ELECTROOPTIC EFFECTS OF PIEZOELECTRICALLY STRAINED ALGAAS/GAAS(111) QUANTUM-WELLS

The electrooptic effects, electroabsorption and the electric field induced change in birefringence (electrobirefringence), have been measured in 100 angstrom (111) and (100) GaAs/AlGaAs quantum wells. It is determined that electrobirefringence at lambda = 1.06-mu-m is 43% larger in (111) quantum wells than in (100) oriented wells. The primary cause of this increased electrobirefringence of (111) oriented wells is the anisotropy of the effective mass of the heavy holes. The increased effective mass of the heavy hole in the (111) direction causes a larger quantum confined Stark effect, which causes larger electrobirefringence. A mass anisotropy for light holes is also observed. A second effect, the converse piezo-electric effect (electric field induced strain), exists in the (111) wells, and is an additional contribution to the difference between the electrooptic effects of the two orientations. The electric field dependent strain of the (111) wells shifts the exciton absorption features, as does the quantum confined Stark effect. Unlike the quantum confined Stark effect, however, the electrooptic effects induced by the converse piezo-electric effect should be dependent on the sign of the electric field. This dependence of the electrooptic behavior on the sign of the electric field has been observed in (111) quantum wells.