Modulation of internal piezoelectric fields in strained-layer superlattices grown along the [111] orientation

Abstract

Large internal piezoelectric fields are generated when strained-layer superlattices are grown from III–V zinc-blende-structure compound semiconductors. The orientation of these internal fields depends on the components of the strain tensor and, consequently, on the growth orientation of the superlattice. In the usual case of strained-layer superlattices grown along the [001] axis, the piezoelectric fields vanish. However, the case of strained-layer superlattices grown along the [111] axis is particularly interesting because the internal piezoelectric fields are parallel to the growth axis and their magnitude typically exceeds 100 kV/cm for lattice mismatches as small as 1%. Therefore, [111]-oriented strained-layer superlattices exhibit novel physical properties and present technological opportunities not afforded by commonly grown [001]-oriented strained-layer superlattices. The internal strain-induced fields substantially modify the electronic structure and optical properties of [111]-oriented strained-layer superlattices. The presence of such large strain-induced polarization fields in [111]-oriented strained-layer superlattices is a physically interesting and technologically significant feature because of the possibility of modulating these internal fields by the application of an external field. Examples of modulating fields include (i) screening by photogenerated free carriers, (ii) external electric bias, or (iii) applied uniaxial stress. As a consequence of these modulations, large nonlinear optic, electro-optic and piezo-optic effects result. These effects are illustrated by calculations performed for Ga1−xInxAs–Al1−yIny As strained-layer superlattices grown along the [111] axis.