Voltage-tunable far-infrared photodetector with a very large tuning range

A highly sensitive tunable far-infrared photodetector using the 1 → 2 intersubband Stark shift in compositionally asymmetric coupled quantum cells (CACQWs) is proposed here. The operation of this device is based on the infrared absorption by electrons in the ground state transited from the ground-state subband E1 of the CACQW to the first-excited-state subband E2. A very large variation of eigenenergy spacing ΔE21 (E2 − E1) under an applied electric field can be achieved. Since the infrared radiation is absorbed via the intersubband resonance absorption ([hstrok]ω = E2 − E1), the detected infrared wavelength can be tuned by the ΔE21 which can be adjusted by the applied electric field. Based on theoretical calculations, a tuning range from 8 to 16 μm is predicted. This tuning capability is achieved by varying the applied electric field in the 90 to −60 kV/cm range. The absorption coefficient is evaluated by the density-of-state formalism and a very large absorption coefficient is obtained for the proposed CACQW structure.