Indium phosphide microwave oscillators

A detailed examination has been carried out on the characteristics of transferred electron microwave oscillators constructed from epitaxial indium phosphide. Seven slices have been used, for which the layer thicknesses varied between 5.4 and 28 µm. It is shown that the mechanism of oscillation has a transit-time dependence and that the transit velocity which emerges (1.5-2 × 10
⁷
cm/s) is approximately the same as the peak electron drift velocity. It is therefore concluded that propagating space-charge layers are responsible for the oscillations. However, in view of the high transit velocities involved, it is unlikely that the space-charge layers are well-formed dipolar domains. Despite the transit-time dependence, individual devices have been made to oscillate over very wide frequency ranges (8-28 GHz). Operation of devices at frequencies up to 40 GHz has established the high-frequency capability of the oscillators. The best pulsed results obtained have included 0.5 W, 6.3 percent at 13.8 GHz; 1.05 W, 4.2 percent at 18.0 GHz and 0.65 W, 2.6 percent at 25.0 GHz. Continuous operation of these diodes has not yet been possible due to material and thermal technology limitations.