Surface carrier wave amplification in InSb at X-band

Experiments have been conducted with slabs (1.5 × 2.5 × 0.3 mm³) of n-InSb to determine the propagation of surface waves in the presence of drifting carriers. Interdigital transducers of 10 fingers each with finger width of 7.5 µ (periodicity 30 µ) are used to excite slow surface waves with phase velocity on the order of the electron drift velocity of 2 × 10⁷cm/s. Integrated coplanar strip lines are used to carry to and from the transducers to X-band waveguides at each end. A nonsaturable unidirectional electronic gain of 11 dB/mm has been observed in the presence of counterstreaming electron-hole plasma created under pulsed high fields and a transverse magnetic field of 10 kG. The experimental results are explained on the basis of a surface plasma wave propagation model including the surface properties of the material through the surface recombination velocity. Rougher surfaces are shown to result in enhanced interaction but suffer from the susceptibility to oscillations. Reasonably well prepared but not exceptionally smooth surfaces are found to be better from the point of view of stable amplification.