Plasma oscillations in terahertz photomixing high-electron-mobility transistor structure on p⁺-substrate

The excitation of plasma oscillations in a channel of a high-electron-mobility transistor (HEMT) induced by optical illumination for terahertz (THz) generation requires a back contact to collect photogenerated holes. In particular, it could be a heavily doped p⁺-substrate. The effect of such a substrate on plasma oscillations in the channel is considered. Both possible reasons for oscillation damping, hole collisions and heavy hole-light hole transitions, are taken into account. We show that for properly designed structures, the influence of the p⁺-substrate on plasma oscillations can be negligible.