Complex Valence Band Research Articles

Weak localization in semiconductor structures with strong spin-orbit coupling

A theory of weak localization is constructed for p-type semiconductor structures with a complex Γ8 valence band. An equation for the Cooperon is obtained and solved in the case when spin relaxation cannot be treated as a perturbation. The anomalous magnetoresistance is calculated in bulk samples as a function of the external deformation and in quantum wells as a function of the doping level. The results of the theory are represented in a form that allows direct comparison with experiment.

Magneto-optical studies of excitons in Zn1-xCdxSe/ZnSe quantum wells.

Magnetoabsorption on high-quality ${\mathrm{Zn}}_{\mathit{x}}$${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$Se/ZnSe multiple quantum wells grown by molecular-beam epitaxy is used to study systematically the major excitonic properties. The small inhomogeneous width of the exciton lines allows us to observe Landau levels arising from higher heavy-hole exciton transitions as well as to analyze in detail the spin splitting and diamagnetic shift of the ground state. The Schr\"odinger equation of magnetoexcitons is solved numerically to describe their magnetic-field behavior and to deduce the relevant excitonic and band parameters in dependence on the Cd content in the well. Anticrossing features at higher Landau levels and the magnetic-field dependence of the light-hole exciton ground-state energy signify a complex valence-band structure due to heavy-light hole coupling. \textcopyright{} 1996 The American Physical Society.

Cyclotron resonance and subband-Landau level coupling in 2D electron and hole gases

We discuss the far-infrared absorption in quantum wells in the presence of a quantizing magnetic field. Our theory is applicable both to electrons and holes. Band structure effects are fully taken into account and our approach allows us to consider different sample geometries and potential profiles. As an example we discuss the spin-split cyclotron resonance in the non-parabolic 2D electron gas in InAs AlSb quantum wells. Our parameter-free calculations are in excellent agreement with recent experiments. The complex valence band structure results in anticrossings between Landau levels of different hole subbands.

Intersubband Transitions, Infrared Detectors, and Optical Nonlinearities in SiGe Multiquantum Wells

ABSTRACTA survey is given about the potential use of Si/SiGe heterostructures for applications in the mid-infrared spectral range. We discuss theoretical foundations and experiments of intersubband absorption in p-type Si/SiGe quantum wells and show that due to the complex valence-band structure, normal-incidence absorption can be observed. On the basis of these quantum wells, mid-infrared detectors were fabricated and characterized in terms of responsivity, dark current and detectivity. In asymmetric, compositionally stepped quantum wells second harmonic generation of CO2 laser radiation has been demonstrated.

Size-quantization of heavy holes with large momentum in complex valence band subjected to in-plane magnetic field

Heavy hole levels splitting in an infinitely deep rectangular potential well subjected to the external magnetic field parallel to the well side have been obtained in the limit of a large momentum along the surface.

Intrinsic dephasing times of photoexcited electron-valence-hole pairs near the Fermi edge of a degenerate electron gas in quantum wells.

Various single-particle and collective-mode scattering processes that contribute to the intrinsic dephasing time of photoexcited electron--valence-hole pairs in degenerate, modulation-doped quantum wells are discussed. Detailed calculations show that sharp discontinuities in the energy dependence of the electron dephasing time can give information about short-range correlations associated with large wave vectors and high-frequency excitations of the coupled electron--LO-phonon system. However, to extract dephasing times from coherent optical excitations the effects of the complex valence-band structure, i.e., mixing of light and heavy holes in GaAs quantum wells, must be considered.

Dephasing times in modulation-doped quantum wells

Various single-particle and collective-mode scattering processes that contribute to the dephasing time of photoexcited electron-valence hole pairs in degenerate, modulation-doped quantum wells are discussed. Detailed calculations show that sharp structures in the energy dependence of the electron dephasing time can give information about short-range correlations associated with large-wavevector and high-frequency excitations of the coupled electron-Lo phonon system. To extract dephasing times from coherent optical excitations the effects of the complex valence band structure, i.e. mixing of light and heavy holes in GaAs quantum wells, have to be taken into account. This is discussed in terms of the three-level semiconductor Bloch equations. Calculations are compared with recent experimental results by Kim et al.

