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The electron delay time associated with the electron propagation across the FET gate barrier layer under high positive gate bias is expected to induce a dynamic negative differential conductance and enhance the growth of plasma waves in the channel. This dynamic negative conductance is related to the phase shift between the current and voltage waveforms caused by the electron time delay during the electron tunneling through the gate barrier. We present experimental investigations of the plasma wave detector responsivity at 200 GHz and 600 GHz radiation for long channel AlGaAs/GaAs and AlGaInN/GaN based HEMTs at 8 K and 300 K. The appearance of detector response correlated with an increase of the injected gate current under the forward gate bias is reported for both types of the investigated devices. Our results confirm that a large gate current can enhance the excitation of plasma waves.