Function Of Injection Energy Research Articles

Structures and energies of small carbon clusters: what experiment and theory have to say about C +8, C +9 and C +10

The structure and energies of linear and monocyclic carbon cluster cations C + n (8 ⩽ n ⩽ 10) have been investigated using gas phase ion chromatography experiments and ab initio calculations. Cluster ions are either produced directly in the ion source by laser ablation of graphite or by collision induced dissociation of larger clusters. The relative amount of linear and cyclic isomer was determined as a function of injection energy in the drift cell. Both linear and cyclic clusters are observed at all injection energies. Using simple kinetic arguments, the cyclic isomer is shown to be lower in energy than the linear cluster ion for n = 8,9 and 10. The stability of the cyclic ion relative to the linear isomer is estimated to be 23 ± 8 kcal mol −1 for C + 8, 17 ± 8 kcal mol −1 for C + 9 and 47 ± 8 kcal mol −1 for C + 10. Restricted open shell ab initio calculations are in very good agreement with these numbers.

Negative absolute conductivity in quantum wires

The effect of negative absolute conductivity in quasi-one-dimensional quantum wire structures is obtained by the Monte Carlo simulation. This negative conductivity is associated with inelastic optical phonon scattering leading to an asymmetric electron distribution function established under conditions of intensive electron photoinjection. Simulation results suggest that quantum wires are ideal for the experimental observation of negative absolute conductivity. The oscillations of photoconductivity as a function of injection energy can reveal the spectrum of optical phonons in quantum wires which differs considerably from that in bulk materials.

Transport in submicron devices

We have studied the effects of realistic band structures on transport through the active region of hot electron transistor (HET) alloy semiconductor devices. The relevant physical parameters are the injection-energy dependence of the group velocities and the velocity scattering rates due to longitudinal optical phonons, ionized impurities, alloy disorder, and other electrons. All III–V and II–VI semiconductors and their alloys have been examined, with special emphasis placed on those showing the most promise, which are GaAs, InAs, InP, GaInAs, and InAsP. The relevant parameters are then related to device upper cut-off frequencies, the fraction of ballistic electrons, and the α-current gain parameter (the ratio of the collector to emitter current). For devices thicker than 500 Å, GaInAs alloys are demonstrated to exhibit distinct advantages. However, for thin devices (≅ 100 Å), the cut-off frequencies range around 15 THz, and no material has an appreciably higher ballistic-electron fraction than GaAs. Moreover, we have calculated the α-current gain parameter as a function of injection energy in an HET device and find agreement with the important measured features with no adjustable parameters. One new element in this theory is a simple direct calculation of the deformation potential for intervalley scattering.