Second-order optical nonlinearities in materials are of paramount importance for optical wavelength conversion techniques, which are the basis of new high-resolution spectroscopic tools. Semiconductor technology now makes it possible to design and fabricate artificially asymmetric quantum structures in which optical nonlinearities can be calculated and optimized from first principles. Extremely large second-order susceptibilities can be obtained in these asymmetric quantum wells. Moreover, properties such as double resonance enhancement or electric field control will open the way to new devices, such as fully solid-state optical parametric oscillators.
We present the results of a new model for the simulation of quantum well infrared photodetectors (QWIPs) both in dark conditions and under illumination. This model takes into account the elementary mechanisms involved in the detection process (injection at the contacts, balance between capture and emission in each well) in a self-consistent way. The main feature emerging from the model is the redistribution of the electric field along the structure in order to maintain current conservation. The calculated dark current, electrical noise, responsivity, and detectivity of different QWIP structures are compared with experimental measurements and the agreement is found to be fairly good. This model may be considered as a step toward more powerful simulation tools for QWIPs.
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