Bulk grown wafers had been used for fabricating photoconductive (PC) HgCdTe detectors for several decades until recent years. As bulk wafers are getting gradually depleted over years, epitaxial grown HgCdTe wafers are becoming the only choices available. This paper reports the very long wavelength Infrared (VLWIR) PC HgCdTe detector development (cutoff wavelength ~ 17μm at LN2) at Teledyne, leveraging the state-of-the-art molecular beam epitaxy (MBE) material technology on CdZnTe substrates. These MBE wafers provide much larger wafer sizes, better uniformity, and in general better detector performance than conventional bulk wafers. Detailed detector performance comparison was performed between MBE and bulk wafers on detectivity (D*), responsivity, spectral response, etc. for 1mm and 0.25mm discrete detectors. The VLWIR MBE PC HgCdTe detectors are now in volume production at Teledyne.
This paper presents performance of very long wavelength infrared HgCdTe detectors operating at 60K for space surveillance and earth observation applications. Fabricated detector arrays were hybridized to Teledyne’s GeoSnap- 18 1024 x 512 read-out integrated circuit of 18-micron x 18-micron pixel format. This is a capacitive transimpedance amplifier pixel design with high linearity. Detector focal plane arrays are made of Teledyne’s high quality molecular beam epitaxy grown HgCdTe infrared detector materials with detector cut-offs near 13.5 microns at 60K. Key detector performance parameters of high operability with low dark currents, high quantum efficiency was demonstrated. One of the FPA was baked at 70oC under vacuum environment for 42 days; pre- and post-bake performance was compared. Dark current operability increased from 94% to 97% for pixels having dark currents ≤ 1.08E9 e-/s/pxl and noise operability also increased from 91% to 94% for pixels having total dark noise ≤ 815 e-/pxl. Obtained minimum dark current is on the order of 3E7 e-/s/pxl, which is a factor of four lower than the RULE07 for 13.24 microns cut off at 60K.
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