  The Zener-Klein (ZK) interband tunneling in graphene layers (GLs) with the
lateral n-i-n and p-i-n junctions results in the nonlinear I-V characteristics
that can be used for the rectification and detection of the terahertz (THz)
signals. The transit time delay of the tunneling electrons and holes in the
depletion regions leads to the phase shift between the THz current and THz
voltage causing the negative dynamic conductance in a certain frequency range
and resulting in the so-called transit-time (TT) instability. The combination
of the ZK tunneling and the TT negative dynamic conductance enables resonant
THz detection and the amplification and generation of THz radiation. We propose
and evaluate the THz devices based on periodic cascade GL p-i-n structures
exhibiting the TT resonances (GPIN-TTDs). Such structures can serve as THz
amplifiers and, being placed in a Fabri-Perot cavity, or coupled to a THz
antenna or using a ring oscillator connection, as THz radiation sources.
