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Abstract

An integrable photodetector element of large dynamic range includes a silicon substrate which has a resistivity of between 1 and 100 ohm-cm. The substrate is of one conductivity type. In the substrate there is an electrically floating photosensitive diffusion region and a second diffusion region that is spaced apart from the electrically floating region by means of a channel in the substrate. The two diffusion regions are of the same conductivity type and of opposite conductivity type to that of the substrate. A metal-insulator-semiconductor gate spans the substrate between the regions and over the channel. The gate is electrically connected to the electrically floating region, and the second region is reverse biased with respect to the substrate. Except for the photosensitive diffusion region, the element is shielded against penetration by visible light. The length of the channel between the regions, the resistivity of the substrate, the magnitude of the reverse bias and the depth of the diffusion regions is selected so that the potential barrier between the electrically floating region and the channel is low enough that electrons which are photogenerated in response to visible light impinging on the electrically floating region can be injected therefrom into the channel to be collected by the second diffusion region. As a result of this the voltage of the electrically floating region varies logarithmically with changes in visible light incident thereon.

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