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A simple miniature source generating pulse trains with a central frequency of ∼100 GHz and a duration of 50–100 ps has been demonstrated recently. The source is based on nanometer-scale collapsing field domains (CFDs) generated in the collector of an avalanching bipolar GaAs transistor. The central frequency is determined by the domain transient time across the collector, and thus, a routine increase in the oscillation frequency from 0.1 to 0.3–0.5 THz would require a reduction in the collector thickness by a factor of 3–5. This is not acceptable, however, since it would reduce the maximum blocking voltage affecting the achievable peak current across the avalanche switch. We suggest here a solution to this challenging problem by reducing the CFD travel distance while keeping the collector thickness unchanged. Here, the discovered and interpreted phenomenon of CFD collapse when entering a dense carrier plasma zone made it possible by means of bandgap engineering. A CFD emitter generating ∼200 GHz wavetrains of ∼100 ps in duration is demonstrated. This finding opens an avenue for the increase in the oscillation frequency without any reduction in the emitted power, by using a smart structure design.