The 1/f noise in photovoltaic (PV) molecular-beam epitaxy (MBE)-grown Hg
1−xCd
xTe double-layer planar heterostructure (DLPH) large-area detectors is a critical noise component with the potential to limit
sensitivity of the cross-track infrared sounder (CrIS) instrument. Therefore, an understanding of the origins and mechanisms
of noise currents in these PV detectors is of great importance. Excess low-frequency noise has been measured on a number of
1000-μm-diameter active-area detectors of varying “quality” (i.e., having a wide range of I-V characteristics at 78 K). The
1/f noise was measured as a function of cut-off wavelength under illuminated conditions. For short-wave infrared (SWIR) detectors
at 98 K, minimal 1/f noise was measured when the total current was dominated by diffusion with white noise spectral density
in the mid-10
−15A/Hz
1/2 range. For SWIR detectors dominated by other than diffusion current, the ratio, α, of the noise current in unit bandwidth
i
n(f = 1 Hz, V
d = −60 mV, and Δf = 1 Hz) to dark current I
d(V
d = −60 mV) was α
SW-d = i
n/I
d ∼ 1 × 10
−3. The SWIR detectors measured at 0 mV under illuminated conditions had median α
SW-P = i
n/I
ph ∼ 7 × 10
−6. For mid-wave infrared (MWIR) detectors, α
MW-d = i
n/I
d ∼ 2 × 10
−4, due to tunneling current contributions to the 1/f noise. Measurements on forty-nine 1000-μm-diameter MWIR detectors under
illuminated conditions at 98 K and −60 mV bias resulted in α
MW-P = i
n/I
ph = 4.16 ± 1.69 × 10
−6. A significant point to note is that the photo-induced noise spectra are nearly identical at 0 mV and 100 mV reverse bias,
with a noise-current-to-photocurrent ratio, α
MW-P, in the mid 10
−6 range. For long-wave infrared (LWIR) detectors measured at 78 K, the ratio, α
LW-d = i
n/I
d ∼ 6 × 10
−6, for the best performers. The majority of the LWIR detectors exhibited α
LW-d on the order of 2 × 10
−5. The photo-induced 1/f noise had α
LW-P = i
n/I
ph ∼ 5 × 10
−6. The value of the noise-current-to-dark-current ratio, α appears to increase with increasing bandgap. It is not clear if
this is due to different current mechanisms impacting 1/f noise performance. Measurements on detectors of different bandgaps
are needed at temperatures where diffusion current is the dominant current. Excess low-frequency noise measurements made as
a function of detector reverse bias indicate 1/f noise may result primarily from the dominant current mechanism at each particular
bias. The 1/f noise was not a direct function of the applied bias.
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