Development of 13-μm cutoff HgCdTe detector arrays for astronomy

Abstract

Building on the successful development of the 10 µm HgCdTe detector arrays for the proposed NEOCam mission, the University of Rochester Infrared Detector team and Teledyne Imaging Systems are working together to extend the cutoff wavelength of HgCdTe detector arrays initially to 13 µm, with the ultimate goal of developing 15 µm HgCdTe detector arrays for space and ground-based astronomy. The advantage of HgCdTe detector arrays is that they can operate at higher temperatures than the currently used arsenic doped silicon detector arrays at the longer wavelengths. Our infrared detector team at the University of Rochester has received and tested four 13 µm detector arrays from Teledyne Imaging Systems with three different pixel designs, two of which are meant to reduce quantum tunneling dark current. The pixel design of one of these arrays has mitigated the effects of quantum tunneling dark currents for which we have been able to achieve, at a temperature of 28 K and applied bias of 350 mV, a well depth of at least 75 ke − for 90% of the pixels with a median dark current of 1.8 e − /sec. These arrays have demonstrated encouraging results as we move forward to extending the cutoff wavelength to 15 µm.

Mid-infrared detector development for the Origins Space Telescope

“…For the past three years, UR has been extending this technology to longer wavelength cutoffs. The results for 13-μm cutoff wavelength detector arrays were very promising with dark currents, well depths, and operabilities [23][24][25] similar to those of the earlier 10-μm cutoff wavelength detector array produced for NEOSM. For the 15-to 16-μm cutoff wavelength detector arrays produced in the second half of the UR development program, 26 the dark currents were higher and the well depths were lower than Origins requirements.…”

Characterization of a 15-μm cutoff HgCdTe detector array for astronomy

“…Even with this apparent increase in trap-to-band tunneling, the results obtained for this array are very encouraging as it shows an improvement in the array design by TIS in increasing the β parameter (see Cabrera et al (2019) 19 ), therefore reducing tunneling currents. The extrapolated band-to-band tunneling current fitted to H1RG-18509 (LW13 array designed to reduce tunneling currents) to a device with the same cutoff wavelength as H1RG-20303 would be ∼ 5 × 10 5 e − /sec with an actual reverse bias of 350 mV at a temperature of 23 K, about two orders of magnitude larger than what was measured for the pixel in Fig.…”

“…Following the reset of the array, a redistribution of charge due to the capacitive coupling to the reset FET can add 0-75 mV to the applied reverse bias. 5,19,24 The initial dark current can change considerably with respect to the detector bias on each individual pixel at the beginning of the integration ramp: we therefore measure the zero bias saturation level on the same ramp used to measure the dark current without resetting the array between measurements, allowing us to obtain the actual detector bias. The well depth is given by the detector bias for the first sample.…”

“…The other three LW13 arrays H1RG-18367, 18369, and 18508 had median dark currents of about 379, 730, and 780 e − /s at 28 K and applied bias of 350 mV, where the dark current at this bias is dominated by band-to-band or trap-to-band (defect assisted) tunneling. 19 An increase in band-to-band and defect assisted tunneling current was expected array-wide as the cutoff wavelength is increased to a target of 15 µm due to the smaller band-gap. The effect of trap-to-band is less predictable than band-to-band tunneling since it is dependent on the defect/dislocation density of individual pixels (see section 3).…”

“…Data from the LW10 2, 5, 6 and the LW13 19 devices have shown that a single trap density is not sufficient to model trap-to-band tunneling. Pixels that exhibit trap-to-band tunneling in those devices may show a soft breakdown in the I-V curves, followed by the onset of trap-to-band tunneling.…”