Resonant inter-Landau-level tunneling of electrons and holes in superlattices

Inter-Landau-level tunneling of electrons and holes between two-dimensional (2D) systems is investigated in GaAs/AlAs superlattices. In one sample resonances due to electron tunneling up to Δ n = 9 ( n is the Landau level index) are observed. The corresponding Landau fan can be constructed when conduction-band nonparabolicities are included. In a second sample resonances due to inter-Landau-level tunneling of holes are identified. The experimental esults are discussed in view of the complex valence-band structure in the magnetic field.

Many-body effects in dense electron-hole plasma in InGaAs QWs with simple and complex valence band

High excitation magnetoluminescence spectra of highly homogeneous neutral electron-hole systems have been investigated in strained In x Ga 1− x As/GaAs and unstrained In 0.53Ga 0.47As/InP quantum wells (QW) with simple and complex valence band, respectively. A simple plasma model is found to describe satisfactorily the emission spectra from the dense EHP with large carrier temperature. The mass renormalization appears as a change of Landau level spacings. At n eh ≈ 10 12 cm −2, the interparticle interaction leads to ∼20% increase of the reduced mass micro −1 = m e −1 + m h −1 relative to its value in the empty ban renormalization strongly decreases with n eh. In the In 0.53Ga 0.47As/InP QW with small light-heavy hole subband splitting, Δ E v, there is an additional change in micro connected with the renormalization of Δ E v.

Photoemission studies of the interaction of Li and solid molecular oxygen.

The interaction of Li and oxygen has been studied at 25 K. This system serves as an excellent prototype for studying the interaction of alkali metals with oxygen. For some of the alkali metals, such as Cs or K, oxygen can be incorporated below the metal surface and complex valence-band and core-level features are obtained. In the case of Li at 25 K this does not appear to happen, and the core-level and valence-band features can be identified with the formation of the superoxide, the peroxide, and the oxide.

Surface electronic structure and chemisorption on corundum transition-metal oxides: alpha -Fe2O3.

Ultraviolet photoemission spectroscopy has been used to study the electronic structure of both nearly stoichiometric, well-ordered \ensuremath{\alpha}-${\mathrm{Fe}}_{2}$${\mathrm{O}}_{3}$ surfaces and surfaces containing point defects. The interaction of ${\mathrm{O}}_{2}$, ${\mathrm{H}}_{2}$O, ${\mathrm{H}}_{2}$, and ${\mathrm{SO}}_{2}$ with both types of surfaces has also been investigated. The energy levels of the five 3d electrons on the ${\mathrm{Fe}}^{3+}$ ions overlap those of the filled O 2p orbitals, leading to a complex valence band about 10 eV wide. Oxygen-vacancy surface defects produced by ${\mathrm{Ar}}^{+}$-ion bombardment result in a conducting surface layer containing both ${\mathrm{Fe}}^{2+}$ and ${\mathrm{Fe}}^{0}$ ions. The well-ordered \ensuremath{\alpha}-${\mathrm{Fe}}_{2}$${\mathrm{O}}_{3}$(0001) surface is relatively inert with respect to all four molecules studied, with exposures greater than ${10}^{3}$ L (1 L\ensuremath{\equiv}${10}^{\mathrm{\ensuremath{-}}6}$ Torr sec) necessary before any chemisorption could be seen. For large exposures, the ${\mathrm{O}}_{2}$-surface interaction gives rise to a negative adsorbed species. ${\mathrm{H}}_{2}$O adsorbs dissociatively on both well-ordered and defect surfaces, resulting in adsorbed ${\mathrm{OH}}^{\mathrm{\ensuremath{-}}}$ ions. ${\mathrm{SO}}_{2}$ appears to bond primarily to surface oxygen ions, yielding a complex similar to ${\mathrm{SO}}_{4}$${\mathrm{}}^{2\mathrm{\ensuremath{-}}}$.

Determination of Valence Band Parameters in ZnTe

AbstractThe fine structure of the 2P exciton in ZnTe is studied by two‐photon‐absorption. The energy splitting into four states, caused by the envelope–hole coupling, allows the determination of the Luttinger parameters γ2 and γ3, which describe the complex valence band. γ2, 0.8 and γ3 = 1.7 are obtained. These values will be compared to results of other experiments mainly on 1S excitons.

