Indirect electronic transitions in semiconductors occurring as a result of scattering of charge carriers by dislocations in a quantizing magnetic field

The light absorption due to indirect electronic transitions in a semiconductor in a quantizing magnetic field is calculated under the assumption that an edge dislocation plays the role of a third body. The characteristic light frequency and magnetic field dependences of the absorption coefficient are determined for the mechanism considered. Fiz. Tekh. Poluprovodn. 32, 453–454 (April 1998)     

Intraband light absorption in quasi-two-dimensional systems in external electric and magnetic fields

Intraband light absorption in parabolic quantum wells is studied with an electric field directed along the spatial quantization axis and a magnetic field parallel to the plane of the size-confined system. In such a geometry direct optical transitions between the quantum-well levels are possible, the peak light absorption coefficient reaches large values (∼3×10² cm⁻¹), and the frequency of the absorption maximum depends on magnetic field strength. It is shown for the normal incidence of electromagnetic waves that the level of absorption decreases with increasing electric field strength and that it is incorrect to confine the calculations to the Born approximation in strong magnetic fields. Fiz. Tekh. Poluprovodn. 33, 828–831 (July 1999)     

Modulation of optical absorption of GaAs/AlGaAs quantum wells in a transverse electric field

Results of experimental investigations of the transformation of intraband light absorption spectra by the quantum-well electrons in a transverse electric field are presented. In addition to the familiar Stark effect, absorption oscillations in the photoionization band are detected. These oscillations are caused by electron transitions from the ground state in a quantum well to quasidiscrete levels arising in the continuum of states above the well due to the linear potential of the external electric field. Fiz. Tekh. Poluprovodn. 32, 849–851 (July 1998)     

Light absorption and refraction due to intersubband transitions of hot electrons in coupled GaAs/AlGaAs quantum wells

Variation of the absorption coefficient and refractive index of a system of tunnel-coupled GaAs/AlGaAs quantum wells in a longitudinal electric field is discovered and investigated in the spectral region corresponding to intersubband electron transitions. The phenomena observed are explained by electron heating in the electric field and electron transfer in physical space. The equilibrium absorption spectra at lattice temperatures of 80 and 295 K are presented. Fiz. Tekh. Poluprovodn. 32, 852–856 (July 1998)     

Transport and optical properties of tin δ-doped GaAs structures

The transport and optical properties of tin δ layers in GaAs are investigated as functions of the Sn concentration. The Shubnikov-de Haas and Hall effects are measured in the temperature range 0.4–12 K in magnetic fields up to 38 T. The band diagrams and quantum mobilities of electrons in the quantum-well subbands are calculated. Features associated with electronic transitions from quantum-well levels are found in the photoluminescence spectra of the structures. Oscillations of the resistance are observed in a magnetic field parallel to the δ layer and are attributed to features in the density of states at the Fermi level. Fiz. Tekh. Poluprovodn. 33, 839–846 (July 1999)     

Spectrum and electron-phonon interaction in a medium with a cylindrical quantum wire

The effect of multiphonon processes on the electronic (hole) spectrum in a β-HgS/CdS nanoheterostructure (cylindrical quantum wire in a bulk medium) is studied in the dielectriccontinuum model. The electron-phonon interaction Hamiltonian is obtained for a potential well of finite depth. The shift of the electron (hole) energy level as a result of the interaction with optical longitudinal (confined) and interface phonons is determined. The dependence of the band gap of the nanosystem β-HgS/CdS on the radius of the quantum wire is found. It is established that interface phonons play the dominant role in the renormalization of the electronic (hole) spectrum in a quantum wire with small transverse dimensions. Fiz. Tekh. Poluprovodn. 33, 598–602 (May 1999)     

Photovoltaic effect in an asymmetric GaAs/AlGaAs nanostructure produced as a result of laser excitation

Photocurrent has been observed in a GaAs/GaAlAs structure with three asymmetric quantum wells in a magnetic field H parallel to the surface of sample irradiated with a quasicontinuous-wave laser with λ=1.065 μm. The current flows in the plane of the layers in a direction perpendicular to the magnetic field. The magnitude of the current increases with H, and when the magnetic field is switched, the sign of the photocurrent changes. The effect is explained on the basis of a model with asymmetric electronic wave functions in a magnetic field. Fiz. Tekh. Poluprovodn. 31, 872–874 (July 1997)     

Optical intersubband transitions in strained quantum wells utilizing In1−x GaxAs/InP solid solutions

