Nonlinear terahertz gain estimated from multiphoton-assisted tunneling in resonant tunneling diodes

The power-dependent terahertz (THz) gain due to subband transitions between adjacent quantum wells is estimated from the current change of triple-barr ier resonant tunneling diodes (RTDs) under THz irradiation. To induce high THz voltage across the RTDs, patch antennas with low conduction loss are in tegrated. Due to high THz voltages induced, photon-assisted tunneling by th e multiphoton process is observed. Components of tunneling currents with ph oton emission and absorption are extracted from the observed results, and t he gain coefficient in the multiphoton process is estimated. It is shown th at the gain coefficient is almost constant for incident power in the low in cident power region in which one- or two-photon processes are dominant, and starts to rapidly decrease when the incident power exceeds this region. Re asonable agreement with theoretical calculation is obtained.