Photonics.com Printer Friendly View

1/2 ページ

Advertisementfrom photonics.com - 8/1/2007

http://www.photonics.com//content/spectra/2007/August/nanophotonics/88509.aspx

Infrared Detection at Room Temperature with Single-ElectronResolution
Lauren I. Rugani

Infrared signals with wavelengths longer than 1.2 µm often are excluded by the selectivity ofsilicon-based sensors. Sensors that use electron-hole pair generation require photons to haveenergy greater than the 1.1-eV bandgap energy of silicon, which only corresponds towavelengths in the visible region. Other methods require low-temperature operation.

A scanning electron microscopy
image shows (from right to left) theelectron reservoir, an energy
barrier formed by the lower gate
and a storage node, where injectedelectrons are read out as current.
The schematics show that noelectrons pass into the storage
node without infrared radiation.
More electrons are allowed overthe energy barrier, and thedetection current decreases as thewavelength of the infrared radiation
decreases.

A team from NTT Corp. in Atsugi,from Shizuoka University inHamamatsu and from Hokkaido
University in Sapporo, all in Japan,
has developed nanoscale silicon
metal-oxide semiconductor fieldeffect transistors to detect infrared
signals at room temperature. By
exciting electrons over anelectrically induced energy barrier,both the range of detectablewavelengths and the sensitivity ofthe device can be controlled.
The sensor works when an infrared
signal excites conduction-band electrons in a 25-nm-deep electron reservoir. A silicon-oninsulator channel measuring 40 × 400 nm is placed next to the reservoir to increase the numberof excited electrons. A poly-silicon lower gate then turns off the transistor and electrically forms
an energy barrier, creating a storage node on the other side. Electrons with energy greater thanthe height of the barrier are injected into the storage node, where they are read as changes incurrent flowing through the transistor.
Short-wave pass filter
When the lower gate is set to its threshold voltage of –3.5 V, the injection of one electron into the

http://www.photonics.com/printerFriendly.aspx?contentID=88509&Publication=2

2007/08/07

Photonics.com Printer Friendly View

2/2 ページ

storage node is read as one decreasing step in current. Higher voltages create shorter energy
barriers and allow electrons with less energy — those excited by longer wavelengths — to passinto the storage node. This effectively allows the device to function as a short-wave pass filter
controlled by lower gate voltage.
The upper gate voltage, on the other hand, can control the sensitivity of the device. The uppergate serves as a source for the transistor and can control the number of detected electrons; ahigher voltage increases the electron density in the electron reservoir and, thus, the number of
excited electrons, regardless of the lower gate voltage.
Because a detected infrared signal can be stored and later read out nondestructively, theresearchers note the potential of the device in large-scale silicon integrations or as part of anarray. Adjusting the device to pick up desired wavelengths will prove useful in material analysis
and in remote and thermal sensing applications.
Applied Physics Letters, May 28, 2007, 223108.

from photonics.com - 8/1/2007

http://www.photonics.com/content/spectra/2007/August/nanophotonics/88509.aspx

Advertisement

http://www.photonics.com/printerFriendly.aspx?contentID=88509&Publication=22007/08/07