ELECTRIC-FIELD-INDEPENDENT BAND-GAP SUPERPOSITIONING AT 1.3-MU-M IN AN INGAAS-INALAS STRAINED-LAYER SUPERLATTICE

We report on the electric-field dependent band-gap energy and near-gap absorption coefficient of a specially designed strained-layer superla ttice (SLS) employing tensile strained quantum wells and having a band -gap wavelength near 1.3 mu m. The SLS was grown by molecular-beam epi taxy on an InP substrate and consists of In0.43Ga0.57As wells (4.5-nm- thick) and In0.6Al0.4As barriers (6.75-nm-thick). For applied fields f rom zero up to at least 2.5 X 10(5) V/cm the band-edge absorption exhi bits a single peak, which we attribute to a field-independent superpos itioning of the heavy-and light-hole ground states, This result agrees with tunneling resonance calculations, which predict these hole state s to have the same zero-field energy and to undergo nearly identical S tark shifts. Absorption-coefficient changes of up to 10(4) cm(-1) were readily achieved with applied biases under 15 V, suggesting potential applications to optical modulator devices. (C) 1997 American Institut e of Physics.