TABLE OF CONTENTS Piezoelectric materials are either dielectrics or semiconductors. Mechanical fields and mobile charges in piezoelectric semiconductors can interact, and this is called the acoustoelectric effect. An acoustic wave traveling in a piezoelectric semiconductor can be amplified by the application of a DC electric field. The acoustoelectric effect and the acoustoelectric amplification of acoustic waves have led to piezoelectric semiconductor devices. The basic behavior of piezoelectric semiconductors can be described by a simple extension of the theory of piezoelectricity [121], Structural theories for plates and shells were derived in [122 124]. More references can be found in a review article [125].
Consider a homogeneous, one-carrier piezoelectric semiconductor under a uniform DC electric field 
. The steady state current is 
, where q is the carrier charge which may be the electronic charge or its opposite, 
is the steady state carrier density which produces electrical neutrality, and ? ij is the carrier mobility. When an acoustic wave u( x, t) propagates through the material, perturbations of the electric field, the carrier density and the current are denoted by E j, n and J i. The linear theory for small signals consists of the equations of motion, Gauss s law, and conservation of charge [121]
The above equations are accompanied by the following linearized constitutive relations:
where d ij are the carrier diffusion constants. Equations (14.1.1) can be written as five equations for u, 
and n
On the boundary of...
