Coupling efficiency of infrared radiation to electron intersubband transition in quantum well infrared photodetector by a two-dimensional (2D) grooved grating is examined. A resonant enhancement of the coupling efficiency at a certain optimal groove depth is predicted and confirmed experimentally. It is argued that a detector with a properly designed ordered cross grating performs better than a detector with optimized 2D random grating. In a detector with ordered grating a quantum efficiency of 75% is obtained with a doping level of only 3.5×1017cm−3 in each quantum well and dark current density of 0.34 mA/cm2 at 78 K.

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