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