Theory of the hot free carrier intraband-absorption coefficient of n-inversion layers

The absorption coefficient K of a quasi two dimensional (2D) hot free electron gas is calculated for the first time as a function of the lattice temperature T, the photon angular frequency w, the carrier density N_s as well as the electron temperature T_e when the carriers are scattered by ionized impurities, acoustic phonons and polar optical phonons. Analytical expressions are derived in the limiting cases of non-degeneracy and degeneracy of the electron system. In the quantum limit ħw/k_BT_e ≳ 1 where the interaction between the electron and the photon is inelastic K sensitively depends on the limiting scattering mechanism showing that the electron motion is completely controlled by the photon field. In the classical limit ħw/k_BT_e ⪡ 1 the absorption decreases proportional to w¹ independent of the limiting scattering mechanism in agreement with the experimental data deduced from far-infrared absorptivity measurements on GaAs heterolayers.     

Remote polar phonon scattering for hot electrons in Si-inversion layers

The effect of the remote interfacial phonon (R.I.P.) scattering on the carrier drift velocity v is evaluated in function of the effective mobility, i.e. in function of the surface roughness. A perturbation theory using the experimental ν?F relation as a zero order approximation is used to calculate the contribution of the R.I.P. scattering. The calculation shows that the influence of this phonon mode scattering on the transport properties in Si-inversion layers is dependent on the carrier low field mobility and is of the order of 10%. The R.I.P. scattering is particularly significant in the warm electron regime, having no consequence on the saturation velocity.     

Theory of atomic spectral emission intensity

The theoretical derivation of a new spectral line intensity formula for atomic radiative emission is presented. The theory is based on first principles of quantum physics, electrodynamics, and statistical physics. Quantum rules lead to revision of the conventional principle of local thermal equilibrium of matter and radiation. Study of electrodynamics suggests absence of spectral emission from fractions of the numbers of atoms and ions in a plasma due to radiative inhibition caused by electromagnetic force fields. Statistical probability methods are extended by the statement: A macroscopic physical system develops in the most probable of all conceivable ways consistent with the constraining conditions for the system. The crucial role of statistical physics in transforming quantum logic into common sense logic is stressed. The theory is strongly supported by experimental evidence.     

Theory of the input power-dependence of the electron heating in n-inversion layers

The average energy loss P of hot electrons due to the interaction with acoustic bulk phonons is calculated and used to determine the electron heating temperature Δ as a function of the input power eμE². It is found that P creases proportional to Δ² and is independent of the carrier concentration. Consequently the ratio Δ/√ eμE² turns out to be a constant $\text{(0.75 × 10}{}^{\mathrm{?2}}\text{K/(eV/s)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ for $\text{n-Si and 2.04 × 10}{}^{\mathrm{?2}}\text{K/(eV/s)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ for n-GaAs) in agreement with the experimental data deduced from FIR-emission experiments at T = 4.2 K.     

Luminescence from hot electrons relaxing by LO phonon emission in p-GaAs and GaAs doping superlattices

Laser excited hot electrons in GaAs relax by LO phonon emission within a few hundred femtoseconds, leading to a series of peaks in the distribution of hot electrons in the conduction band, which we observe in luminescence. We find that the luminescence peaks shift according to the acceptor binding energy for C?, Ge?, Zn?, and Be-p-doped GaAs layers grown by MBE and LPE. Thus we prove that recombination is between hot electrons and neutral acceptors. The series of peaks due to electrons from the heavy hole band agree well with $\text{k}\text{.}\text{p}$ band structure, while peaks due to those from light holes are about 15 meV lower than expected from the band structure. We show that the discrepancy is not due to heating or surface fields. The peak separation in the luminescence ladder is about 6% larger than the LO energy suggesting emission of renormalised LO phonons. We find thermalisation by LO emission also in GaAs nipi doping superlattices. In nipi crystals the emission is shifted to higher energies (by 12 meV for light and by 6 meV for heavy holes) due to a change in band structure caused by the space charge fields.     

Hot electrons in nonparabolic bands with acoustic and polar optical phonon scattering

Most compound semiconductors have nonparabolic energy bands, and in pure material the dominant scattering mechanisms are usually by acoustic and polar optical phonons. In this paper, general expressions for the high-field transport properties of such materials are derived, using the balance-of-energy method and assuming a drifted Maxwellian distribution function. Under certain conditions the resultant drift velocity-field curves show a single-band negative differential resistance, arising not only from the increase in effective mass with carrier energy, but also from the change in relative scattering efficiencies of the two mechanisms as the applied field is increased. This effect is more marked at low temperatures. The model gives good agreement with previously reported experimental results on n-type PbTe at 77°K.     

The emission of electrons from hot silicon surfaces

The emission of electrons from hot silicon surfaces is reviewed in an effort to present a summary of the state of research in this field. The theoretical aspect of the problem is outlined briefly, and experimental results covering the temperature and field dependence of the saturation current density, as well as the anisotropy and the energy distribution of the emission are presented.     

Probing phonon emission via hot carrier transport in suspended graphitic multilayers

We study hot carrier transport under magnetic fields up to 15 T in suspended graphitic multilayers through differential conductance () spectroscopy. Distinct high-energy anomalies have been observed and shown to be related to intrinsic phonon-emission processes in graphite. The evolution of such anomalies under magnetic fields is further understood as a consequence of inter-Landau level cyclotron-phonon resonance scattering. The observed magneto-phonon effects not only shed light on the physical mechanisms responsible for high-current transport in graphitic systems, but also offer new perspectives for optimizing performance in graphitic nano-electronic devices.     

