Analysis of inelastic scattering of quasi-two-dimensional electrons of a superlattice by acoustic phonons with allowance made for the miniband dispersion

Formulas for the effective momentum-relaxation time and mobility of quasi-two-dimensional electrons of a superlattice with consideration of inelastic scattering by acoustic phonons and the dispersion of the miniband energy spectrum as a function of the longitudinal wave vector have been obtained. Numerical calculation was performed for a nondegenerate gas of quasi-2D electrons in a symmetrical GaAs/Al_0.36Ga_0.64As superlattice with a quantum well width of 5 nm at T=77 K. It was shown that consideration of the elasticity of scattering and the dispersion of the miniband energy spectrum gives rise to a significant increase in the electron mobility.     

Interaction of an acoustic wave with electrons drifting in crossed electric and magnetic fields in InSb

Experimental results are reported for the piezoelectric interaction of a u.h.f. acoustic wave with electrons drifting in crossed d.c. electric and magnetic fields in ntype InSb at 77°K. Electronic amplification of the acoustic wave was observed.     

Electron scattering from acoustic phonons in quantum dots and other nanostructures

Scattering of electrons from acoustic phonons in semiconductor nanostructures occurs via an interaction, which we call the “ripple mechanism”, in addition to the usual deformation potential coupling. We provide a general derivation of this novel coupling mechanism and give detailed expressions for it which are valid for all nanostructure systems, including those with quasi-zero-, one- and two-dimensional geometries. Calculations are presented here of the electron scattering rates due to acoustic phonons for quantum dots in a variety of shapes. We find that scattering due to the ripple mechanism dominates that from the deformation potential for dot sizes less than 50 nm and that the ripple mechanism contribution can be much larger for smaller dot sizes.     

Mean energy of photoexcited hot electrons in high magnetic fields

Several authors have determined the mean energy of a photoexcited electron gas in the absence of magnetic field. Assuming a Maxwellian distribution for the electrons, they used the power balance equation to find the electron temperature T_e. Noting that when a strong magnetic field is applied, the electron collision integral vanishes in the extreme quantum limit, we derive a theoretical expression for T_e using a similar approach. Recombination and various scattering processes by optical and acoustical phonons are considered and the dependence of T_e on magnetic field, lattice temperature and laser excitation freqeuency is studied.     

Energy relaxation of photoexcited hot electrons at very low temperatures

The scattering of electrons with energy $\text{?<}\text{1}\text{2}\text{ms}{}^2$ by acoustical phonons at very low temperatures T?ms² is investigated.     

A quasi-classical description of the conductivity oscillations in layered crystals under the condition of charge-carrier scattering by acoustic phonons

The oscillating part of the longitudinal conductivity of layered crystals is considered within the quasi-classical approximation, where both the electric field and quantizing magnetic field are perpendicular to the layers. Our approach differs from the conventional one by taking into account both the nonparabolicity of a narrow conduction miniband and the dependence of the Fermi surface size in the direction of the magnetic field on charge-carrier concentration. This approach makes it possible to consider not only the standard case, with open Fermi surfaces, but also the case of closed Fermi surfaces. It is shown that, for closed Fermi surfaces, the existence of frequencies that do not correspond to extreme cross sections of the Fermi surfaces cut by planes normal to the magnetic field can serve as a criterion for the narrowness of the conduction miniband, which determines the translational motion of charge carriers across the layers.     

Drift velocity of electrons in quantum wells in high electric fields

It is experimentally found that the maximum drift velocity of electrons in quantum wells of differently arranged AlGaAs/GaAs heterostructures and pseudoamorphous Al_0.36Ga_0.64As/In_0.15Ga_0.85 As heterostructures is higher than the maximum drift velocity of electrons in bulk materials. It is established that no negative differential conductivity is exhibited by the field dependence of the drift velocity of two-dimensional electrons in GaAs and In_0.15Ga_0.85As. The drift velocity in the GaAs quantum well is saturated in fields several times higher than the field corresponding to the Γ-L intervalley transitions of electrons in bulk GaAs.     

