Showing papers on "Effective mass (solid-state physics) published in 1982"

Material parameters of In1−xGaxAsyP1−y and related binaries

Abstract: Various models for calculation of physical parameters in compound alloys are discussed and the results for In1−x Gax Asy P1−y quaternaries are presented. The model used is based on a linear interpolation scheme, and therefore necessitates known values of the parameters for the related binary and ternary alloys. The material parameters considered in the present study can be classified into the following eleven groups: (1) lattice constant and crystal density, (2) thermal expansion coefficient, (3) electronic‐band structure, (4) external perturbation effect on the lowest‐direct gap, (5) effective mass, (6) dielectric constant, (7) Frohlich coupling parameter, (8) elastic properties, (9) piezoelectric properties, (10) deformation potential, and (11) excitonic effect. Of particular interest is the deviation of material parameters from linearity with respect to the alloy composition. It is found that the present model provides generally acceptable parameters, in good agreement with the existing experimental da...

On tunneling in metal‐oxide‐silicon structures

Abstract: The analysis of Fowler‐Nordheim tunneling data in metal‐oxide‐silicon structures is reviewed. It is concluded that a parabolic dispersion relation for SiO2 and an electron effective mass of mox = 0.5m provide the best description of the experimental results, this conclusion is consistent with recent band structure calculations for SiO2. Also included is a brief discussion of the transverse momentum conservation issue for tunneling from silicon of 〈100〉, 〈110〉, and 〈111〉 orientation into SiO2.

Compositional dependence of band‐gap energy and conduction‐band effective mass of In1−x−yGaxAlyAs lattice matched to InP

Abstract: The band‐gap energy and the electron effective mass of In1−x−yGaxAlyAs lattice matched to InP have been determined as a function of Al content. From photoluminescence measurements we obtain Eg(eV) = (0.76±0.04)+(1.04±0.10)y+(0.87±0.13)y2. The electron effective mass is determined from the plasma frequencies measured with Raman scattering in n‐type samples. Its compositional dependence is given by m* = (0.0427±0.0015)+(0.0683±0.0007)y.

A GaAsxP1−x/GaP strained‐layer superlattice

Abstract: Strained−layer superlattices form a broad new class of semiconductor materials with tailorable electronic properties. We have succeeded in growing a GaAsxP1−x/GaP(100) strained−layer superlattice (SLS). The structure was grown by alternate metalorganic chemical vapor deposition of thin (60 A)layers (20 each) of GaAs0.4P0.6 and GaP. These layers were grown onto a GaAsxP1−x layer which was graded in composition from x = 0 (composition of underlying GaP substrate)to x = 0 (average composition of the SLS). Photoluminescense studies of the SLS were carried out to determine the optical band gap. At T = 78 K, the spectrum shows a dominant band−edge peak at 2.03 eV as well as weaker peaks at higher energies. Tight binding and effective mass calculations, also carried out, predict a direct band gap (due to zone folding) of 2.02 eV and higher lying transition energies which are in good agreement with these data.

Intrinsic density ni (T) in GaAs: Deduced from band gap and effective mass parameters and derived independently from Cr acceptor capture and emission coefficients

Abstract: Prior attempts at determination of the intrinsic density in GaAs are reviewed, and this quantity is then deduced anew from the temperature dependences of the intrinsic gap and of the valence and conduction band system statistical weights. The nonparabolicity of the lowest conduction band, and the effects of the next two conduction bands, are taken into account in deducing ni (T) for the range 250–1500 K. That procedure gives a room‐temperature value ni (300) = 2.1×106 cm−3, which can be compared with prior values from various experimental methods. The magnitude and temperature dependence of ni are then calculated by a different and entirely new method, which utilizes experimental data of the electron and hole emission and capture coefficients associated with Cr2+?Cr3+ transitions of the substitutional CrGa deep‐level impurity in GaAs. Recent data of Martin et al. concerning these coefficients permits a deduction of ni(T) = 1.05 ×1016 T3/2 exp(−0.802/kT) cm−3 for 300

