Nonlinear optical response of [111] growth axis strained-layer superlattices

Abstract

The presence of internal strains in [111] growth axis strained-layer III–V superlattices leads to the generation of large polarization fields (exceeding 100 kV/cm) because the constituent semiconductors are piezoelectric. These strain-induced polarization fields produce a substantial reduction of the superlattice band gap and cause a spatial separation of the electrons and holes in the confining layers in such a way as to screen the internal fields. When free carriers are present to screen the strain-induced piezoelectric fields, the electronic structure (energy band gap, in-plane effective masses) and the optical response (absorption edge, optical constants) of the strained-layer superlattice depend on the density of free carriers. In the case where the electrons and holes are photogenerated, the superlattice photoabsorption profile can be modified by variations of the intensity of the optical excitation. The nonlinear optical response of strained-layer superlattices owing to free-carrier screening of strain-generated internal fields is illustrated here for the case of Ga1–xInxAs–Al1–yInyAs strained-layer superlattices.