Quantum-cascade-laser structures as photodetectors

We evaluated two different quantum-cascade-laser structures as photodetectors. The first device was a 5.3 <i>µ</i>m two-phonon-resonance structure, and the second one a 9.3 <i>µ</i>m bound-to-continuum transition laser. The 5.3 <i>µ</i>m structure had a peak responsivity of 120 <i>µ</i>A/W at 2200 cm^–1 and functioned up to 325 K. On the other hand, the 9.3 <i>µ</i>m device also worked up to 297 K but had a lower responsivity of 50 <i>µ</i>A/W at 1330 cm^–1. Since the absorption peak of these devices can be shifted by applying an external bias, we envision interesting applications in free-space optical telecommunications.