Enhanced response over wavelength range of 7-12 µm for quantum wells in asymmetric micro-pillars.

Efficient coupling in broad wavelength range is desirable for wide-spectrum infrared light detection, yet this is a challenge for intersubband transition in semiconductor quantum wells (QWs). High-Q cavities mostly intensify the absorption at peak wavelengths but with shrinking bandwidth. Here, we propose a novel approach to expand the operating spectral range of the Quantum Well Infrared Photodetectors (QWIPs). By processing the QWs into asymmetric micro-pillar array structure, the device demonstrates a substantial enhancement in spectral response across the wavelength from 7.1 µm to 12.3 µm with guided mode resonance (GMR) effects. The blackbody responsivity is then increased by 3 times compared to that of the 45° polished edge-coupled counterpart. Meanwhile, the dark current density remains unchanged after the deep etching process, which will benefit the electrical performance of the detector with reduced volume duty ratio. In contrast to the symmetric micro-pillar array that contains simple resonance mode, the detectivity of QWIP in asymmetric pillar structure is found to be improved by 2-4 times within the range of 9.5 µm to 15 µm.

Enhanced absorption of infrared light for quantum wells in coupled pillar-cavity arrays.

Periodic pillars of semiconductor in sub-wavelength size can serve multiple roles as diffracting, trapping and absorbing light for effective photoelectric conversion which has been intensively studied in the visible range. Here, we design and fabricate the micro-pillar arrays of AlGaAs/GaAs multi quantum wells(QWs) for high performance detection of long wavelength infrared light. Compared to its planar counterpart, the array offers 5.1 times intensified absorption at peak wavelength of 8.7 µm with 4 times shrinked electrical area. It's illustrated by simulation that the normal incident light is guided in the pillars by HE11 resonant cavity mode to form strengthened Ez electrical field, which enables the inter-subband transition of n-type QWs. Moreover, the thick active region of dielectric cavity that contains 50 periods of QWs with fairly low doping concentration will be beneficial to the optical and electrical merits of the detectors. This study demonstrates an inclusive scheme to substantially raise the signal to ratio of infrared detection with all-semiconductor photonic structures.