Stark Shifts In Mid-Infrared Type Ii Quantum Well Transitions

We have studied electric field induced (Stark) shifts in mid-infrared (IR) transitions that occur in type II AlSb/InAs/GaSb quantum wells. Because of the spatial separation of the electron and hole wave functions in the type II system, the potential drop between the layers dominates the shift in the real-space-indirect transition energies when an external electric field is applied. This can result in either a redshift or a blueshift, depending on the ordering of the quantum well layers within the intrinsic region of a p-i-n diode. The case in which a reverse bias on the diode yields a blueshift in the transition energy is of particular interest for IR electro-optic device applications. The modulator section of an integrated source/waveguide modulator would strongly absorb at zero bias and could be biased into transparency, and bistable optical switches could be made more efficient than with redshifting devices. We have used low temperature current-voltage, capacitance-voltage, and photocurrent measurements to characterize a type II quantum well structure that exhibits a blueshift in the lowest energy transitions that is roughly linear with applied bias and is comparable to the potential drop across the structure. (C) 2010 American Institute of Physics. [doi:10.1063/1.3383040]