Normal incidence infrared modulator using directndash;indirect transitions in GaSb quantum wells

摘要

We propose a novel normal incidence infrared modulator using the directndash;indirect transitions induced by an applied electric field in GaSb quantum wells (QWs). The device is based on the principles that the quantumhyphen;confined Stark shift is proportional to the effective mass, and that the interconduction subband absorption at normal incidence is forbidden in directhyphen;gap QWs but allowed in indirecthyphen;gap QWs. Since the effective mass of theLvalleys is larger than that of the Ggr; valley, the corresponding Stark shift is also larger. As a result, the ground state of a QW associated with the Ggr; point at zero voltage becomesLstate under bias (directndash;indirect transition). Consequently the device switches from being transparent to normal incidence light to strongly absorbing it. Based on our calculations for a GaSb/Ga0.5Al0.5Sb QW with a well width of 85 Aring;, changes in absorption coefficients up to 104cmminus;1in the modulation wavelength range of 14ndash;18 mgr;m could be achieved under an electric field in the range of 200 kV/cm. This is the most effective mechanism ever reported for normal incidence infrared modulators. thinsp;