Plasmonically-enhanced nanowire platform – a new detector architecture to boost remote sensing and thermal imaging?

Technological advances in the optical sensing field have led to the development of semiconductor photodetectors. Particularly, there is a significant demand from applications in remote sensing and thermal imaging at infrared over 2µm. In the optical spectrum, this wavelength regime is located at short-wave infrared and mid-wave infrared. Currently, development of high-performance photodetectors with room-temperature operation and high-detectivity is highly desirable. Unfortunately, the detectors operating over 2µm normally require additional cooling due to extremely high thermal noise, which adds to the complexity of the system design, e.g. attaching liquid nitrogen container or thermoelectric cooler to detector arrays. To solve this problem, researchers from University of California at Los Angeles and Cardiff University have recently delivered a plasmonically-enhanced nanowire infrared photodetection architecture, a promising candidate to achieve high-detectivity at room temperature by lowering thermal noise. The work was recently published in Nanotechnology.

“We utilized InAsSb-InP nanowire photodetector arrays to suppress thermal noise. The material volume of nanowire arrays is very small, much less than that used in detector pixels in those commercialized detectors,” says Dr. Dingkun Ren, the lead author. “The thermal noise is positively proportional to the volume of the absorber. Thus, the idea behind our research is to use nanostructures to miniaturize the absorption regions. Our calculation shows the noise can be reduced by over 3 orders, or 1,000 times, and the detector sensitivity can be improved by at least one order, or 10 times. Additionally, the plasmonic structure in our device can lead to a high optical absorption as well.”

Ren and his co-workers commenced their study by a detailed cross-examination of room temperature photodetection. They developed a 3D photoresponse model entailing framework-based nanowires and p-n heterojunctions. In the paper, they claimed the peak photodetector detectivity can reach greater than 3.5 x 10¹⁰cm Hz^1/2 W^-1. This was attributed to the reduction of the photo-absorber volume and elimination of the minority carrier diffusion by p-n heterojunctions. They also examined the influence of the nanowire material properties, such as carrier lifetime, doping level and carrier mobility–on the detectivity of the nanowire photodetectors. In addition, they demonstrated the multispectral capability by tuning the plasmonic peaks with different geometries of nanowire arrays.

“Our device platform can operate within the wavelength region of 2.0-3.5µm. We can further push the detection limit over 4µm and even toward long-wave infrared,” Ren comments. “Our work elucidates on the key considerations in enhancing the detectivity of photodetectors using nanostructured device architecture.”

Altogether, the study has provided vital information that can advance the design and optimization of high-performance photodetectors for numerous applications in remote sensing and thermal imaging at short- and mid-wave infrared. “We hope our research can support the industrial sectors in infrared photodetection,” says Ren.