Generation of millimeter radiation due to electric-field-induced electron-transit-time resonance in indium phosphide

The stimulated millimeter radiation from $n$-type indium phosphide was observed at $T=4.2\,$ K in a strong electric field. The generation is due to the appearance of negative differential conductivity near the electron-transit-time resonance and electron bundling in momentum space in a strong electric field under conditions of low-temperature scattering from optical phonons. The dependence of the radiation frequency and intensity on the electric field was experimentally measured and the radiation spectrum is presented. The experimental data satisfactorily agree with the results of numerical simulations obtained previously by the Monte-Carlo method.