207138 .