Electric coupling properties of acoustic and electric surface waves

Abstract

A discussion is given of electric coupling across in interface between various kinds of surface waves on solids. This leads to a unified treatment of the propagation and coupling properties of such phenomena as electrostatic energy carrier waves on semiconductors. Rayleigh waves on piezoelectric media and Bleustein-Gulyaev waves. The influence of an electric drift field and of a transverse magnetic field is included and much attention is paid to amplification and related phenomena. The central quantity in the treatment is the effective dielectric constant ϵ eff with which a half-space of material can be characterized. Ingebrigssen's approximation of this quantity for the case of Rayleigh waves is analyzed and shown to be realistic in many interesting situations. New effects, derived in this paper are: 1) a tendency of Bleustein-Gulyaev waves to turn “leaky”. i.e., to radiate acoustic energy away from the interface when electrically coupled to a semiconducting adjacent medium which is subjected to an electric drift field and to a transverse magnetic field; 2) a tendency of acoustic surface waves to acquire low phase velocities if this magnetic field becomes large and has the proper direction; 3) an interdigital electrode structure on a non-plezoelectric semiconductor which is subjected to a d.c. electric drift field may exhibit a negative a.c. conductance. The relevance of ϵ eff for the electrical excitation of surface waves is also shown to be considerable and some difficulties associated with previous treatments of the excitation problem are discussed in terms of ϵ eff.