Photoluminescence study of acceptors in AlxGa1−xAs

Abstract: A photoluminescence study of C, Si, Ge, Be, Mg, and Zn acceptors in AlxGa1−xAs is made. The binding energy of these acceptors is determined from the free‐to‐bound transitions at 75 K as a function of aluminum composition up to x∼0.4. It is observed that C, Be, and Mg behave like effective mass acceptors in AlxGa1−xAs while Si, Zn, and Ge show positive deviations from the effective mass theory with Ge exhibiting the maximum deviation. This difference in the behavior of the acceptors is suggested to be due to the difference in their central cell corrections in GaAs. The relative merits of these acceptors, in terms of their solubility, ionization energy, and diffusivity are considered. It is concluded that Mg is an attractive acceptor dopant in AlxGa1−xAs grown by liquid phase epitaxy.

Two-Dimensional Plasma Resonances in Positive Ions under the Surface of Liquid Helium.

Abstract: Plasma resonances have been observed in a two-dimensional sheet of positive ions held just under the surface of liquid $^{4}\mathrm{He}$ The ion effective mass deduced from the resonant frequencies is found to be weakly temperature dependent, increasing linearly with temperature Strong nonlinear effects are observed in the wave propagation The ponderomotive force of the plasma wave induces a static $2k$ distortion of the charge density, which produces large shifts of the resonant frequency with drive amplitude

Spectral functions and hole nuclear states

Abstract: An explicit expression for the spectral function of hole nuclear states is given in the framework of the coherent fluctuation model. It is shown that the spectral function and single-particle width, centroid energy, quasiparticle effective mass, etc., are functionals of the ground-state nucleon density distribution. Calculation of the spectral functions for58Ni,40Ca,28Si is carried out and the results are compared with the experimental data.

Zero Sound, Spin Fluctuations, and Effective Mass in Liquid 3 He

Abstract: The coupling of density and spin-density fluctuations to the single-particle excitations in $^{3}\mathrm{He}$ at zero temperature is studied. The present results exhibit a sharply peaked effective mass close to the Fermi surface, caused by the attractive quasiparticle interaction in the spin-1 particle-hole channel. The coupling to the zero-sound mode causes a secondary maximum around $2{k}_{\mathrm{F}}$. This mechanism can reconcile the rapid variation of the specific heat with a well-defined zero-sound mode at large momenta.

A de Haas-van Alphen study of the field dependence of the Fermi surface in ZrZn2

Abstract: Pulsed field de Haas-van Alphen measurements of the Gamma centred part of the Fermi surface in ZrZn2 are presented for fields up to 35T. The spin-split Fermi surface was found to be field dependent. It is argued that the observed de Haas-van Alphen frequency is different from the frequency defined by the Onsager relation. An expression is derived based on the Stoner-Wohlfarth model which describes the difference in spin-up and spin-down frequencies as a function of field strength. The observed difference in the effective mass for the two spin directions can also be explained by this model and it compares well with band structure calculations. An anomalous behaviour of the second harmonic of the majority surface de Haas-van Alphen frequency was observed. A search for other frequencies was carried out but in spite of the high sensitivity, in terms of m*TD, no other orbits were seen.

Energy dependence of the effective mass in liquid3He

Abstract: The striking behavior of the specific heat of liquid3He as function of temperature at low temperatures requires the effective massm* to change rapidly with temperature; this can be translated into a rapid variation with energy,m*/m dropping from itsE=0 value to ∼1 over the temperature range ≲0.5 K. We explore this effect in a model in which the enhancement of the effective mass is due to coupling to spin fluctuations. At very lowT≲50 mK, the variation in specific heat results fromT3 lnT terms. The free energy, on the other hand, does not containT2 lnT terms in its dependence on the magnetic field, implying that the susceptibility, which is essentiallym*/(1+F0a), also does not have such logarithmic terms. Consequently, ifm* varies with energy, so mustF0a, so as to leave the susceptibility free of this rapid variation. The rough constancy ofm*/(1+F0a) seems empirically to hold to higher energies and temperatures. Ifm*/m drops, with increasing energy, to unity, the spin-fluctuation theory, which is described in terms of Landau parameters at the Fermi surface, goes over into the paramagnon theory. The rapid change with energy of the effective interactions can be understood within the framework of response theory as a “shaking off” of the relevant collective modes with increasing frequency of the imposed oscillations. The changes in effective interactions have consequences for the interpretation of experiments involving inelastic neutron scattering from liquid3He.

