Development of Infrared Sensor Capable of Detecting Wavelengths 1.55–3μm at Room Temperature: Expected to Expand into Home, Medical, Environmental, and Food Industries

### Key Points of the Research

- Developed a compact sensor capable of detecting infrared light up to the 3μm band at room temperature—a feat previously difficult to achieve—by combining electrodes that offer both high transparency and conductivity in the near-to-mid-infrared range with semiconductor materials that efficiently absorb infrared rays. - Succeeded in the high-quality crystal growth of a p-type GeSn layer containing 13.6% Tin (Sn), exceeding the equilibrium solid solubility limit on a Germanium (Ge) substrate, thereby achieving sensitivity in the 3μm wavelength band. - This compact sensor (photodiode) can detect infrared light from telecommunication wavelengths (around 1.55μm) to near 3μm with a single element. It is expected to be applied in a wide range of fields, including gas detection, environmental monitoring, healthcare (breath analysis), quality control for food and pharmaceuticals, industrial process monitoring, infrared imaging, and spectroscopic sensing for security.

### Research Overview A joint research group led by Professor Osamu Nakatsuka and Assistant Professor Shigehisa Shibayama of the Graduate School of Engineering at Nagoya University, along with Dr. Tomo Tanaka of NEC Corporation, and Dr. Tatsuo Maeda and Dr. Rahmat Hadi Saputro of the Advanced Semiconductor Research Center at the National Institute of Advanced Industrial Science and Technology (AIST), has developed a new Germanium-Tin (GeSn)/Germanium (Ge) junction infrared sensor compatible with Silicon integrated circuit process technology.

The prototype sensor achieved detection up to the 3μm band at room temperature by combining iTCO (infrared-transparent conductive oxide) electrodes with GeSn material. Utilizing a low-temperature MBE (Molecular Beam Epitaxy) method developed at Nagoya University, they achieved high-quality epitaxial growth of a p-type GeSn mixed crystal layer with a high Sn composition of 13.6%. Evaluations of the iTCO/p-type GeSn/n-type Ge photodiode fabricated at AIST demonstrated that a single element can cover wavelengths from 1.55μm to 3μm.

The results will be presented at the Conference on Lasers and Electro-Optics (CLEO) on May 20, 2026.

### Background and Content Light near 3μm, known as 'mid-infrared,' is in a region where molecular characteristics (molecular fingerprints) can be identified, such as greenhouse gases like methane, molecules in human breath, and differences in food and medicine quality. Methane (CH4), for instance, has strong absorption at 3.3μm, making it vital for leak monitoring.

Existing high-sensitivity sensors in this range require cooling, making them bulky and expensive. Standard InGaAs sensors have a main range up to ~1.67μm, with advanced versions capping at ~2.6μm. This left a gap in the 2.6–3.3μm range that needed a compact, low-cost solution operable at room temperature.

The newly developed device has two major advantages: 1. It can operate at room temperature. 2. It can be manufactured using standard semiconductor processes, making it suitable for mass production.

These features establish the foundation for the widespread adoption of mid-infrared sensing in daily life scenarios, such as in homes, healthcare, environmental monitoring, and the food industry.