Internal waves of free charge carriers in semiconductors

We show that internal waves that are similar to internal gravity waves in the ocean can propagate in semiconductors with a gradient of free charge carrier concentration. Unlike internal gravity waves in the ocean, which are observed at infrasonic frequencies, the waves under consideration are excited in the microwave range, which opens up interesting possibilities for creating new types of electron devices. In the nonlinear rigime such waves assume the form of solitons described by the KdV equation.