Inelastic scattering of hot electrons by neutral donors in heavily silicon-doped GaAs/AlAs quantum wells

The energy and momentum relaxation of hot electrons in n-type GaAs/AlAs quantum wells is studied. Hot photoluminescence due to the recombination of hot electrons with holes bound on Si acceptors is observed in structures with a high level of doping with silicon. Using the method of magnetic depolarization of hot photoluminescence, the probability of scattering of hot electrons is found to decrease substantially with increasing temperature in the range 4–80 K. This effect is shown to be due to the ionization of donors. It is established that the probability of inelastic scattering by neutral donors is several times greater than the probability of quasielastic electron-electron scattering. Fiz. Tekh. Poluprovodn. 33, 1235–1239 (October 1999)     

Quantitative measurements of intervalley and carrier-carrier scattering in GaAs with hot (e,A) luminescence

We have used photoluminescence from nonequilibrium electrons recombining at neutral acceptors to quantitatively measure hot electron kinetics in GaAs. Values have been obtained for intervalley scattering rates as a function of electron kinetic energy and the scattering rate of a single nonequilibrium electron in the presence of a sea of thermalized carriers. These measurements demonstrate the power of this new probe of nonequilibrium carrier relaxation in direct gap semiconductors.     

The problem of intermediate temperatures or electric fields in the scattering of hot electrons by acoustic phonons

An approximate expression is derived for the momentum relaxation time in the quasielastic scattering of hot electrons by acoustic phonons as a function of the electron energy and the lattice temperature. The mobility and the dependence of the impurity breakdown electric field on the degree of compensation are calculated in the electron-temperature approximation. The results of the calculations are in good agreement with the experimental for n-type Ge. Fiz. Tekh. Poluprovodn. 31, 1071–1073 (September 1997)     

Changes in the luminescent and electrical properties of InGaN/AlGaN/GaN light-emitting diodes during extended operation

Changes in the luminescence spectra and current-voltage and capacitance-voltage characteristics of light-emitting diodes based on InGaN/AlGaN/GaN heterostructures were investigated as functions of operating time during extended use. Sample blue and green light-emitting diodes with InGaN single quantum-well active layers were examined during operating times of 10²−2×10³ h at currents up to 80 mA. An increase in the efficiency at the working currents (15 mA) was observed in the first stage of aging (100–800 h) followed by a decrease in the second stage. The greatest changes in the spectra were observed at low currents (<0.15 mA). Studies of the distribution of charged acceptors in the space-charge region showed that their concentration grows in the first stage and falls in the second. Models explaining the two stages of aging are proposed: 1) activation of Mg acceptors as a result of destruction of residual Mg-H complexes, and 2) formation of N donor vacancies. A model of subthreshold defect formation by hot electrons injected into the quantum wells is discussed. Fiz. Tekh. Poluprovodn. 33, 224–232 (February 1999)     

Monte Carlo simulation of the low-temperature mobility of two-dimensional electrons in a silicon inversion layer

The transport of two-dimensional electrons in a silicon inversion layer is determined by Monte Carlo simulation in the temperature range 4.2–40 K, where the electrical quantum limit occurs and only the lowest subband is populated. Two scattering mechanisms are taken into account: scattering by distant ionized impurities and scattering by surface roughness elements, along with their dependence on the polarizability of the two-dimensional electron gas. The mobility and coefficient of warm electrons in weak electric fields are calculated. The data are compared with previously published results. Fiz. Tekh. Poluprovodn. 31, 89–92 (January 1997)     

Mechanisms of excitation of the f-f emission in silicon codoped with erbium and oxygen

The Er₂O₃ cluster in silicon is discussed as a possible source of the Er-related emission in Si:Er, O. We propose a mechanism that gives a simple explanation of the high efficiency of Er atom excitation in Er-O clusters. The cases of photoluminescence and electroluminescence are considered. In the case of photoluminescence the high efficiency of Er excitation is attributed to the electron state localized at the Er-O cluster. The excitation of f-shell electrons in Er atoms occurs via the Auger recombination of the exciton bound at the Er-O cluster. We calculate the rate of this Auger process and discuss the dependence of the photoluminescence intensity on the carrier concentration. In the case of electroluminescence under reverse bias the impact excitation cross section is enhanced due to resonant scattering of the hot electrons at the quasi-discrete levels formed by the Er-O cluster quantum-well potential. The calculated impact excitation cross section is close to the experimental value. Fiz. Tekh. Poluprovodn. 33, 664–670 (June 1999) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

Momentum relaxation time and temperature dependence of electron mobility in semiconductor superlattices consisting of weakly interacting quantum wells

Formulas are derived for the longitudinal and transverse electron momentum relaxation times in a superlattice consisting of weakly interacting quantum wells in the approximation of a bulk-semiconductor scattering potential. Scattering by impurity ions, neutral atoms, and volume-type longitudinal acoustic and polar optical phonons is studied. A numerical analysis is performed of the longitudinal and transverse momentum relaxation times for scattering by impurity ions and neutral atoms as a function of the electron energy, temperature, density of the electron gas, and quantum well width. Fiz. Tekh. Poluprovodn. 33, 1240–1245 (October 1999)     

