Acoustic Deformation Potential Research Articles

Monte Carlo simulation of hot electrons in InAlAs/InGaAs heterojunctions

Monte Carlo simulation was carried out to investigate two dimensional hot electron transport in In 0.52Al 0.48As/In 0.53Ga 0.47As single heterostructure at 77 K, where scattering processes due to alloy disorder potential and two modes of LO phonons are taken into account in addition to acoustic deformation potential, ionized impurity, nonpolar optical phonon, and intervalley phonon scatterings. We discuss the importance of the conduction band nonparabolicity. The coupling constants of electron-LO phonons (two types of LO phonons) are determined from the magnetophonon resonance experiments in bulk InGaAs and the alloy disorder potential is estimated from the analysis of low field Hall mobility. We investigated the effects of the Γ-L valley energy separation and alloy disorder potential on the high field drift velocity. It is found that the alloy disorder scattering reduces the drift velocity, and that negative differential mobility depends on the energy separation between Γ and L valleys, indicating that the intervalley scattering plays an important role in the hot electron transport in the heterostructures. The maximum drift velocity ranges from 1.8 to 2.7 × 10 7 cm/s depending on the alloy disorder potential (1.1 to 0.5 eV). We also investigated the drift velocity overshoot and found that the maximum overshoot velocity is about 6 × 10 7 cm/s.

Acoustic deformation potentials in AIB

From the analysis of the variation of the energy gap with temperature and pressure in some ${A}^{\mathrm{I}{B}^{\mathrm{III}{C}_{2}^{\mathrm{VI}}}}$ chalcopyrite compounds, valence- and conduction-band acoustic deformation potentials are calculated. It is found that both the valence- and conduction-band extrema move to higher energies on compression in these compounds. This should explain the small band-gap pressure and temperature coefficients observed in ${A}^{\mathrm{I}{B}^{\mathrm{III}}}$${C}_{2}^{\mathrm{VI}}$ chalcopyrite compounds relative to their binary analogs.

Dynamical conductivity of a quantum-wire superlattice.

The dynamical current response of a multiple-quantum-wire superlattice to a time-oscillatory external electric field is examined using Kubo's linear-response theory. Couplings of the quasi-one-dimensional electron gases with phonons (polar optic, and acoustic deformation potential) are discussed to lowest order in terms of a current-current correlation function which embodies both intrawire and interwire electron-electron Coulomb interactions. The associated dynamic screening of the electron-phonon interaction is approximated by employing the random-phase-approximation density-density correlation function for the interacting electrons of the quantum-wire superlattice. The frequency-dependent conductivity of this system is evaluated numerically, exhibiting its variations with temperature and geometrical superlattice parameters.

A calculation of the phonon-drag thermopower of a 1D electron gas

The theory of phonon-drag thermopower Sg is given for a quasi-1D electron gas in a GaAs heterostructure. The coupling of the electrons to 3D phonons is considered through acoustic deformation potential and piezoelectric fields. An expression for Sg is given which may be used for quasi-1D wires of different geometries. Numerical results are presented for both the screened and the unscreened value of Sg for cylindrical wires in the temperature range 1-10 K. For temperatures T>or=2 K the major contribution to Sg comes from the deformation potential scattering but for T<2 K the contribution to Sg due to piezoelectric scattering is significant. Screening reduces Sg by 40%. Sg increases as the density of electrons decreases and curves of Sg/T3 against T show maxima. The overall behaviour is dominated by the 3D character of the phonon system and is similar to that found previously for a quasi-2D electron gas coupled to 3D phonons.

Compensation ratios in high-purity InP using an improved Hall measurement technique

Temperature-dependent Hall measurements were conducted on several high-purity n-type InP epitaxial layers grown by metalorganic chemical vapor deposition with the aim of clarifying the relationship between the 77-K Hall mobility, the free-carrier concentration, and the compensation ratio in high-purity InP. An improved method of Hall analysis for high-purity epitaxial layers was used which greatly reduces errors associated with depletion effects, as well as those associated with interfacial inhomogeneities in the growth direction. The method is essentially a modified version of the differential profiling method in which the difference between two successive Hall measurements, one before, and one after a controlled etch, is used to infer the properties of the portion of the epilayer removed during the etch. From curve fitting of the neutrality equation to the results of the temperature-dependent Hall measurements, the compensation ratios were estimated and compared to estimates obtained from previously reported calculations of the 77-K Hall mobility. The results are found to agree well with recently reported calculations for which the acoustic deformation potential and piezoelectric constant were assumed to be 6.5 eV and 0.01, respectively.

Acoustical deformation potential and effective mass in n-type lead telluride between 4 and 300 K

The acoustical deformation potential value is deduced for n-PbTe from low temperature electron mobility results. The value obtained is  = (22±2)eV. Assuming  independent of temperature T, the electron density of states effective mass at the conduction band edge follows the linear relation m ∗( T) = 0.040 m 0[1 + (4.7 ± 0.3) × 10 −3 T] between 4 and 300 K.

