Two mechanisms of negative dynamic conductivity and generation of oscillations in field-emissions structures

There is great interest in the generation and amplification of high-frequency oscillations and their use in vacuum microelectronic devices. The main advantages of such devices are radiation hardness and reduced switching times due to electron transport in vacuum. In this presentation two proposed mechanisms for the generation of high-frequency oscillations are investigated and analysed. The first mechanism is connected with the generation of oscillations in field emission structures based on silicon (or metal) tips with multilayer film coatings. Several types of silicon-based structures are investigated, namely silicon tips coated with multilayer films including a Si delta-doped layer (Si.SiO2.Si.SiO2) and coated with ultrathin (<10 nm) diamond-like carbon (DLC) films. Theoretical calculations have shown possibilities of resonant tunnelling in the electron transport mechanism through such coatings when electron field (FE) emission takes place. The current-voltage characteristics of a FE with negative differential conductivity are experimentally observed. Estimations suggest the possibility of generation of oscillations with frequencies between 200 MHz and 100 THz in such structures. The second mechanism is based on direct generation of oscillations in GaAs Gunn cathodes with emission to an anode. GaAs vertical and lateral electrodes have been produced and investigated. Oscillation in the current-voltage characteristics was observed. In this case there is no limitation related to transit-time effects in the input region; this is because the emitted electrons are not under the influence of an oscillating electric field