Charge carrier scattering channels in graphite bridging its valence and conduction band offer an efficient Auger recombination dynamic to promote low energy charge carriers to higher energy states. It is of importance to answer the question whether a large number of charge carriers can be promoted to higher energy states to enhance the quantum efficiency of photodetectors. Here, we present an experimental demonstration of an effective Auger recombination process in the photo-excited nano-graphite film. The time-resolved hot carrier thermalization was analyzed based on the energy dissipation via the Auger scattering channels. We split the Auger recombination occurrence centered at 0.40 eV energy state into scattering and recombination parts, for characterizing the scattering rate in the conduction band and the recombination rate toward the valence band. The scattering time with respect to the energy state was extracted as 8 ps · eV⁻¹, while the recombination time with respect to the energy state was extracted as 24 ps · eV⁻¹. Our study indicates a 300 fs delay between the hot carrier recombination and generation, leading to a 10⁵ ps⁻¹ · cm⁻³ Auger scattering efficiency. The observed duration for the Auger recombination to generate hot carriers is prolonged for 1 ps, due to the hot carriers energy relaxation bottleneck with optical-phonons in the nano-graphite. The presented analytic expression gives valuable insights into the Auger recombination dynamic to estimate its most efficient energy regime for mid-infrared photodetection.

An efficient finite-difference time-domain (FDTD) algorithm is proposed for studying frequency- and temperature-dependent characteristics of some graphene-based structures, with auxiliary differential equation-FDTD method and its conformal modification technique integrated together for handling such atomically thin and electrically dispersive periodic geometries. Numerical results are presented to show their tunable transmittances, surface plasmon polarization-mode characteristics and Fano resonances, where the effects of chemical potential of graphene, biasing electric field strength, as well as operating temperature are captured and investigated in detail.

We study the nonlinear optical response generated by the massless Dirac quasiparticles residing around the topologically-protected Dirac/Weyl nodal points in three-dimensional (3D) topological semimetals. Analytical expressions of third-order interband nonlinear optical conductivities are obtained based on a quantum mechanical formalism which couples 3D Dirac fermions with multiple photons. Our results reveal that the massless Dirac fermions in three dimensions retains strong optical nonlinearity in terahertz frequency regime similar to the case of the two-dimensional Dirac fermions in graphene. At room temperature, the Kerr nonlinear refractive index and the harmonic generation susceptibility are found to be n₂ = 10⁻¹¹ ∼ 10⁻⁸ m²W⁻¹ and χ⁽³⁾ = 10⁻¹⁴ ∼ 10⁻⁸ m²V⁻², respectively, in the few terahertz frequency regimes, which is comparable to graphene and orders of magnitudes stronger than many nonlinear crystals. Importantly, because 3D topological Dirac/Weyl semimetals possess bulk structural advantage not found in the strictly two-dimensional graphene, greater design flexibility and improved ease-of-fabrication in terms of photonic and optoelectronic device applications can be achieved. Our finding reveals the potential of 3D topological semimetals as a viable alternative to graphene for nonlinear optics applications.

Electrothermal characterization of a metallic single-walled carbon nanotube (SWCNT) interconnect array is performed in this paper. The array is biased by a high voltage or under the impact of an electrostatic discharge pulse current. Using both time-dependent and -independent finite-difference methods, 1-D longitudinal heat conduction equation of SWCNT in the array is first solved, with CNT length-dependent temperature distribution, breakdown voltage, power handling capability, as well as transient thermal response captured and compared. Two modified equivalent electrothermal circuit models of a single SWCNT and an SWCNT array are proposed to accurately characterize hybrid effects of the biasing voltage, CNT length, and maximum rise in temperature. Their electrothermal circuit models are further implemented for investigating self-heating impact on signal integrities of SWCNT interconnect arrays, in particular, time-delay-induced crosstalk and noise. It is theoretically demonstrated that self-heating effect should be considered carefully in the design of local SWCNT interconnects when a high biasing signal voltage is applied.