Reduction of noise in very long wave infrared quantum cascade detectors

Noise in quantum cascade detectors is studied experimentally and theoretically. Measurements were performed in dark conditions on a quantum cascade detector operating at 14.5 μm, in the very long wave infrared range. To investigate the signal-to-noise contributions of each intersubband transition involved in the transport, a model of noise has been developed. It is based on a noise equivalent electrical circuit of the quantum cascade detector. Non-radiative diagonal transitions (fundamental state to levels of the cascade structure) are identified as dominant contributions to the dark current and noise in the measured device. Based on these theoretical considerations, new optimized structures for the very long wave-infrared range are designed and exhibit a noise reduction down to a factor three at optimum responsivity.