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I want to learn differences between Infrared sensor fabrication and standard CMOS IC fabrication. If I am not wrong, in standard CMOS fabrication Silicon is mostly used. But for infrared spectrum such materials (HgCdTe, InSb and InGaAs ) are preferred.

Thank you,

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2 Answers 2

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Standard CMOS ICs are always based on Silicon. Always. No exceptions. So not "mostly" but always.

Fabrication of an IR sensor is something completely different.

OK, they might uses similar fabrication steps but that will be it. The materials used will be different.

It is also possible to create an IR sensor in CMOS technology. It will have different characteristics than HgCdTe, InSb and InGaAs based sensors though.

But I have yet to see a CMOS IC manufacturing process where HgCdTe, InSb or InGaAs is used. In CMOS fabrication they want to limit the usage of other materials than Silicon as this might cause leaking PN junctions resulting in non-working circuits.

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  • \$\begingroup\$ Hello @Bimpelrekkie, Thank you for reply. I need to learn advantages of InGaAs material over HgCdTe ( and also Si) in the infrared detector fabrication. What is not the enough thing in the HgCdTe ( or Si) that causes the InGaAs material have began to use in infared detector fabrication. \$\endgroup\$
    – doner_t
    Dec 18, 2017 at 21:41
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CMOS camera array detectors are bolometers = rely on creating small pixels which absorb IR light and heat up. This change in temperature are detected.

CMOS cameras are slow, milisecond range. Photon detectors below are fast, microsecond-nanosecond range.

InGaAs, InSb, HgCdTe are compound semiconductor (direct = large absorption) used to make photon detectors - the IR light on detector is absorbed = exchanged from photons to electrons, to create current/voltage change usually in specially designed layers stacks of semiconductor material forming PIN detector.

Detectors and arrays from compound semiconductors, are not broad spectrum (absorb light only in certain wavelength range - just like we do see only in visible range).

InSb = 1-5µm range, HgCdTe as ternary could span from 1µm (CdTe) till ~20µm (in principle around 0.1 cadmium molar fraction there is 0 bandgap, and HgTe is semi-metal).

Silicon fabs do not process III-V/II-VI semiconductors, because they could "contaminate" process equipment.

III-V/II-VI fabs use different chemistry for etching than Si.

InGaAs is used for NIR 1-2.6µm range, whereas HgCdTe (II-VI) IR detectors start from 2.6-17µm eSWIR-MWIR-LWIR-VLWIR (300K).

InGaAs is harder, more durable material and as III-V could withstand higher operating temperatures eg. 120-130C is still OK, whereas HgCdTe degrade (diffusion) from 120C.

Recently HgCdTe is being replaced due to ROHS by so called T2SL (Type 2 superlattices), which are combination of InAsSb-InAs, InAs-GaSb which could operate till ~10µm.

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