FEMTOSECOND SATURABLE ABSORPTION RECOVERY IN A TYPE-II TUNNELING BI-QUANTUM WELL FOR LONG-WAVELENGTH OPERATION

We demonstrate femtosecond bleached absorption recovery using a type-I l tunneling biquantum well (TBQ) structure tailored for long-wavelengt h operation. The type-IT TBQ structure consisted of strained-layer InG aAlAs narrow wells and InGaAsP wide wells with staggered band lineup, separated by thin InAlAs barriers. In the structures, the photocreated electrons in InGaAlAs layers energetically relax to InGaAsP layers vi a LO-phonon assisted tunneling through InAlAs barrier! resulting in th e bleaching recovery due to the ultrafast spatial separation of electr ons and holes. The bleached absorption recovery time was as fast as 35 0 fs in the excitation wavelength range of 50 nm near the InGaAlAs ban dgap.