Silicon is generally, without modification in the chip such as deep trench isolation, not that sensitive to NIR. This means that in some cases alternative materials such as InGaAs or Ge are deployed. Organic semiconductors have now shown excellent results with 65% EQE at NIR. Silicon- even with modification- struggles to reach this level of performance.
Silicon is generally not very sensitive to NIR. As such many approaches are being developed to make it sensitive to NIR.
One such approach is to develop hybrid sensors consisting of organic or quantum dots atop a specially designed Si CMOS ROIC (read-out-circuit).
In such approaches the EQE is generally not high- it hovers around the 20% mark. In the case of this development, demonstrated by Raynergy Tek, an advanced materials firm in Taiwan focusing mainly on organic photodetectors and organic photovoltaics, the EQE has reached 65% at 940nm.
The device structure is shown below. Of course, to the best my knowledge, these appear to be hero cells made on a glass substrate.
They are still a far cry from a true solution processed organic on CMOS hybrid imager with a resolution of VGA and above.
To get there, many developments will still be needed including the development of a special ROIC, the development of a process to cast (or otherwise deposit) the entire OPD stack onto of the CMOS ROIC, patternig it without loss of EQE, ensuring stability, etc
Nonetheless, this is a fantastic demonstrator, showing the potential.
In subsequent posts I will discuss other approaches towards NIR and even SWIR sensing, starting with full silicon approaches then going towards hybrid QD- or Organic-CMOS approaches. If we get the chance, we will also highlight some innovations in InGaAs-on-Silicon technology which is overcoming the traditional limitaitons of this approach, e.g., large pixel size above 10um.
Of course, we should emphasis here that these organic NIR OPDs need not be neccessarily used in a hybrid CMOS structure. They could be standlone NIR sensors or even large area ones. However, results on flexible substrate or in large-area sensor formats, including active matrix ones, are yet to be annonuced.
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