Interband Transitions In Semiconductors Research Articles

Optical Orientation of Carriers in Interband Transitions in Semiconductors

Optical orientation, meaning the preferred orientation of the electron spin upon absorption of polarized light, is one of the most fruitful methods of spectroscopy and is extensively used for the investigation of atoms and ions [1]. Observation of optical orientation in a semiconducting crystal would make it possible to use the methods developed in atomic spectroscopy to investigate semiconductors and particularly to perform accurate measurements of the lifetime, the spin-relaxation time, the carrier g-factors, etc. So far, however, only one communication was published reporting such investigations in semiconducting crystals [2].

Photoexcitation of graphene with twisted light

We study theoretically the interaction of twisted light with graphene. The light-matter interaction matrix elements between the tight-binding states of electrons in graphene are determined near the Dirac points. We examine the dynamics of the photoexcitation process by posing the equations of motion of the density matrix and working up to second order in the field. The time evolution of the angular momentum of the photoexcited electrons and their associated photocurrents are examined in order to elucidate the mechanisms of angular momentum transfer. We find that the transfer of spin and orbital angular momentum from light to the electrons is more akin here to the case of intraband than of interband transitions in semiconductors, due to the fact that the two relevant energy bands of graphene originate from the same atomic orbitals.

Wave vector dependent magneto-optical interband transitions in semiconductors: Non-local effects

The well knows magneto-optical selection rule Δμ = 0, for one-photon interband transitions between Landau levels, is shown to be easily violated when the component of the optical wave vector perpendicular to the magnetic field is not negligible respect to the inverse of the magnetic length. The transition rate for the described optical absorption effect is discussed by adopting a gauge-independent description of the radiation-matter interaction Hamiltonian, such an approach is the correct one and leads to results different from the traditional approaches, in some cases of considerable amount.

Two-photon interband transitions in semiconductors in a static magnetic field. Nonlocal effects

It is shown that in the presence of a static magnetic field, the electronic states in the effective-mass approximation are described by a Hamiltonian containing a nonlocal potential. In order to preserve the gauge invariance of the transition rates, the interaction between the electrons and the radiation has to be modified. For ZnS, the transition rate between two particular levels is evaluated by showing a difference of more than one order of magnitude when compared with the transition rate previously calculated.

Saturation of interband transitions in semiconductors and the effect of optical bistability

Saturation of interband transitions in semiconductors and the effect of optical bistability

Joint density of states in interband transitions in semiconductors in a magnetic field

We consider impurity collision broadening of electron and hole Landau levels in a magnetic field, and the effect of electron-hole correlated impurity scattering to all orders on the joint density of states of interband transitions in a semiconductor. These renormalization mechanisms eliminate the divergences in the density of states associated with the unperturbed states for electrons and holes at Landau levels. This calculation has relevance in several physical situations involving interband transitions in the presence of a magnetic field; in particular, we discuss the calculation of gain for stimulated plasmon emission by electron-hole recombination in narrow-band-gap semiconductors.

Calculation of neutron cross sections for interband transitions in semiconductors

It has been proposed that the introduction of the high-flux high-energy pulsed-neutron sources will allow the study of electronic transitions between valence and conduction bands in semiconductors produced by inelastic scattering of neutrons. A theoretical calculation of the cross sections that would be expected in such an experiment is described. Results are presented for silicon and germanium. In calculating cross sections, which are based on an empirical pseudopotential description of the electronic band structure, it has been important to include both the spin and the orbital part of the magnetic scattering. It is found that, for the values of momentum transfer considered (up to about 10 ${\mathrm{nm}}^{\ensuremath{-}1}$), it is the orbital contribution that dominates. It is also shown that the matrix elements for the transitions have an important effect. Cross sections are shown for a range of energy and momentum transfer from which it is concluded that the experiment is likely to be possible, but questions of resolution will be of great importance if useful information about band structure is to be obtained.

ON THE THIRD ORDER OPTICAL NONLINEARITY OF SEMICONDUCTORS NEAR ITS ABSORPTION EDGE

A theory is proposed about the third order optical nonlinearity which is induced by the saturation effect of interband transitions in semiconductors near the absorption edge. The value of the exceptionally large nonlinear refractive index of InSb is given.

Polariton structure of interband transitions in semiconductors

AbstractA set of semiclassical wave equations is derived describing the interaction of virtual or real electron‐hole pairs with electromagnetic radiation. The solutions of these equations are the polaritons formed in an interband transition. They describe a renormalized photon surrounded by a cloud of electron hole pairs. The concept of interband polaritons is particularly useful for the understanding of effects that are sensitive to the structure of the electron‐hole cloud. As examples the phenomena of polariton free surface layers (similar to exciton free layers) and electronic Raman scattering in a depletion layer with distorted bands are discussed.

Self-induced transparency effect

A review is given of the current status of the self-induced transparency effect. The McCall–Hahn theory (2π pulses) is considered and its generalization to the case of phase modulation of radiation pulses, degeneracy of transitions, and two-photon resonance is discussed. The relationship with the theory of nonlinear waves, obeying the Korteweg–de Vries equation, is pointed out. The possibility of similar coherent effects in direct interband transitions in semiconductors is discussed. A summary is given of the experimental results demonstrating a strong fall in the absorption and a considerable slowing down of light pulses, typical of the self-induced transparency. Possible physical applications of the effect, based on these properties, are discussed.

Saturation of interband transitions in semiconductors

Summary form only, as given. Semiconductor behavior in strong fields having a frequency close to the absorption band is considered. It is proved that only the slowing down and recombination times of four different relaxation times are of importance for weaker fields. In this case, equality of Fermi-level electron and hole quasi-levels to light quantum energy corresponds to a saturation condition. A semiconductor absorption coefficient regarding saturation is calculated.