Bandgap-Engineering of HgCdTe for Two-Color Ir Detector Arrays BY Movpe
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Mat. Res. Soc. Symp. Proc. Vol. 484 0 1998 Materials Research Society
QE in the range of 70-75%. In addition, independently accessed, p-n-N-P two-color HgCdTe detectors' and 64x64 focal plane arrays 3 (FPA) were demonstrated, that operate simultaneously in the MW and LW spectral bands. The QE and detectivities of these detectors approach those achieved in state-of-the-art single band detectors in the respective spectral bands. In this paper new results are reported for MOVPE growth of stacked two-color IR detectors in the double-heterojunction p-n-N-P configuration that operate simultaneously in the3 MW (3-5 jim) and LW (8-12 jim) spectral bands. As compared to our previous demonstration of two-color detectors, a barrier layer between the MW and LW absorber layers has been introduced to minimize spectral cross-talk between the two detectors. Repeatability results based on SIMS analysis are reported for a series of thirteen films grown under nominally identical conditions. X-ray double crystal rocking curve (DCRC) mapping data, and dislocations in the two-color detector films evaluated by etch pit density (EPD) depth profiles through the film thickness, are presented. THE p-n-N-P TWO-COLOR DETECTOR Lockheed Martin's independently accessed, backside illuminated, simultaneous, p-n-N-P two-color HgCdTe detector is based upon an LW p-on-n heterojunction on top of an N-on-P MW heterojunction grown in situ on nominally lattice-matched CdZnTe. We have shown 3 that this device architecture allows the fabrication of FPAs with high QE and detectivities at 78 K. The spectral response data showed well behaved sharp profiles corresponding to the compositions of the absorber layers. The LW --+ MW spectral crosstalk was measured to be at 0.4% but a more significant MW -* LW spectral crosstalk was observed. The latter was attributed to spillover of photocarriers from the MW absorber layer to the LW junction. To eliminate the residual MW -LW crosstalk a small composition barrier has been added at the MW/LW absorber layer interface. A cross-section of the double-heterojunction p-n-N-P two-color IR detector design with the barrier layer and its energy band profile is shown in Figure 1. Two indium bump interconnects in each detector provide independent electrical access to the LW and MW photodiodes and allow the respective photocurrents to be separated. The wide gap SW p-type layer serves as the common contact. Lw ap-avper p
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Figure 1. Cross section and energy band profile for the simultaneous p-n-N-P two-color HgCdTe detector with a composition barrier. 234
MOVPE GROWTH AND CHACTERIZATION MOVPE growth of the multilayer HgCdTe films was carried out by the interdiffused multilayer process (IMP) which involves the growth of alternating thin layers of HgTe and CdTe that are subsequently allowed to interdiffuse at the growt
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