Refractive index of high-carrier-doped InGaAs/AlAsSb coupled double quantum wells

The carrier density dependence of the refractive index of Si-doped InGaAs/AlAsSb coupled double quantum wells (CDQWs) was studied. The refractive index of the CDQWs changed due to two effects that arose from: (1) a change in the optical absorption and (2) the carrier plasma effect. The refractive index changes due to these two effects were separately evaluated by experimental methods and found to agree well with reference values obtained by a prism coupling technique. By considering the carrier density dependence of the refractive index of the CDQWs and the fundamental requirements for practical devices, we found that the carrier density of the CDQWs should be low with sufficient optical absorption strength due to intersubband transitions