THz absorbing AlGaN/GaN multi-quantum-wells: Demonstration of a robust 4-layer design

We report on AlGaN/GaN multi-quantum-well structures displaying intersubband absorption in the THz spectral range. Firstly, we theoretically analyze the weaknesses of the state-of-the-art GaN-based step-quantum-well architecture from an optoelectronic standpoint. We then propose a modified geometry with improved structural robustness considering the uncertainties associated to the growth. This later structure, consisting of 4layer quantum wells, has been grown by plasma-assisted molecular-beam epitaxy, and characterized structurally and optically. Low temperature absorption of samples with different Si doping levels confirms intersubband transitions in the far-infrared, centred at 28 μm.