Search

One of the key features of quantum well infrared photodetectors is the narrow absorption band. However, some applications, as the infrared spectroscopy, require broadband detection. Several approaches have been used to get a broadband response with QWIPs (superlattices, digital graded barriers, stacks, etc.). In this paper, we focus on the interlaced configuration and on the coupled wells structure. Both designs exhibit broadband response covering the [11-15 m] spectral range. The experimental dependencies of the spectral shape versus the temperature and bias voltage are discussed. Based on numerical model, we propose a specific design strategy which leads to a spectral shape quasiindependent on the operating conditions.

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 m, 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.