Very large Stark shift in three-coupled-quantum wells and their application to tunable far-infrared photodetectors

Abstract

The quantum-confined Stark effect in the three-coupled-quantum-well (TCQW) structure is studied theoretically in this paper. The basic TCQW structures are composed of three quantum wells separated by two thin barriers. Coupled one-dimensional Schrödinger and Poisson equations are solved self-consistently to find the sub-band eigenenergies and the envelope wave functions for the TCQW structures. Results indicate that the GaInAs/AlGaAs/GaAs two-depth TCQW structure exhibits both a very large Stark shift and a high absorption coefficient for the 1→3 intersub-band transition. By using a 1→3 intersub-band Stark shift in the two-depth TCQW structure, a highly sensitive tunable far-infrared photodetector is proposed. This photodetector is ideal for device applications in the 8–14 μm atmospheric window region. The operation of this device is based on the infrared absorption by electrons in the ground state transited from the ground-state sub-band E1 of the TCQW to the second-excited-state sub-band E3. A very large variation of eigenenergy spacing ΔE31 between E3 and E1 under an applied electric field can be achieved. Since the infrared radiation is absorbed via the intersub-band resonance absorption (ℏω=E3−E1), the detected infrared wavelength can be tuned by the ΔE31 which can be adjusted by an applied electric field. Based on the theoretical calculations, a tuning range from 7.4 to 14 μm is predicted for the two-depth TCQW structure. This tuning capability is achieved by varying the applied electric field in the 60 to −60 kV/cm range.