Piezoelectric effects in strained-layer superlattices

Abstract

Because zinc-blende structure semiconductors are piezoelectric, polarization fields can be generated in the constituent materials of strained-layer superlattices by lattice-mismatch-induced strain. The orientation of the polarization fields depends on the superlattice growth axis. Because one of the constituent layers of the superlattice is in biaxial tension and the other is in biaxial compression, the sign of the polarization field is opposite in the two constituent layers making up the superlattice period. Thus, sheets of divergence of polarization occur at the interface for a longitudinal induced polarization and sheets of curl of polarization occur at the interface for a transverse induced polarization. For a [111] growth axis, the induced polarization is purely longitudinal; for a [110] growth axis, the induced polarization is purely transverse. For a general growth axis the induced polarization has both longitudinal and transverse components. The sheets of divergence of polarization generate internal electric fields and the sheets of curl of polarization generate internal electric displacement fields. The internal electric fields are always purely longitudinal and the internal electric displacement fields are always purely transverse. The magnitude of these fields can be very large.