Low-field galvanomagnetic transport at an n-AlGaAs/GaAs heterojunction: I. Analysis

An analysis is presented for computing the low-field galvanomagnetic coefficients of the quasi-two-dimensional electron gas confined to the GaAs side of a modulation-doped AlGaAs/GaAs heterostructure. The model of confinement uses Ando's prescription for band bending and a variational wavefunction, with modification for finite-depletion regions in the active and doped layers, and with provision for a spacer layer. The method for solving the Boltzmann equation is based on the accurate numerical procedure developed for polar bulk semiconductors, namely expansion of the distribution function in degrees of anisotropy and in powers of the electric and magnetic field strengths, followed by iterative solution of the resulting coupled difference equations for the departures of the distribution from equilibrium. Analytic expressions are given for the rates of lattice scattering by acoustic deformation potential and piezo-electric mechanisms and by the polar optical mechanism, and for impurity scattering by both background and remote ionised impurities. The degeneracy of the electron distribution has been taken into account, as well as some effects of carrier screening and nonparabolicity of the bands. The predictions of this analysis for a realistic heterostructure are reported in the accompanying paper.

Acoustic deformation potentials and heterostructure band offsets in semiconductors.

It is argued that the absolute hydrostatic deformation potentials recently calculated for tetrahedral semiconductors with the linear muffin-tin-orbital method must be screened by the dielectric response of the material before using them to calculate electron-phonon interaction. This screening can be estimated by using the midpoint of an average dielectric gap evaluated at special (Baldereschi) points of the band structure. This dielectric midgap energy (DME) is related to the charge-neutrality point introduced by Tejedor and Flores, and also by Tersoff, to evaluate band offsets in heterojunctions and Schottky-barrier heights. We tabulate band offsets obtained with this method for several heterojunctions and compare them with other experimental and theoretical results. The DME’s are tabulated and compared with those of Tersoff’s charge-neutrality points.

The Deformation Potential Constant of the Conduction Band in InSb

The electron mobility in InSb has been measured at 77-380 K using the van der Pauw method. The experimental values were compared with the theoretical values obtained by an iteration technique. In the intrinsic region (T>250 K), the theoretical values were found to agree with the experimental values if the acoustic deformation potential constant, E1 was chosen to be 14 eV.

Maximum finite-temperature mobility in heterostructures: Influence of screening of electron-acoustic phonon interactions

A calculation of the phonon-limited mobility of electrons in the quasi-two-dimensional channel of AlGaAs/GaAs heterostructures has been performed over the temperature range 10–300 K. The acoustic phonon interactions are screened by the electrons in the channel and the subband structure is accounted for completely. Comparison with experiments in high-mobility samples shows that an acoustic deformation potential of more than about 12 eV is irreconcilable with the measured mobilities at intermediate temperatures.

Acoustic and Optical Deformation Potentials in Cubic IV‐VI Compounds

AbstractAcoustic and optical deformation potentials (DP) in cubic IV‐VI compounds are calculated by diagonalizing the p‐model Hamiltonian including finite lattice distortions at the L‐ and T‐points of the Brillouin zone. A very pronounced and even non‐monotonous dependence is found of some DP upon the very lattice deformation and, most surprisingly, Ξ2(L) &lt; 0 for the optical DP. This may explain the wide variance of experimental data for different samples and experimental conditions.

Acoustic phonon generation in the picosecond dynamics of dense electron-hole plasmas in InGaAsP films

Oscillations superposed on transient transmission and reflection from submicron films of InGaAsP (Eg=0.96 eV) and GaAs excited by subpicosecond optical pulses have been observed. The oscillations are due to coherent acoustic phonon generation in the thin films. Values for the velocity of sound, and the band-gap variation due to hydrostatic pressure and the difference in acoustic deformation potentials between conduction and valence bands are determined by analyzing the period and magnitude of the oscillations.

Structure and Bonding in Cubic IV–VI Crystals VI. Acoustic and Optical Deformation Potentials

AbstractWithin the six‐band p‐model by Volkov et al. the acoustic and optical deformation potentials for the band‐edge states at the L‐points of the Brillouin zone are derived. Numerical results are obtained by means of geometrical arguments and chemical trends of tight‐binding parameters. These agree well with experimental and other theoretical results for the optical deformation potentials, but not for the acoustic ones. The conclusion in II on the smallness of the average interband‐optical deformation potentials is confirmed.

Hot-electron galvanomagnetic conduction in n-InSb at 77 K.

