Intersubband transitions in InGaAs/AlAsSb coupled double quantum wells with InAlAs coupling barriers

We have fabricated a novel InGaAs/AlAsSb coupled double quantum well (C-DQW) with InAlAs coupling barrier for use in all-optical switches based on intersubband transitions (ISBTs). Strong well -well coupling produced by the low potential of the InAlAs coupling barrier shortens the ISB-T wavelength. The FTIR measurements show that the wavelength of ISB absorption decreases to 1.53 mum when the InGaAs wells and InAlAs coupling barrier in the C-DQW consist of 9 and 4 monolayers (MLs), respectively. Moreover, the absorption coefficients at 1.55 mum increase significantly above 500 cm-1 and are therefore equivalent to those of the conventional C-DQW that consists of AlAsSb and AlAs coupling barriers. It is confirmed that the ISB-T wavelength can be reduced effectively by reducing the potential height of the coupling barriers as well as the thicknesses of the wells and coupling barriers.