Mitsubishi Electric Corp developed what it claims is an infrared sensor having the world's highest sensitivity.

The sensor realizes a sensitivity that is more than 10 times higher than that of quantum-type infrared sensors, which had the highest sensitivity. This time, Mitsubishi Electric used graphene (carbon material) and utilized its high electron mobility.

Graphene channels controlled for detecting infrared light

The newly-developed sensor detects middle-infrared light. A device mounted with graphene is formed in the channel part of an FET (field effect transistor), and a light-amplifying part that produces electrons and positive holes at the time of receiving infrared light is placed under the graphene.

Moreover, a negative electric potential (back gate voltage) is applied to the light-amplifying part from the side opposite to the graphene. At this point, when the light-amplifying part receives infrared light, electrons generated by the back gate voltage gather on the graphene side in response. Those electrons are used to change the channel characteristics realized by the graphene.

Fig 1: Graphene is used to increase sensitivity to middle-infrared light. At a very low temperature of, for example, 80K (low thermal noise), the sensitivity can be increased by 100 times. In this image, InSB is used in the light-amplifying part, but it is possible to use other materials.

The current-voltage characteristics applied to both side of the graphene are changed by the electrons generated by infrared light. In the right graph of Fig 1, the "VDP" current increases due to electrons generated by infrared light. The current (⊿Iph) increases because of the high electron mobility of graphene and the steep angle of the graph, increasing sensitivity. When an index of sensitivity was measured, it turned out that sensitivity had increased by 1,000%.

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