Infrared absorption in strained p-type In_1−x Ga_xAs/InP quantum wells is investigated for both possible types of strain (tensile and compressive). It is observed that the normalincidence absorption increases considerably under compressive strain (when the ground state is a heavy-hole state) and decreases under tensile strain (when the ground state is a light-hole state). The peak absorption in the compressed quantum well can attain very large values, on the order of 5000 cm⁻¹ at a hole density ∼ 10¹² cm⁻²; this attribute makes “compressed” p-type quantum wells attractive for IR detection applications. Fiz. Tekh. Poluprovodn. 33, 83–90 (January 1999)     

Two electron transitions of the exciton bound at the Si Donor confined in GaAs/AlxGa1-xAs quantum wells

The exciton bound to the shallow Si-donor confined in a 100A wide GaAs quantum well has been studied in selective photoluminescence (SPL) and photoluminescence excitation (PLE) spectroscopy. The transition from the ground state, ls(Γ₆), to the first excited state, 2s(Γ₆), of the confined Si donor has been observed via two-electron transitions (TETs) of the donor bound exciton observed in SPL for the first time to the best of our knowledge. The interpretation of the TET peaks is confirmed by PLE measurements. Further, from Zeeman measurements, the magnetic field dependence of the donor ls(Γ₆)-2s(Γ₆) transition energy has been determined.     

Electron-phonon interaction and electron mobility in quantum-well type-II PbTe/PbS structures

Electron mobilities in PbTe layers were calculated, taking into account electron scattering by longitudinal polar optical phonons, for low-dimensional structures — multiple PbTe/PbS quantum wells, which are type-II structures. Comparison with the electron mobilities obtained from Hall coefficient and magnetoresistance investigations in undoped multiple PbTe/PbS quantum wells versus the magnetic field intensity showed good agreement between the computed and experimental results for these structures. Fiz. Tekh. Poluprovodn. 32, 739–742 (June 1998)     

Photoionization of deep impurity centers in quantum well structures

The absorption of light by photoionization of deep impurity centers in quantum well heterostructures is studied theoretically using a model with a maximally localized potential. Analytic expressions are found for the photoionization cross sections for light polarized perpendicular and parallel to the axis of the structure, disregarding the effect of the impurity potential on the continuum electronic states. The dependence of the frequency variation of the cross section on the charge state of the impurity after photoionization, as well as on the position of the impurity in the structure and the doping profile, is studied qualitatively near the absorption threshold. Fiz. Tekh. Poluprovodn. 33, 451–455 (April 1999)     

The effect of a “Coulomb well” on the absorption and magnetoabsorption spectra of strained InGaAs/GaAs heterostructures

The optical and magnetooptical properties of strained InGaAs/GaAs quantum-well heterostructures grown by molecular-beam epitaxy were studied at T=1.7 K in magnetic fields B⩽7.5 T. The well-resolved oscillatory structure of the magnetoabsorption spectra makes it possible to reproduce the “fan diagrams” for transitions between Landau levels of the HH1E1 quantum-confined states, taking into account exciton binding energies calculated variationally. Based on these results, reduced cyclotron masses of carriers were calculated for quantum wells with various indium contents. A self-consistent variational solution to the exciton problem in the structure under study shows that for weak type-II potentials the effect of Coulomb localization of the hole leads to a relative increase in the oscillator strength of the LH1E1 exciton transition. In this case the LH1E1 and LH3E1 exciton transitions remain spatially direct and retain a considerable intensity. The calculated splitting of ∼9 meV between these two states in zero magnetic field is found to be in agreement with experiment. The significant oscillator strength of light-hole excitons, along with the observed doublet structure, are experimental confirmations that electron-hole attraction can transform a rather low barrier for light holes in a type-II structure into a quantum well with a parabolic “Coulomb” shape near its bottom, i.e., a “Coulomb well.” Fiz. Tekh. Poluprovodn. 31, 1109–1120 (September 1997)     

Potential difference and photovoltaic effect arising from distortion of the electron wave function in a GaAs quantum well with a thin AlGaAs barrier

This paper discusses changes in the spectrum and distortion of the electron wave function of a GaAs quantum well when a thin AlGaAs barrier is introduced into it. The potential difference generated across the quantum well by distortion of the electron wave function is calculated, along with its dependence on the position of the barrier in the quantum well. The photovoltaic response of the structure to optical intersubband excitations is also calculated, along with the role of wave function and electronic spectrum distortion as well as intersubband nonradiative transitions in generating this response. The suitability of a GaAs quantum well with a thin barrier for use as an infrared detector is considered. Fiz. Tekh. Poluprovodn. 32, 1246–1250 (October 1998)     