Excited states of bound excitons in wurtzite‐type semiconductors

AbstractExcitons bound to neutral impurities are studied with respect to excited states by means of excitation spectroscopy in CdS single crystals at 1.8 K. The symmetry of the four excited states of the exciton bound to neutral donor (placed energetically below the free exciton) can be deduced from the observed dependence of their optical transitions on the direction of the wave vector and the polarization. Theoretical considerations taking into account the complex valence band structure of wurtzite‐type semiconductors lead to an explanation of these states in terms of excited (p‐ and d‐like) hole states of the bound exciton. With respect to the exciton bound to neutral acceptor only the well‐known I1B‐states are found experimentally arising from the incorporation of a hole from the lower B‐subvalence band in the complex.

The free carrier magneto‐microwave effects in p‐type germanium

AbstractThe free carrier magneto‐microwave effects, namely, the Kerr effect, the Faraday rotation, and the magneto‐absorption, have been studied in detail in p‐type Ge in Faraday configuration. The experimental analysis applies to guided waves and treats multiple reflections exactly. The theoretical analysis takes account of the complex valence band structure and the contributions from the light and heavy holes, separately. The mixed scattering due to ionized impurities and lattice vibrations has been taken into consideration. The values of the ionized impurity scattering parameter and relaxation time obtained from Kerr effect measurements compare well with the values obtained by Faraday rotation measurements. Magneto‐absorption measurements have been done on the samples used for Faraday rotation measurements and the experimental results are compared with theoretical results using the transport parameters obtained from Faraday rotation measurements. Good agreement has been found between the two. The results of the above three types of measurements indicate the presence of larger impurity scattering and smaller relaxation time for light holes as compared with the heavy holes. The values of the relaxation times which has been estimated at 77 K (by Kerr effect measurements) compare well with the values obtained by earlier workers from cyclotron resonance and magneto‐plasma studies.

Inelastic effects and structure in the auger electron emission spectra of V2O5(010) and V(100) surfaces: Study of chemical shifts

Characteristic ionization losses and plasma losses occurring in the AES spectra of V 2 O 5 (010) and V(100) surfaces are discussed. The former are used to evaluate chemical shifts of the VL 2 and VL 3 levels in V 2 O 5 . Values of approximateley 2.5 eV are found. These are smaller than the values obtained with ESCA (± 5 eV). It is described how the electron beam used in AES is thought to be responsible for this effect. ESCA data from partly reduced V 2 O 5 samples tend to confirm the proposed model, based on oxygen loss and decomposition of V 2 O 5 single crystals under the influence of the electron beam. The plasma losses of the larger Auger peaks are discussed. It is shown how some fine structure in the spectra can be partly explained by their presence. The plasma losses were simulated with numerical techniques based on the use of a signal averager. Signal averaging, curve fitting and related numerical techniques improve the resolution of AES spectra. Spectra of V 2 O 5 (010) and V(100) obtained in this manner are discussed. With respect to the transitions involving the valence band it is shown that the complex valence band structure is one of the causes of the observed discrepancies between theoretical and experimental AES data. Furthermore there is an uncertainty concerning the way in which ionization correction should be applied in this case. This correction is thought to increase with the degree of localization of the valence electrons. Auger peak intensities in function of the primary energy were found to show a maximum at about 3.5 times the critical potential, as was expected from theory if a moderate amount of backscattering is taken into account. Finally the intensity variations of the Auger peaks under continuous electron bombardment show the rate of oxygen loss at a V 2 O 5 surface due to the primary beam.

Photoemission and Related Properties of the Alkali-Antimonides

The photoemissive process in the semiconducting alkali-antimonides is examined and values are given for the band gaps and electron affinities. The high photoelectric efficiencies of these materials are attributed to the ability of the excited electrons to traverse relatively large distances (250 A) without overwhelming energy losses, rather than to negligibly small electron affinities. The efficiency is found to be strongly dependent on the percentage of the electrons which are excited into states above the vacuum level. The properties of these materials depend to a large extent on the crystal structure. Cs3Sb and Na2KSb have a cubic structure, are p type, and seem to have a relatively simple valence band structure. K3Sb and Na3Sb have hexagonal crystal structures, are n type, and seem to have a relatively complex valence band structure. The evidence for an effect of band bending on the photoemission is considered.