Electronic States In Semiconductors Research Articles

Tunneling recombination in semiconductor structures with nanoscale disorder

A model of generalized generation-recombination theory is proposed for semiconductors with nanoscale disorder. Application of the developed recombination model made it possible to determine the parameters characterizing localization of electronic states in semiconductors with different atomic compositions and positional ordering. It is shown that the spatial parameters of this localization are in the nanoscale range. For this reason, the main transport factor is the tunneling of the charge carrier; the electronic transitions between the allowed bands and states in the mobility gap also play an important role. On the basis of the study performed, it is concluded that only consideration of both factors yields adequate description of the electronic processes in the structures based on semiconductors with nanoscale disorder.

Dressed-band theory for semiconductors in a high-intensity infrared laser field

Under the illumination of intense off-resonant laser light, the electronic states of semiconductors are strongly modified, or dressed, by the oscillating electric field. We present a framework using linear combination of atomic orbital band theory to calculate the dressed band structure and optical absorption spectrum of covalent semiconductors in an intense off-resonant laser field. The interaction with the laser field is taken into account exactly from the beginning of the band calculation. It is shown that the irradiation of an intense infrared laser gives rise to a blueshift of the absorption edge as well as the emergence of a new absorption band below the edge, in agreement with recent experimental data for GaAs crystals.

Temperature Dependence of the Energy Gap of Semiconductors in the Low-Temperature Limit

The temperature dependence of the electronic states and energy gaps of semiconductors is an old but still important experimental and theoretical topic. Remarkably, extant results do not clarify the asymptotic T-->0 behavior. Recent breakthroughs in the spectroscopy of enriched 28Si allow us to measure changes in the band gap over the liquid 4He temperature range with an astounding precision of one part in 10(8), revealing a T4.0+/-0.2 decrease with increasing T. This is in excellent agreement with a theoretical argument predicting an exponent of 4. This power law should apply, in the low temperature limit, to the temperature dependence of the energies of all electronic states in semiconductors and insulators.

Modulated Photocurrent Measurements On Icosahedral Quasicrystals Of AI-Pd-Re System

AbstractModulated photocurrent method originally developed for analyzing the electronic states of semiconductor has been applied to an Al-Pd-Re quasicrystal having high electrical resistivity. The measured DC component of the photocurrent has indicated that the mobility of the photocarrier is approximately the same as that of the dark carrier at the Fermi level. The data of the amplitude and phase shift of the AC component can be explained well by a simple model in which only the two processes, carrier generation and recombination, are involved. The recombination time obtained by fitting is by about six orders larger than those reported for semiconductors. The long recombination time as well as the energy independent mobility of carriers are discussed in view of a spiky structure in electron density of states expected for the quasicrystals.

Semiconductors under Uniaxial Strain

AbstractUniaxial strain, having a larger number of irreducible components, yields in principle more information than its hydrostatic counterpart. It has, however, the drawback that its magnitude is limited by sample fracture. We discuss the methods of application of uniaxial stress to solid samples for the purpose of performing spectroscopic measurements. We then present some of the highlights of such measurements, concerning phonons and electronic states in semiconductors.

Metastable transition of EL2 in GaAs: The electron-phonon-coupling channel

We propose a theoretical approach to the general problem of phonon-coupling between localised electronic states in semiconductors, which takes advantage of results from first-principles calculations. Application of this scheme to the isolated antisite defect As Ga in GaAs reveals that electron-phonon coupling can provide the mechanism for the metastable transition characteristic of EL2.

Semiconductor Pressure Sensors as Seen by a Physicist

The effect of pressure on the electronic states in semiconductors is reviewed in order to point out the phenomena useful for the pressure calibration. Specific examples are discussed in more detail: the optical sensor based on the quantum-well luminescence, the InSb resistive gauge, the AlGaAs graded-gap sensor.

A Mathematical Model for the Influence of Deep‐Level Electronic States on Photoelectrochemical Impedance Spectroscopy: II . Assessment of Characterization Methods Based on Mott‐Schottky Theory

The impact of the assumptions inherent in using the Mott‐Schottky theory to identify deep‐level electronic states in semiconductors was assessed by comparison to the results of a less restrictive mathematical model. The model, developed in another paper, treated the transport and recombination reactions involving electrons, holes, and electronic states located within the bandgap. The capacitive component used in standard Mott‐Schottky theory was found to be insensitive to bulk electronic states within the bandgap for concentrations significantly less than the doping level. The resistive component measured at low frequencies was much more sensitive to deep‐level states and may be used to determine their distribution. For high concentrations of deep‐level states, the model results were in agreement with the current practice of attributing changes in the slope of the Mott‐Schottky curve to partial ionization of single‐energy deep‐level states with applied potential. In the absence of frequency dispersion, these changes in slope could be attributed instead to nonuniform dopant distribution.