Effect of anisotropy of band structure on optical gain in spherical quantum dots based on PbS and PbSe

Results of an experimental and theoretical study of the optical absorption spectra of spherical quantum dots based on PbS and PbSe are presented. A rigorous theoretical analysis of the energy spectra and optical transitions is performed within the framework of the four-band k·p approximation with full account of the effect of anisotropy of the band structure. It is shown that strong anisotropy of the band structure of PbS and PbSe leads to the appearance of optical transitions that are forbidden in the isotropic approximation. These transitions were detected in the optical absorption spectra of the investigated quantum dots. Fiz. Tekh. Poluprovodn. 33, 1450–1455 (December 1999)     

Energy spectrum and magnetooptical properties of a D (−) center in a quantum constriction

The states of the electron localized at a donor in the quantum constriction with parabolic electron potential in the presence of a magnetic field that is longitudinal with respect to the axis of the constriction are considered. The dispersion relation for electrons was derived analytically in the context of the model of the zero-radius potential taking into account the effect of a magnetic field on the D ^(?) state in the quantum constriction. It is found that the singularity in the electron spectrum in the quantum constriction manifests itself in the dependences of the binding energy of the D ^(?) state and the edge of the extrinsic-absorption band on the effective length of the constriction. The evolution of both the binding energy of the D ^(?) state and the spectrum of intrinsic magnetooptical absorption in the quantum constriction as the strength of a longitudinal magnetic is varied is studied. The results are compared with those in the case of the D ^(?) state in a quantum wire.     

Weak localization in p-type quantum wells

A weak-localization theory is derived for quantum heterostructures with strong spin-orbit interaction that predicts anomalous magnetoresistance. This theory treats real quantum wells with a few occupied quantum-well subbands. It is shown that in the presence of intense elastic transitions between these subbands the parameters that define the conductivity in classically weak magnetic fields are averaged efficiently. In the opposite limiting case, all the subbands give independent contributions to the anomalous magnetoresistance. Relevant characteristic magnetic fields are calculated for arbitrary ratios between the times for phase breaking and intersubband transitions. Fiz. Tekh. Poluprovodn. 32, 1219–1228 (October 1998)     

Magnetooptical properties of quantum wells with D (−) centers

The D ^(?) states in a quantum well under the magnetic field longitudinal with respect to the axis of growth of the structure are considered. In the context of the model of the zero-radius potential, an equation that defines the dependence of the binding energy of the D ^(?) state on the parameters of the potential of the structure, the coordinates of the D ^(?) center, and the strength of the magnetic field is derived. The results are compared with the experimental data on the dependence of the binding energy of the D ^(?) state on the magnetic field. There is satisfactory agreement between the theoretical calculations and experimental data in the range of magnetic fields B < 10 T. The role of dimensionality in the modification of the coordinate dependence of the binding energy on the 2D → 1D → 0D transition is clarified. The impurity magnetooptical absorption coefficient in a multiple quantum well structure is calculated, and the spectral dependence of the coefficient is studied. It is shown that a substantial contribution to the broadening of the absorption lines is made by the dispersion of quantum well widths in the structure.     

Shubnikov-de-Haas and de-Haas-van-Alphen oscillations in silicon nanostructures

The dependences of the longitudinal resistance and the static magnetic susceptibility on the magnetic field applied perpendicularly to the plane of an ultranarrow silicon quantum well confined by δ barriers heavily doped with boron demonstrate the high-temperature Shubnikov-de-Haas and de-Haas-van-Alphen oscillations in low magnetic fields. The results are indicative of the implementation of the high-field approximation μB ≫ 1 under these conditions due to the small effective mass of two-dimensional heavy holes, which is confirmed by measurements of temperature dependences of the de-Haas-van-Alphen oscillations.     

Interband magneto-absorption in narrow-gap HgTe/CdTe superlattice structures

The use of a magnetic field for interband absorption experiments in the midinfrared regime can reveal the electronic band structure of HgTe/CdTe superlattices. In high-quality samples pronounced magnetic field-induced absorption peaks are observed in the transmission spectra due to hole to electron Landau level transitions. By extrapolating the excitation energies for such transitions to B = 0, gap energies between several hole and electron subbands can be determined accurately. In addition, we show that interband magnetoabsorption provides a sensitive feedback for growth of quantum structures.     

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)