Trapping of hot electrons at repulsive centers under transverse runaway conditions

The trapping of hot electrons at repulsive centers under transverse runaway conditions is calculated. The dependence of the trapping probability on the Sommerfeld factor and the exponential dependence of the trapping probability on the energy of the tunneled electron are taken into account. It is shown that the latter dependence plays an important role near the threshold of transverse runaway of hot electrons, while far from the threshold the Bonch-Bruevich trapping probability is a good approximation. Fiz. Tekh. Poluprovodn. 31, 268–270 (February 1997)     

Effect of impurities with variable valency on the transport phenomena in a quantum well

Transport phenomena in a quantum well containing a multivalent impurity are investigated on the basis of a model of strong Coulomb correlations. It is shown that as the iron content in the quantum well increases, the Coulomb correlations grow and produce ordering in the impurity system. As a result, the scattering of 2d electrons by them should weaken, and this should result in a substantial increase in the mobility of 2d electrons. Fiz. Tekh. Poluprovodn. 31, 769–773 (April 1997)     

IGFET hot electron emission model

A new model for hot electron emission into the oxide layer of IGFETs is presented. When IGFETs operate under high gate and drain bias conditions, electrons are accelerated by the high drain field and injected into the oxide layer at a certain probability. The present model takes into account the following: (1) the energy dependence of hot electron scattering probability, (2) the three-dimensional angle at which electrons are injected into the oxide layer, (3) the quantum effect at the SiSiO₂ interface that gives the reflection probability, and (4) the scattering and reaching probabilities without energy loss. The total emission current is obtained by a five-fold integral over the energy, position and solid angle elements. The current thus predicted is expected to be two or three orders of magnitude smaller than that from Phillips' model previously proposed for IGFET emission current and hence closer to experimintal data. The present model can give the position dependence of emitted current and is suitable for incorporation into two-dimensional numerical analysis.     

Where do hot electrons come from? [MOSFETs]

Troublesome hot electrons that are appearing in MOSFETs, even at reduced drain voltages, due to scattering in the device channel are discussed. The use of the concept of `electron temperature' to describe the energy spread that the electrons have as the result of the scattering is examined. The relationship between electron temperature and reliability is considered. The improvement in reliability that results from reducing the channel length, and thereby the amount of scattering, is discussed. The analysis of short-channel devices, is briefly addressed     

Electron transport and ionization in silicon at high fields

The saturated drift velocity measured for electrons at high fields is inconsistent with Shockley's model for impact ionization in silicon. It is explained in terms of a field-dependent mean free path for high energy phonon creation in the electric field direction, electrons creating a high energy phonon as soon as they have acquired sufficient energy from the field. Assuming that the electron wavepacket travels at the saturated drift velocity without dispersion, it can be shown that the increased scattering rate at high fields must result in a large spread in the carrier energy. If a drifted Maxwellian distribution is assumed, a unique expression can be obtained for the carrier temperature T^* which is in good agreement with the measured field dependence of the ionization coefficient. In this model, a cylindrical hot carrier distribution must be assumed with the hot carrier energy in a plane perpendicular to the applied field. Exact calculations of the magneto-resistance of such a distribution can be made verifying that the drift velocity is indeed saturated.     

Interplay between the hot phonon effect and intervalley scattering on the cooling rate of hot carriers in GaAs and InP

The influence of hot phonon effect and intervalley scattering on the hot carrier cooling rate was investigated using femtosecond time‐resolved photoluminescence spectroscopy in bulk GaAs and InP, two electronically similar but vibrationally distinct semiconductors. In both materials, a broad photoluminescence signal that extends from the band gap energy to values larger than the pump pulse energy was observed during the first few picoseconds after photoexcitation, for different excitation energies (1.7, 1.88, and 2.4 eV) at high carrier densities (>10¹⁹ cm⁻³). Different hot carrier relaxation times were observed in GaAs and InP for different excitation energies, demonstrating the influence of intervalley scattering phenomena in GaAs. When electrons were not energetic enough to access satellite valleys, longer decay transients were observed for InP compared with GaAs. This provides experimental evidence of the hot phonon effect in InP. Temperature transients were calculated by analyzing the topography of the two‐dimensional spectra. Copyright © 2011 John Wiley & Sons, Ltd.     

