Voltage-tunable two-colour quantum well infrared detector with Al-graded triangular confinement barriers

We report on a novel voltage-tunable stacked bound to quasi-continuum quantum well infrared detector designed to work in two of the atmospheric windows (3-5 and 8-12 µm). In order to improve the growth process by molecular beam epitaxy, the abrupt interfaces between different Al-content layers were eliminated. A different choice based on Al-graded triangular confinement barriers was used instead. This device can be voltage controlled due to the formation of field domains in the stacked structure when an external bias is applied. This results in a voltage drop across the detectors proportional to their series resistance. Besides, a significant photovoltaic response was achieved in the 3-5 µm region and attributed to an unintentional asymmetry in the potential profile for the detector operating in this range.