Effect of size quantization on the effective mass in ultrathin films of n-Cd 3 As 2

Abstract: An attempt is made to investigate the effects of size quantization on the effective mass in ultrathin films ofn-Cd3As2. It is found that the effective mass at the Fermi level depends on the size quantum number due to the effect of crystal-field splitting, resulting in different effective masses at the Fermi level corresponding to different electric subbands. It is also observed that the different effective masses closely approach each other, for a given film thickness, with increasing electron concentration and, for a given electron concentration, with increasing film thickness.

On the interface connection rules for effective‐mass wave functions at an abrupt heterojunction between two semiconductors with different effective mass

Abstract: The problem of the connection rules for effective‐mass wave functions across an abrupt heterojunction is investigated by expressing the results of a one‐dimensional, tight‐binding approximation in terms of effective‐mass wave functions. It is shown that the widely used conventional connection rules of continuous wave function and slope break down if the effective masses on the two sides are different, except if a certain interface matrix element happens to equal the geometric mean of two analogous bulk matrix elements, a case referred to as χ normal. In this case the conventional connection rules yield correct energy eigenvalues, but the effective‐mass wave functions themselves differ from true probability amplitudes by a factor depending on the local effective mass, different on the two sides. Heterojunctions that deviate from χ normality may, to the first order, be described as if a δ‐function potential had been added at the interface.

Interaction Effects on the Zeeman Splitting of Collective Modes in Superfluid He 3 - B

Abstract: Exact calculations of the $B$-phase collective-mode frequencies in a magnetic field are presented, and they provide new information about the effective mass, the pairing interaction, and the Landau parameters. The calculation of the Zeeman splitting for the 2+ mode (real squashing mode) is consistent with the zero-field frequency and agrees quantitatively with the measurements of Avenel et al., for a range of values of ${m}^{*}$ which includes some, but not all, of the differing experimental results for this important parameter.

Temperature-dependent effective mass of a self-trapped electron on the surface of a liquid-helium film

Abstract: We have used the Feynman path-integral formulation of the polaron problem to compute the temperature-dependent effective mass of a two-dimensional electron on a film of liquid helium for values of the coupling constant from weak to strong. Because of the nature of the ripplon spectrum (very low velocities) we find that the self-trapped structure (found at $T=0$) "melts" for rather small $\frac{\mathrm{kT}}{{E}_{B}}$. Here ${E}_{B}$ is the zero-temperature binding of the localized state.

Defect-induced tunnelling and the conductivity of strongly disordered systems

Abstract: For a model describing the motion of a zero-temperature electron gas in an environment causing a fluctuating potential and a fluctuating effective mass, a theory is developed which allows for an approximate calculation of the particle density propagation self-consistently with momentum relaxation and defect-induced tunnelling processes. All correlation functions of the system are expressed in terms of two causal kernels for which non-linear equations are derived and solved. A detailed discussion of the influence of the defect-induced tunnelling on the mobility, in particular on mobility edges, and on the Fermi glass stiffness is given and an anomalous high-frequency tail of the dynamical conductivity is predicted.

Ballistic transport in semiconductors

Abstract: The ballistic transport approximation in semiconductors is considered, in light of recent calculations which show that the accuracy of this approximation is improved when the mass appropriate to this effect is enhanced over the normal effective mass. We show that this enhancement is a consequence of the presence of scattering even on the very short time scale.

Resonant Brillouin Scattering of Exciton Polaritons in 2H-PbI 2

Abstract: Resonant Brillouin scattering spectra are measured on a layer semiconductor 2H–PbI 2 . The observed exciton polariton dispersion in the direction parallel to the c -axis is interpreted by a two branch polariton model yielding the translational exciton mass of 2.3 m 0 and the effective dielectric constant of 10. The anisotropy of the effective mass is estimated to be m // / m ⊥ =3.4 for exciton and 4.4 for conduction electron, respectively.