Abstract
The theory of hot electrons injection in carbon nanotubes (CNTs) where both dc electric field (Ez), and a quasi-static ac field exist simultaneously (i.e. when the frequency ω of ac field is much less than the scattering frequency v (ω⪡v or ωτ⪡1, v=τ−1) where τ is relaxation time) is studied. The investigation is done theoretically by solving semi-classical Boltzmann transport equation with and without the presence of the hot electrons source to derive the current densities. Plots of the normalized current density versus dc field (Ez) applied along the axis of the CNTs in the presence and absence of hot electrons reveal ohmic conductivity initially and finally negative differential conductivity (NDC) provided ωτ⪡1 (i.e. quasi- static case). With strong enough axial injection of the hot electrons, there is a switch from NDC to positive differential conductivity (PDC) about Ez≥75kV/cm and Ez≥140kV/cm for a zigzag CNT and an armchair CNT respectively. Thus, the most important tough problem for NDC region which is the space charge instabilities can be suppressed due to the switch from the NDC behaviour to the PDC behaviour predicting a potential generation of terahertz radiations whose applications are relevance in current-day technology, industry, and research.
Highlights
Carbon nanotubes (CNTs) [1] - [3] are subject of many theoretical [4] - [9], and experimental [10] - [18] studies
We probe the behaviour of the electric current density of the CNTs as a function of the applied dc field E of ac − dc driven fields when the frequency of ac field (ω) is much less than the scattering frequency (v) (ω v or ωτ 1 i.e quasi-static case [31], where v = τ −1) with and without the axial injection of the hot electrons
4e2γ0/√3nh2(ac as a function of the applied dc field E when frequency of ac field ω is much less than scattering frequency v(ω v or ωτ 1 i.e. quasi-static case) for the CNTs stimulated axially with the hot electrons, represented by the nonequilibrium parameter η in figure 1
Summary
The most important tough problem for NDC region which is the space charge instabilities can be suppressed due to the switch from the NDC behaviour to the PDC behaviour predicting a potential generation of terahertz radiations whose applications are relevance in current-day technology, industry, and research
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