Anisotropic and polarized intraband light emission of hot electrons

Far infrared luminescence of hot electrons in InSb have been studied. The emission probabilities derived in the second order perturbation are obtained for different scattering mechanisms: acoustic phonons, optical phonons and impurities. The origin of anisotropy and polarization of the light emission due to anisotropy of the electron distribution function under the electric field is described theoretically and calculated using the Monte Carlo method. The theoretical conclusions are confirmed by the experiment.     

Energy losses of 2D electron gas due to near-surface acoustic phonon scattering

We have shown that for quantum wells placed close to the stress-free surface of the semiconductor heterostructure, the energy relaxation rate of two-dimensional electrons interacting with acoustic phonons at low temperatures (Bloch–Grüneisen regime) is changed considerably in comparison with that of a two-dimensional electron gas placed in a bulk of semiconductor. The relaxation rate is enhanced in the case of a semiconductor–vacuum system and is suppressed in the case of the surface covered by a thin metal film. The enhanced energy loss is caused by additional scattering at localized and reflected acoustic waves, and the decrease appears due to suppression of piezoelectric scattering in the vicinity of the metal.     

Monte Carlo simulation of two-dimensional hot electrons in n-type Si inversion layers

Monte Carlo simulation is carried out to study high field transport of the two-dimensional electron gas formed on the (100) surface of silicon. Good agreement is obtained between the measured and calculated results. The saturation of the drift velocity is found to depend on the magnitude of the first-order intervalley phonon scattering.     

Theory of weak ion acoustic double layers

We present a theory of small amplitude ion acoustic double layers in a homogeneous unmagnetized plasma. Using fluid equations for ions and a general equation of state for electrons, we show that such double layers exist when the free and reflected electron distributions are different from maxwellians.     

激光功率密度对Al膜靶后表面快电子发射的影响

 报道了在20 TW皮秒激光器上完成的p偏振激光与等离子体相互作用过程中产生的快电子的角分布和能谱测量结果。实验得到：当激光功率密度小于10¹⁷ W/cm²时,电子发射没有明显定向性,在激光入射面内多峰发射;当激光功率密度大于10¹⁷ W/cm2,小于10¹⁸ W/cm²时,电子主要沿靶面法线方向发射;当激光功率密度达到相对论强度时,电子主要沿激光传播方向发射;激光功率密度未达到相对论强度时,靶后表面法线方向快电子能谱拟合平均温度符合共振吸收温度定标率;激光功率密度达相对论强度以上时,靶后表面法线方向快电子能谱拟合平均温度高于已有的温度定标率。     

近相对论强度激光与薄膜靶相互作用中靶厚度对超热电子发射方向的影响

研究了近相对论强度的激光脉冲与薄膜靶相互作用中，靶厚度对超热电子发射方向的影响.实验发现，随着靶厚度的增加，靶后超热电子的发射方向向靶的法线方向移动，同时电子束的发散角变大.结果分析表明，靶背面电荷分离场强度的变化是影响电子发射方向的主要原因. 关键词： 飞秒激光脉冲 超热电子 靶厚度     

Theory of weak modified electron acoustic double layers

Summary We have obtained the double-layer solutions for the small-amplitude modified electron acoustic waves propagating in a plasma having one ion and two electron components. No DLs solutions are found to exist when the temperature of the free and trapped particles is considered to be the same for all the species. However, when the effects of the reflected hot electrons are considered, DL solutions are found to exist.

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Riassunto Si sono ottenute soluzioni del doppio strato per onde acustiche modificate dall’elettrone di piccola ampiezza, che si propagano in un plasma avente una componente ionica e 2 componenti elettroniche. Si trova che non esistono soluzioni DL quando la temperatura delle particelle libere e intrappolate si considera stessa per tutte le specie. Tuttavia si trova che le soluzioni DL esistono quando si considerano gli effetti degli elettroni caldi riflessi.

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Резюме Мы получили решения для двойных слоев в случае акустических волн с малой амплитудой, распространяющихся в плазме, имеющей одну ионную и две электронные компоненты. Показано, что не существуют решения для двойных слоев, когда температура свободных и захваченных частиц является одинаковой для всех компонент. Однако, когда учитывается влияние отраженных горячих электронов, решения для двойных слоев существуют.

     

Theory of intensity noise in semiconductor laser emission

The intensity fluctuations expected in the output of cw semiconductor lasers are studied analytically using linearized multimode rate equations. Spontaneous emission causes intrinsic fluctuations of the laser wave. A power-independent contribution to the intensity fluctuations may occur due to inversion-induced modulation noise. The correlation of the low-frequency noise of different laser modes is investigated. The results are in agreement with experimental data reported in the literature.     

Effects of laser intensity on the emission direction of fast electrons in laser-solid interactions

The dependence of emission direction of fast electrons on the laser intensity has been investigated. The experimental results show that, at nonrelativistic laser intensities, the emission of fast electrons is mainly in the polarization plane. With the increase of the laser intensity, fast electrons emit towards the laser propagation direction from laser polarization direction. At relativistic laser intensities, fast electrons move away from the laser polarization plane, closely to the reflection direction of the incident laser beam.