Resonant raman scattering and dispersion of polar optical and acoustic phonons in hexagonal inn

It is shown that a study of the dependence of impurity-related resonant first-order Raman scattering on the frequency of excitation light makes it possible to observe the dispersion of polar optical and acoustic branches of vibrational spectrum in hexagonal InN within a wide range of wave vectors. It is established that the wave vectors of excited phonons are uniquely related to the energy of excitation photon. Frequencies of longitudinal optical phonons E₁(LO) and A₁(LO) in hexagonal InN were measured in the range of excitation-photon energies from 2.81 to 1.17 eV and the frequencies of longitudinal acoustic phonons were measured in the range 2.81–1.83 eV of excitation-photon energies. The obtained dependences made it possible to extrapolate the dispersion of phonons A₁(LO) and E₁(LO) to as far as the point Γ in the Brillouin zone and estimate the center-band energies of these phonons (these energies have not been uniquely determined so far).     

Transport of electrons in a GaAs quantum well in high electric fields

The rates of intrasubband and intersubband scattering of electrons by polar optical and intervalley phonons are determined in relation to the electron energy and width of a deep rectangular quantum well in GaAs. The Monte Carlo method was used to calculate the field dependences of the electron’s drift velocity in quantum wells with the width of 10, 20, and 30 nm. It is shown that the drift velocity in high electric fields in a quantum well vastly exceeds the maximum drift’s saturation velocity in the bulk material.     

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)     

Tunneling emission of electrons from semiconductors’ valence bands in high electric fields

Tunneling emission currents of electrons from semiconductors to vacuum (needle-shaped GaAs photodetectors) and to a metal (silicon metal-insulator-semiconductor diodes with a tunneling-transparent insulator layer) are studied in high and ultrahigh electric fields. It is shown that, in semiconductors with the n-type conductivity, the major contribution to the emission current is made by the tunneling emission of electrons from the valence band of the semiconductor, rather than from the conduction band.     

Amplification of radiation in the far infrared range by hot holes in germanium in crossed electric and magnetic fields

The results of direct gain measurements are reported for the amplification of polarized and unpolarized, long-wavelength, infrared radiation by hot holes in germanium in crossed electric and magnetic fields in the Voigt and Faraday configurations. The experimental data are compared with gain calculations. Fiz. Tekh. Poluprovodn. 31, 1482–1486 (December 1997)     

Scattering of electrons by confined interface polar optical phonons in a double-barrier heterostructure

It is shown that capture of the surface (interface) phonons can occur in a double-barrier heterostructure in addition to the capture of bulk polar optical phonons. The strength of interaction of electrons with confined interface phonons becomes lower as the thickness of the phonon well (a semiconductor layer where phonons are captured) is decreased. A new approach is suggested for reducing the scattering of electrons by polar optical phonons in a double-barrier quantum well; this approach is based on separate capture of phonons in narrow phonon wells. The calculated scattering rate with the capture of interface phonons into the GaAs/InAs/GaAs and AlAs/GaAs/AlAs quantum wells taken into account is found to be much lower than the rate obtained in the approximation of scattering of electrons by bulk phonons. A multifold decrease in the rate of electron-phonon scattering in the AlAs/GaAs/AlAs quantum well is obtained by separating this well by the monomolecular InAs layer that is transparent for electrons but acts as a reflecting barrier for polar optical phonons.     

Interaction of electrons with optical phonons localized in a quantum well

The scattering rate of electrons in a quantum well by localized polar optical and interface phonons is considered. The dependence of the force of the electron-phonon interaction on the frequency of optical phonons in materials of the heterostructure forming the electron and phonon quantum wells is determined. It is shown that, by varying the composition of semiconductors forming the quantum well and its barriers, it is possible to vary the scattering rates of electrons by a factor of several times. The scattering rates of electrons by polar optical phonons are calculated depending on the fractions In _x and In _y in the composition of semiconductors forming the In _x Al_{1 ? x} As/In _y Ga_{1 ? y} As quantum wells. Dependences of the mobility and saturated drift velocity of electrons in high electric fields and quantum wells In _y Ga_{1 ? y} As on the composition of the In _x Al_{1 ? x} As barriers introduced into quantum wells are determined experimentally. The electron mobility increases, while the saturated drift velocity decreases as the fraction of In _x in the composition of barriers is increased.     