Stability of the Positions of an Interstitial Impurity Atom and the Electronic States in Semiconductors

Stability of the Positions of an Interstitial Impurity Atom and the Electronic States in Semiconductors

Calculation of semiconductor band bending due to a superficial zone including electronic states: Application to Schottky diodes

A very simple and general method for calculating band bending profiles due to electronic states in semiconductors is proposed. In the present study, states are assumed to be close to the semiconductor surface, their densities decreasing from the surface to the bulk. Two cases are considered. The first is the case of the free semiconductor surface. Some simple examples are presented in order to demonstrate that the penetration depth of the states is also an important parameter that can account for experimental behaviour. The other is the metal-semiconductor contact. Assuming Schottky-Mott interface conditions, the proposed examples show that a Schottky barrier independent of metal work function can only be obtained if the states spread far enough from the interface. The general conclusion, of particular interest for studies devoted to the interaction of semiconductor surfaces with metals or other materials, is that the fact that the states can penetrate into the semiconductor must be considered in any attempt to explain experimental results.

Capture into deep electronic states in semiconductors

This paper attempts a careful theoretical study of nonradiative electron capture by deep levels in semiconductors and has been undertaken with a view toward understanding the relevant processes, developing criteria for the choice of an appropriate set of vibronic states, and evaluating the various approximations which are commonly made in calculating capture cross sections. These points are illustrated for a specific model---a one-band, one-site potential modulated in depth by a single normal mode---which is solved numercially and in several approximations for various vibronic coupling strengths. The work establishes the following results: (1) A correct treatment of the cascade process through which energy is transferred to the lattice is essential in obtaining meaningful cross sections. In particular, the strength of cascade coupling in relation to the other scattering processes determines the number of vibronic levels which contribute effectively to capture and, thus, controls the magnitude and temperature dependence of the cross section. (2) Although "internal" scattering generated by the nonadiabatic terms in the local Hamiltonian can contribute to capture, "external" scattering by bulk lattice phonons may be more important. Further, such phonon scattering is related to the electronic transport properties of the material, and its contribution to capture can be calculated easily and accurately in the Condon approximation, although the latter fails for internal scattering. (3) The effectiveness of internal scattering is determined by the vibronic states used in the calculation, while an appropriate choice of the latter is dictated by the cascade process. The adiabatic states constitute a reasonably good choice. (4) Perturbation expressions for the electronic wave functions are completely inadequate, even for the weakest coupling, because the transition matrix elements depend upon the wave functions far from equilibrium. (5) The frequency changes generated by nonlinearities in the adiabatic vibronic energies produce large quantitative changes in the calculated cross sections, even for very weak coupling. Omission of a 0.4% reduction in frequency was found to overestimate the cross section by a factor of 10. (6) Calculations of transition rates between static states, although formally equivalent in perturbation expansion to those made for adiabatic states, differ greatly from the latter both because of the failure of perturbation theory and because the two sets of states describe very different physical systems.

Inelastic Electron Tunneling Spectroscopy in MIS and MS Tunnel Junctions

Calculation of the tunneling conductance for inelastic tunneling process with excitation energy \( \hbar \omega \) are carried out, and it is clarified that inelastic electron tunneling spectroscopy (IETS) can be a useful tool for investigation of electronic states in semiconductors. The electronic states of the semiconductor are related to the inelastic tunneling current in the bias range from \( \hbar \omega/e\) to \( \hbar \omega /e+V_{\text{F}}\). This bias increase of \( \hbar \omega/e\) brings some advantage such as separation of the electronic structure from zero bias anomaly and from other structure due to excitation in the barrier. In experiments for MS contacts of InSrTiO 3- x , concaves appeared in the d V /d J curves via inelastic tunneling process, and they were confirmed to be due to the electronic states of the SrTiO 3- x .

Electronic states of semiconductors with graded periodic inhomogeneities

Electronic states of semiconductors with graded periodic inhomogeneities

Surface Magnons and Analytic Continuation in the Cubic Systems

Magnetic excitations localized on the (001) surface of a cubic Heisenberg ferromagnet are considered theoretically by extending previous calculations by several authors, where only a simple cubic spin lattice was considered, to b. c. c. and f. c. c. spin lattices. The method can be easily generalized to any crystal symmetry, or any orientation of the axis of magnetization, assumed normal to the surface. This extension of the theory makes it possible to undertake in the future a comparison of theoretical calculations of the surface magnon despersionrelation, with, for instance, results of experiments with inelastic low energy electron diffraction on surfaces of, e. g. , some ferromagnetic rare-earth salts. The relationship has been shown between the surface spectrum and the analytic continuation to the complex k 3 plane of the bulk magnon dispersion relation, where a very close analogy can be found with the theory of surface electronic states in semiconductors.