Sias Ibc Detectors

The most difficult requirement for the MIRI detectors is high Quantum Efficiency (QE) over the full spectral range and low dark currents. The relative response per photon as a function of wavelength is shown in Fig. 1 for three Si:As IBC detector material types.

0 K MIRI Assy 7581011.1 Wafer 9601/A05 9/22/2004

& Assy 7581009.1 Wafer 9581/A05; Diodes D28 at -1.0 V Bias

0 K MIRI Assy 7581011.1 Wafer 9601/A05 9/22/2004

& Assy 7581009.1 Wafer 9581/A05; Diodes D28 at -1.0 V Bias

-9601 @ - 1.0 volt -hanger queen @-1.0 volt 9581 @ -1.0 volt_

-9601 @ - 1.0 volt -hanger queen @-1.0 volt 9581 @ -1.0 volt_

Wavelength (^m)

Figure 1. Relative spectral response measurements for three Si:As IBC detector materials: MIRI baseline (top curve), MIRI contingency (middle curve), and material similar to that used on Spitzer/IRAC (bottom curve). The MIRI material has higher response in the 5 to 10 ^m spectral region than Spitzer/IRAC.

All these materials have nearly 100% internal QE at ~15 ^m; thus these relative response curves are nearly the same as responsive QE (gain=1) if the detector has perfect Anti-Reflection (AR) coating. The material used as the baseline for MIRI exhibits the highest response. The middle curve is a material with a thinner detecting layer, processed as a "contingency" in case

0.01

20.0

25.0

30.0

the more difficult-to-produce baseline wafer failed to yield. The bottom response curve is a material similar to that flown on Spitzer/IRAC. Notice that response of the MIRI baseline material is approximately 60% higher than the Spitzer material at 5 ^m. Since bare silicon reflects approximately 30% of the incident light, AR coatings have been developed for MIRI to reduce reflection losses. One coating has a minimum reflectance at 6 ^m and the second has its minimum at 16 ^m. Low dark current has also been achieved with MIR detectors, but due to the difficulty in measuring such low currents, the measurements must be made at the SCA level. The results are described in Section 4.

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