AMPLIFICATION OF MAGNETOSTATIC SURFACE WAVES BY INTERACTION WITH DRIFTING CHARGE CARRIERS IN CROSSED ELECTRIC AND MAGNETIC FIELDS

The dispersion relation for propagation of electromagnetic waves along the interface between a low-loss ferrite and a high-mobility, current-carrying semiconductor film has been determined. The waves described by this relation resemble magnetostatic surface waves, except that they grow rather than decay provided that the direct current flowing through the semiconductor film exceeds a certain threshold value. The gain induced by the presence of the semiconductor film is negative at very small wavenumbers, becomes positive as the phase velocity of the guided waves becomes smaller than the drift velocity of the charge carriers, goes through a maximum, and then declines again at very high wavenumbers. Net amplification can be obtained when the maximum gain induced by the semiconductor exceeds the total loss (which is primarily due to relaxation of the ferrite magnetic moment). If the film thickness is large compared to the wavelength, the threshold condition is primarily a requirement upon the power dissipated per unit volume of semiconductor. In the converse case it is primarily a requirement upon the current per unit width of the semiconductor film. For a device using YIG (ΔHk/4πM = 2×10 -4) and InSb (mobility = 5×104 cm2/V sec) at room temperature, a film thickness of 3000 Å, and a frequency of 3 GHz, the calculated threshold power and current densities are respectively 2.5×106 W/cm3 and 2.2 A/cm. © 1969 The American Institute of Physics.