Hot Electron Propagation Research Articles

Propagation of hot electrons through high-density plasmas.

Propagation of hot electrons through high-density plasmas generated by femtosecond laser pulses is investigated using three types of target configurations: Al-coated glass, Al and glass separated by a vacuum gap, and Al foil alone. Collimated ionization tracks lasting for 60 ps and extending 150-300 microm in length and 8 microm in cross section are observed via optical probing. For the Al-foil-alone target, a narrow plasma jet is formed at the rear surface in line with the laser. The collimation of the hot electrons may be attributed to a strong self-generated magnetic field in the target.

Hydrodynamical Modeling of Charge Carrier Transport in Semiconductors

Enhanced functional integration in modern electron devices requires an accurate modeling of energy transport in semiconductors in order to describe high-field phenomena such as hot electron propagation, impact ionization and heat generation in the bulk material. The standard drift-diffusion models cannot cope with high-field phenomena because they do not comprise energy as a dynamical variable. Furthermore for many applications in optoelectronics one needs to describe the transient interaction of electromagnetic radiation with carriers in complex semiconductor materials and since the characteristic times are of order of the electron momentum or energy flux relaxation times, some higher moments of the distribution function must be necessarily involved. Therefore these phenomena cannot be described within the framework of the drift-diffusion equations (which are valid only in the quasi-stationary limit). Therefore generalizations of the drift-diffusion equations have been sought which would incorporate energy as a dynamical variable and also would not be restricted to quasi-stationary situations. These models are loosely speaking called hydrodynamical models. One of the earliest hydrodynamical models currently used in applications was originally put forward by Blotekjaer [1] and subsequently investigated by Baccarani and Wordeman [2] and by other authors [3]. Eventually other models have also been investigated, some including also non-parabolic effects [4–6, 8–20]. Most of the implemented hydrodynamical models suffer from serious theoretical drawbacks due to the ad hoc treatment of the closure problem (lacking a physically convincing motivation) and the modeling of the production terms (usually assumed to be of the relaxation type and this, as we shall see, leads to serious inconsistencies with the Onsager reciprocity relations). In these lectures we present a general overview of the theory underlying hydrodynamical models. In particular we investigate in depth both the closure problem and the modeling of the production terms and present a recently introduced approach based on the maximum entropy principle (physically set in the framework of extended thermodynamics [21, 22]). The considerations and the results reported in the paper are exclusively concerned with silicon.

Measurement of Return Current in a Laser-Produced Plasma

A laser-fusion target's support fiber is heated at large distances from the laser plasma principally by Ohmic heating due to an electrical return current. Optical and electrical measurements demonstrate that return-current heating dominates over other heating mechanics such as hot-electron propagation along the fiber, thermal conduction, and line-of-sight plasma radiation.