ACOUSTOELECTRIC AMPLIFICATION AT MICROWAVE FREQUENCIES IN INSB IN CROSSED ELECTRIC AND MAGNETIC FIELDS

Acoustic amplification of 52 dB has been observed with shear waves propagating in the frequency range 1-1·5 GHz in InSb at 77°K in crossed electric and magnetic fields. The amplification was linearly dependent on the drift field for 0<E<5 v cm-1, but for electric fields greater than 5 v cm-1 the gain tended towards saturation. Amplification was also observed with a one-port system, where the coherent acoustic signal was amplified over two transit times, the drift-field polarity being reversed immediately after one transit time. In this case a maximum electronic gain of 74 dB was observed. The same technique used over four transit times gave an electronic gain of 112 dB which corresponded to 8 dB net gain. An incoherent noise instability was observed in both the one- and two-port amplifier and was dependent on both fields being applied. The maximum noise level in the one-port amplifier, as detected on a narrow-band receiver, was -63 dB m, as compared with -67 dB m for the two-port amplifier. This resulted in a net improvement in the signal-to-noise ratio of approximately 20 dB in the one-port system as compared with the two-port. The zero-fields attenuation was measured at 77°K and was 12 dB cm-1 at 1 GHz, increasing to 15 dB cm-1 at 1·7 GHz.