The longitudinal diffusion coefficient and the mobility of hot electrons in silicon

The longitudinal diffusion coefficient of electrons in silicon is (i) calculated as a function of electric field strength from noise and current measurements on a n⁺nn⁺ planar silicon device and (ii) measured vs field strength with the help of the Time-of-Flight technique at 200, 160 and 77 K.The electric field was oriented along the 〈111〉 direction. The first method yielded results for fields lower than 10⁵ Vm^?1 whereas the second method yielded results for fields ranging from 2 × 10⁴ to 2 × 10⁶ Vm^?1. Values for the mobility obtained with the first method are presented as well and compared with Time-of-Flight data.     

Reciprocal drag of electrons and phonons in strongly doped HgFeSe semiconductors

The previously observed unusual dependences of the thermoelectric and thermomagnetic coefficients of strongly doped HgFeSe crystals on temperature and magnetic field intensity are studied theoretically. It is shown that the observed dependences are due to the combined effect of electron scattering by spatially correlated charged donors Fe(3+) at low temperatures and the reciprocal drag of electrons and phonons, which plays a large role in semiconductors with a high density of itinerant charge carriers. Fiz. Tekh. Poluprovodn. 33, 701–707 (June 1999)     

Experimental corrections for the hot hole distribution function in germanium in crossed electric and magnetic fields

A procedure for finding corrections for the hot hole distribution functions obtained from absorption measurements on intersubband transitions of hot heavy and light holes in germanium in crossed electric and magnetic fields is proposed. This procedure is based on the multiple-valued dependence of the absorption on the photon energies of transitions from light holes to a subband split off as a result of the spin-orbit interaction. Taking these corrections into account improves the agreement between the gain for direct optical transitions between the light and heavy hole subbands calculated from measurements of the absorption in the near-infrared and direct measurements in the far-infrared. Fiz. Tekh. Poluprovodn. 32, 1197–1199 (October 1998)     

Tunnel emission of electrons in photo-field detectors and in an auger transistor in very strong electric fields

The effect of a strong electric field [(5–7)×10⁷ V cm^?1] on the electron emission from a semiconductor to vacuum in photo-field detectors and in MIS structures with a tunnel-transparent insulator layer (Al-SiO₂-n-Si Auger transistor) has been studied. It is shown for the first time that the existence of deep self-consistent quantum wells on the semiconductor surface in a strong electric field provides a possibility of controlling the energy of fast electrons responsible for the impact ionization near the base of the Auger transistor and changes the photosensitivity of narrow-gap photo-field cathodes in the IR spectral range due to the formation of a transistor structure at the semiconductor-vacuum interface. It is also demonstrated that, both in photo-field detectors and in tunnel Al-SiO₂-n-Si transistor structures, only the electron tunnel current should be taken into account and the hole current, disregarded. The reason for this is that only the electron current exists in vacuum, and the tunneling of holes in Al-SiO₂-n-Si from the semiconductor into the metal is unlikely because of the large hole effective mass in the valence band of SiO₂.     

An empirical pseudopotential-based description of carrier scattering by LO phonons in semiconductor heterostructures

We have developed a model of LO phonon scattering in semiconductor heterostructures using the solutions of strained-layer empirical pseudopotential calculations with Fermi's Golden Rule. We have utilised this model to perform quantitative calculations of scattering lifetimes in GaSb/InAs photodetector superlattices over a temperature range of 50-400 K. The temperature dependencies of phonon absorption and emission by carriers are identified and the physical mechanisms behind these are traced. Comparisons with earlier calculations on elastic scattering due to isovalent defects are made. Phonon emission is found to be the dominant effect in most cases, exhibiting the shortest lifetimes and hence the largest scattering rates. These lifetimes are in the picosecond regime and are in good agreement with more widespread, envelope function-based calculations of phonon lifetimes in semiconductor heterostructures.