Spectrally tunable nanoscale silicon field-effect transistor detects 1.5 µm light

Conventional silicon (Si) photodetectors are used extensively in the UV, visible, and very near-IR (shorter than 1.2 µm) wavelengths; however, the 1.1 eV bandgap of Si precludes its use for detection of light at longer wavelengths (unless special tricks such as the addition of impurity sites are used).

Jul 1st, 2007

Conventional silicon (Si) photodetectors are used extensively in the UV, visible, and very near-IR (shorter than 1.2 µm) wavelengths; however, the 1.1 eV bandgap of Si precludes its use for detection of light at longer wavelengths (unless special tricks such as the addition of impurity sites are used). Now, researchers at NTT (Kanagawa, Japan), Shisuoka University (Hamamatsu, Japan), and Hokkaido University (Sapporo, Japan) are using nanoscale (a few hundred nanometers in size) metal-oxide-semiconductor field-effect-transistors (MOSFETS) to detect light at up to 1.5 µm wavelengths; the MOSFETs are compatible with large-scale Si integration.

Incoming IR light excites conduction-band electrons, some of which are injected into an electrically formed storage node; the electron signals are then detected by a gain cell that senses charge with single-electron resolution. Detection speed (on the order of seconds for a 3 µW/cm2 signal power) will be increased by enlarging and optimizing the structure. The MOSFET configuration allows electrical configuration of both sensitivity and the short-wavelength-pass value; the spectral-tuning ability will be useful in materials-analysis applications, say the researchers. Contact Katsuhiko Nishiguchi at knishi50@aecl.ntt.co.jp.

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