Broadband Photocurrent Enhancement in Longwave Infrared Quantum Dot Photodetectors by Sub-Wavelength Surface Gratings

Broadband photocurrent enhancement covering the wavelength range from 4 m to 11 m is observed. A 4.6 times (4.6x) photocurrent enhancement is obtained at the photodetection wavelength of 8.7 m. By comparing the simulated diffraction efficiency with the photocurrent enhancement spectrum, we attribute the enhancement to the 1st-order diffraction of the normal infrared (IR) incidence radiation. The photodetectivity (D*) enhancement at different biases is also measured and analyzed.