Flexible photodiode process delivers high efficiency

21st October 2014

Mick Elliott

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PREMA Semiconductor develops silicon photodiodes with adapted spectral sensitivities. While light with short wavelengths is absorbed by the initial microns, the penetration depth for light with longer wavelengths varies a lot. Therefore, the spectral sensitivity of photodiodes can individually be adapted by the position of the pn‑junction.

Several photodiodes with selective sensitivities in the visible or the infrared range are already offered by PREMA.

The ModuS U6 process from PREMA Semiconductor utilised for production affords a flexible fabrication of ICs with photodiodes having several sizes or being arranged in arrays. Besides spectral sensitivity, a spacial resolution becomes feasible. Circuits for analysis as low-pass filters, amplifiers or position detection can be also integrated. A low density of defects results in an extraordinary performance with small dark currents and high efficiency.

Using photodiodes for detecting an integral light spectrum, types with common transparent protective coatings can be offered at convenient prices. For monochromatic measurements with high-precision an anti-reflective coating has to be applied. Thus, the entire light spectrum is coupled into the silicon by using a layer with appropriate index of reflexion and thickness.

Having a special geometry, a photodiode with short response times has been developed for applications such as optical encoders or IR receivers. Their capacity is reduced to a minimum of < 20 pFmm^-2 even without any applied reverse voltage.