The Monte Carlo (MC) method is used to analyze high-field Hall-effect measurements on n-InSb at 77 K in a magnetic field of 5 mT. The Hall factor, the Hall mobility, and the drift mobility are calculated as a function of the electric field. A nonparabolic conduction band is used and polar LO-phonon, acoustical-phonon, and ionized impurity scattering are incorporated in the MC calculations. The acoustical deformation potential is determined from the high-electric-field (Eg150 V/cm) mobility. Good agreement with experiment is found for an acoustical deformation potential between 18 and 30 eV. The impurity concentration is then determined from the low-field mobility results.

Low field mobility of 2-d electron gas in modulation doped AlxGa1−xAs/GaAs layers

We derive a simple analytical formula for the low field electron mobility which uses the 2-d degenerate statistics of the 2-d electron gas. This takes into account the finite width of the depletion layer in (Al,Ga)As for the scattering by remote donors, scattering by the interface charge, and the polar-optical and acoustic deformation potential and piezoelectric scattering. The largest measured value of mobility is determined by scattering due to interface charge in some cases. The ultimate value of the mobility which may be achieved is limited by the acoustic deformation potential and piezoelectric scattering at about 6.5×106 cm2/V s for an interface carrier density of the 2-d electron gas ns0 ≂4×1011 cm−2. Our results agree very well with experimental data obtained in our laboratory as well as other laboratories.

Alloy scattering potential in p-type Ga1−xAlxAs

The two-band transport model is expanded in order to analyze the Hall mobility of p-type III–V compound semiconductors. Using this model, the drift and the Hall mobilities can be calculated separately. The alloy scattering as an additional scattering mechanism in alloy semiconductor systems is assumed and the Hall mobility of p-type Ga1−xAlxAs is analyzed. By comparing the theoretically calculated Hall mobility with the reported Hall mobility data of high purity p-GaAs, the acoustic phonon deformation potential and the optical phonon deformation potential were found to be 7.0 and 11.5 eV, respectively. Theoretical calculations showed that the acoustic and nonpolar optical phonon scattering are more prominent than the polar optical phonon scattering at 300 K in the entire Al compositional range. The alloy scattering potential was determined comparing the theoretically calculated values with the Hall mobility of liquid phase epitaxial p-type Ga1−xAlxAs. Best agreement in the compositional variation at room temperature and the temperature variation was found with the alloy scattering potential of 0.7 eV.

Quantum corrections to conductivity and energy relaxation in InP and InSb

We present results on conduction in the metallic impurity band of InP at low temperatures. Below 4 K, in zero magnetic field, we observe a T12 correction to the conductivity consistent with the Coulomb interaction model, although the sign of the change is not in agreement with theory. The observation of a negative magneto-resistance also indicates the rôle of localization in the conduction process and we have attempted to separate the two mechanisms by measuring for both ωcτ<1 and ωcτ > 1.We have measured the energy relaxation time in InSb for various electron and lattice temperatures. The results are discussed in terms of energy loss via acoustic piezoelectric, deformation potential and polar optical scattering. We have measured the electronic specific heat on the insulating side of transition and find it is consistent with a small density of states, but not a gap.

Theory of free-electron optical absorption in n-InSb.

Theory of free-electron absorption in InSb-type narrow gap semiconductors is developed and used to describe experimental data for n-InSb. Electron-two-phonon interaction is shown to give negligible contribution to absorption, while plasmon generation is an important absorption mechanism. Good agreement between the theory and experiment is obtained for acoustic deformation potential C = -14.6 eV.

Electron mobility in the X conduction band minima of Ga1−xAlxAs alloys

Hall Mobility of the electrons in the indirect energy X conduction band minima of Ga1− xAlxAs alloys (0.23≤ x≤ 0.78) has been measured as a function of temperature (T≤ 300K). For alloys (0.23≤ x≤ 0.32) investigated with the direct energy band gap, the band structure has been inverted with the application of the hydrostatic pressure to make the X states considerably lower in energy than the next higher energy minima. For indirect energy- gap alloys (0.61≤ x ≤ 0.78) investigated, the mobility has been measured at atmospheric pressure. The acoustic deformation potential, longitudinal optical phenon temperature and the inter-valley deformation potential field for the X minima have been derived from the experimental results, and are found to increase with the alloy composition. A single valley density of states mass with best value of 0.35 mo with three equivalent X minima situated at the zone edge, are required to fit the data. It has been concluded that the various parameters involved in the alloy and space charge scatterings in the alloys, except the electros mass, do not change with pressure and that the intervalley scatter-ing plays an important role in limiting the electron mobility in. the alloys at a pressure and composition near the Γ- L cross- over.

Acoustic deformation potential interaction in the two-polaron problem

The ground-state energy of two deeply bound acoustic deformation potential (ADP) polarons is examined as a function of the separation between them. A detailed interrelation between the ground-state energy of the system and the size and the structure of the ADP polaron is exhibited. It is also observed that the equilibrium separation is not altered by any variation of the strength of phonon coupling and the values of the band masses.