Extended InGaAs Image Sensors Questions & Answers

Why are there more extended InGaAs image sensors in the market now?

Due to fabrication challenges in the past, previous InGaAs image sensors with extended spectral response—or extended InGaAs for short—had extremely high dark current and low signal-to-noise ratio because extended InGaAs requires a mismatched lattice of InGaAs and InP (Fig. 1), which lowers the quality of the film and increases the dark current. Also, the pixel pitch had size limitations and couldn’t be made smaller than a certain size. But due to improvements in the fabrication process and design capability, extended InGaAs image sensors now have lower dark current (Fig. 2) and smaller pixel pitch.

Figure 1. Lattice structure for standard InGaAs and extended InGaAs

Figure 2. Example of improved dark current for InGaAs image sensor with 2.6 µm cutoff wavelength

What are the pros and cons of extended InGaAs image sensors?

Thanks to improvements in the fabrication process, Hamamatsu now offers extended InGaAs image sensors with cutoff wavelengths ranging from 1.8 µm to 2.5 µm (Fig. 3). These extended InGaAs image sensors are alternatives to mercury cadmium telluride (HgCdTe or MCT) sensors, which have been often used to detect 1.7-2.5 µm wavelengths. Compared to HgCdTe, InGaAs is easier to handle because it is not as brittle as HgCdTe and doesn’t include any RoHS-restricted compounds such as mercury and cadmium. Also, extended InGaAs has better linearity and less cooling requirements. But the disadvantage of extended InGaAs sensors is that its bandwidth is not as broad as that of HgCdTe sensors.

Figure 3. Example spectral response ranges of extended InGaAs image sensors

Could I customize an InGaAs image sensor with multiple cutoff wavelengths?

Yes. Unlike silicon image sensors that could grow on CMOS, InGaAs image sensors are composed of an InGaAs photodiode array bonded or wired to a readout integrated circuit (ROIC). Therefore, Hamamatsu can combine multiple InGaAs photodiode arrays with different cutoff wavelengths on a single ROIC (Fig. 4). Please contact us to start a discussion about your customized image sensor.

Figure 4. Example of a customized InGaAs image sensor with multiple cutoff wavelengths on one ROIC

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Meet the engineer

Albert Tu is a Marketing Engineer working on NIR/SWIR applications. He’s been helping customers find the right solution for their technology, and he’s developing new business by exploring potential technologies. Albert’s experience in high-tech industry and startups allows him to identify the need first and to find the right solution to solve it. Recently, he enjoys cooking in his spare time and likes to try out new recipes.