Mechanism of erbium electroluminescence in hydrogenated amorph silicon

The mechanism of the electroluminescence of erbium under a reverse bias in structures based on hydrogenated amorphous silicon is studied. Erbium ions are excited through an Auger process, in which conduction electrons are trapped by neutral dangling bonds (D ⁰ centers) located near the erbium ions. A stationary current through the structure is sustained by a reverse process involving the thermally stimulated tunneling emission of electrons by negatively charged dangling-bond defects (D ⁰ centers) into the conduction band of the amorphous matrix. Fiz. Tekh. Poluprovodn. 33, 671–673 (June 1999)     

Conductivity and photoconductivity of polymeric composites containing heteropolynuclear Cu(II)/Mn(II) complex in the presence of ionic polymethine dyes

Electrical and photoconductive properties of polymeric composites doped with heteropolynuclear Cu(II)/Mn(II) complex were studied in comparison with copper acetate and manganese oxalate. In the visible region, the internal photoelectric effect is enhanced by doping with organic polymethine dyes (capable of photogenerating the holes or electrons), as well as with donors or acceptors that provide carrier transport in a neutral polymeric binder. It was assumed that there are states for carrier recombination on the surface of heteropolynuclear complex particles.     

Radiative recombination in modulation-doped GaAs/AlGaAs heterostructures in the presence of an electric field

The radiative recombination processes involving two dimensional (2D) carriers from the notch potential formed at the interface of modulation doped GaAs/AlGaAs heterostructures have been studied by means of photoluminescence (PL) and photoluminescence excitation spectroscopy in the presence of an external electric field applied perpendicular to the layers via a gate electrode. Two PL bands related to the 2D electron gas are interpreted as the radiative recombination between 2D electrons and holes from the valence band (HB1) and from residual acceptors (HB2), respectively. The band bending in the active layer, which determines the energy positions of these H-bands, can be controlled by applying an external electric field. However, also the separation between the Fermi edge, E_F, and the second 2D electron subband is deliberately varied by applying an electric field. At a sufficiently small separation, an efficient scattering path near k=0 is available for electrons at the Fermi energy. This can be observed in the PL spectra as a striking enhancement of the many-body excitonic transition, usually referred to as the Fermi edge singularity (FES). The enhancement of the FES is usually explained in terms of an efficient scattering for electrons at the Fermi edge via the nearly resonant adjacent subband. The efficiency of this process is dependent on the separation between the Fermi edge, E_F, and the next subband, which can be controlled via the applied field in our experiments.     

Calculation of the trapping of hot electrons by repulsive centers under the conditions of a needle-type distribution function

The trapping coefficient of hot electrons repelled by a Coulomb center is calculated explicitly for a needle-shaped electron distribution function under conditions where the effective trapping cross section, along with the Sommerfeld factor, depends exponentially on the energy of the electron which has tunneled through the barrier. The criteria under which the effective Bonch-Bruevich cross section is valid are obtained. Fiz. Tekh. Poluprovodn. 31, 944–946 (August 1997)     

Electrons and phonons in quantum wells

The modulation of electron and polar optical phonon states in an AlGaAs/GaAs/AlGaAs quantum well (QW) with an inserted thin AlAs barrier is considered. The OW width dependence of electron-phonon scattering rates are estimated. The large contribution to the change of the electron subband population, the photovoltaic effect, and the electron mobility in the QW accounts for the resonant intersubband scattering of electrons by interface phonons. The decrease of electron mobility limited by polar optical phonon scattering with increasing carrier concentration in the QW is established. The conditions for the increase of mobility in the QW by inserting the AlAs barrier are found. Fiz. Tekh. Poluprovodn. 33, 1049–1053 (September 1999) This article was published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

Determination of the LO-phonon and Γ→L intervalley scattering time in GaAs from hot electron luminescence spectroscopy

Both the LO-phonon scattering time and the Γ→L intervalley scattering time for electrons in the conduction band of GaAs are of fundamental importance, and they are needed for the modelling of devices. We measure the steady state distribution of hot electrons in lightly p-doped bulk GaAs under carrier densities of 10¹³–10¹⁴cm⁻³, which is orders of magnitude lower than in pulsed laser experiments. Using a 16×16 k.p Hamiltonian and taking into account the transition matrix elements in a dipole model, we determine the hot electron lifetime from comparison with the experimentally found lifetime broadening. For electrons with a kinetic energy of 100meV to 300meV we obtain τ_LO=(132±10)fs. We also determine the Γ→L intervalley separation as E_ΓL=(300±10)meV. We find Γ→L scattering times around 150fs to 200fs, corresponding to a value for the associated deformation potential of D_ΓL=(9.4±1.5)×10⁸eV/cm.     

Theoretical investigation on thermal effect in organic semiconductors

Thermal effect on a neutral and a doped polymer chain is studied in the frame work of Su–Schrieffer–Heeger tight-binding model considering electronic Fermi–Dirac distribution as well as atomic square-random distribution. It is found that in a neutral polymer chain, the band gap is decreasing as the temperature increases. For a doped polymer chain, extra electrons will occupy high energy levels. The localization and stability of the electronic self-trapped state will decrease with temperature. We also show that at temperature high enough (⩾340 K in present parameters), a hot electron will get rid of the trap of the lattice and become extended over the whole polymer molecule. In addition, the effects of the quantity of charge carriers and the electron–phonon coupling at room temperature are also investigated.