Interfacial electronic states in semiconductor heterostructures

It is shown that electronic states of a new type, with energy in the band gap can exist at a heterointerface. The interfacial states may be associated with Tamm surface states in the materials forming the heterointerface, but they can appear even if there are no surface states in the initial materials. In the plane of the heterojunction, the energy spectrum of interfacial states forms a two-dimensional band. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 6, 393–398 (25 March 1998)     

New envelope function for describing the electronic properties of semiconductor heterostructures

A new representation of the envelope function has been introduced, and is used as a framework for a proposed simple and at the same time precise formulation of a method for determining the electronic states in microstructures. The applicability of this method is demonstrated not only for structures with perturbations of the potential which are smooth on the scale of the crystal lattice but also for structures with sharp potential changes. Conditions are found for matching of the envelopes in the approximation of sharp heteroboundaries, which can be used in the “complex band structure” method. Matching conditions are found for the envelopes in the effective mass approximation and used to determine the limits of applicability of the well-known matching conditions of Ben Daniel and Duke. V. D. Kuznetsov Siberian Physicotechnical Institute at Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 22–31, August, 1996.     

Binding energy of a polaron in asymmetric polar semiconductor heterostructures

By using a modified Lee-Low-Pines variational method, we have investigated the ground-state binding energy of a polaron confined in asymmetric single and step quantum wells (QWs) due to interface phonons, confined bulk-like LO phonons, and half-space LO phonons. The relative importance of the different phonon modes is analysed in detail. Our results show that the asymmetry and the well width of the QWs have a significant influence on the polaron energy. The polaron binding energy has an intimate relation to the potential parameters of QWs. The subband nonparabolicity has a little influence to the polaron binding energy. Comparing with the results calculated with perturbation theory, a good agreement is found.     

Computer simulation study on the atomistic and electronic structures of semiconductor heterostructures

The atomic and electronic structures of semiconductor heterostructures are investigated by using the tight-binding (TB) electronic theory, taking into account the realistic atomic irregularities, such as steps and misfit dislocations at the interface. Particular attention has been paid to the 1/2〈110〉(001) misfit dislocation of the wide gap II-VI semiconductor heterostructures, like ZnSe/GaAs(001) systems. It is shown that steps at the interface do not produce deep gap states, but they influence significantly the deep states associated with the misfit dislocations. The stability and degradation of II-VI semiconductor heterostructures are discussed in terms of the introduction of the misfit dislocations.     

Optical phonon sidebands of electronic intersubband absorption in strongly polar semiconductor heterostructures

We present the first evidence for a distinct optical phonon progression in the linear and nonlinear intersubband absorption spectra of electrons in a GaN/Al(0.8)Ga(0.2)N heterostructure. Femtosecond two-color pump-probe experiments in the midinfrared reveal spectral holes on different vibronic transitions separated by the LO-phonon frequency. These features wash out with a decay time of 80 fs due to spectral diffusion. The remaining nonlinear transmission changes decay with a time constant of 380 fs. All results observed are described by the independent boson model.     

Polaron binding energy and effective mass in nitride single semiconductor heterostructures

Polaronic corrections in the conduction band of III–V nitride-based single heterostructures (SHS) are calculated within second-order Rayleigh–Schrödinger perturbation theory, using the dielectric continuum model for the interface and half-space polar optical phonon modes. The particular case of the AlN/GaN system is considered for illustration. The formation of a polarization-induced sheet density charge at the interface between both materials allows to study the single-electron states with the use of an approximate analytical expression for the potential energy function. The band-bending profile is then described in a way that includes many-body effects through a one-dimensional Hartree potential. Comparison of the calculated polaron effective mass in this material with recent experimental results in nitride SHS shows that higher perturbative orders in the interaction should be included in order to obtain better agreement.     

Quantum reflection pole method for determination of quasibound states in semiconductor heterostructures

The quantum reflection pole method (QRPM) is introduced for determining quasibound state eigenenergies and their lifetimes in symmetric, asymmetric, biased, and unbiased quantum heterostructures. In the QRPM the single-band effective-mass Schrödinger equation is solved without using complex arithmetic. Calculations are much simpler to perform than with previous methods. Further, results are found to be in excellent agreement with other rigorous techniques.     

Trap levels in layered semiconductor Ga2SeS

Trap levels in nominally undoped Ga₂SeS layered crystals have been characterized by thermally stimulated current (TSC) measurements. During the measurements, current was allowed to flow along the c-axis of the crystals in the temperature range of 10-300 K. Two distinct TSC peaks were observed in the spectra, deconvolution of which yielded three peaks. The results are analyzed by curve fitting, peak shape and initial rise methods. They all seem to be in good agreement with each other. The activation energies of three trapping centers in Ga₂SeS are found to be 72, 100 and 150 meV. The capture cross section of these traps are 6.7×10⁻²³, 1.8×10⁻²³ and 2.8×10⁻²² cm² with concentrations of 1.3×10¹², 5.4×10¹² and 4.2×10¹² cm⁻³, respectively.     

Chebyshev-series representation for the energy levels of U4+

Summary The energy levels of U⁴⁺ have been analysed using a ten-parameter Hamiltonian and, in particular, the effect of the magnetic and configuration interactions is examined. Bivariate polynomials of double Chebyshev series for each energy level are derived in terms of Marvin integralM ⁰ and configuration interaction parametera. A diagram showing transition fromLS tojj coupling is given. The author of this paper has agreed to not receive the proofs for correction.     

Low energy electronic states and triplet pairing in layered cobaltate

The structure of the low-energy electronic states in layered cobaltates is considered starting from the Mott insulating limit. We argue that the coherent part of the wave functions and the Fermi-surface topology at low doping are strongly influenced by spin-orbit coupling of the correlated electrons on the t(2g) level. An effective t-J model based on mixed spin-orbital states is radically different from that for the cuprates, and supports unconventional, pseudospin-triplet pairing.     

Validity of the transfer-matrix method for a two-dimensional electron waveguide

We solve the singularity problem of the transfer matrix method for a two-dimensional electron wave guide consisting of a sequence of cells. The method is reformulated in terms of intrinsic Bloch waves of a device cell. The resulting method is proved to be both stable and accurate. The transfer matrix is formulated without divergence problems in the open-mode approximation. The formula relating the N-cell transmission probability with that of one cell in the single-mode approximation takes exactly the same form as in the one-dimensional case.     

Electronic energy levels in semiconductor quantum wells and superlattices

We present the results of the calculations of some electronic properties of semiconductor quantum wells and superlattices. The review includes the superlattice band structure and the quantum well bound energy levels; the virtual bound states of semiconductor quantum wells and their influence on the energy spectrum of separate confinement heterostructures. Finally the perturbation of quantum well bound states and exciton states by a static electric field applied parallel to the growth axis is considered.     

A variational method for the calculation of spin-rovibronic energy levels of triatomic molecules with three interacting electronic states

A general method is presented for the evaluation of the spin rovibronic energy levels of triatomic molecules with up to three interacting potential energy surfaces. The full theory is outlined in detail, both for singlet and for doublet electronic states and the method is then applied to the benchmark example of C₂H. High quality multireference configuration interaction calculations have been carried out to generate the 3-dimensional near-equilibrium adiabatic potential energy surfaces of the three lowest 1²A'(X²Σ⁺), 2²A'(A²Π), 1²A''(A²Π) electronic states of C₂H, and the pair of interacting states of A 0 symmetry have then been diabatized. Results are presented for J up to 7/2 and compared with gas-phase high resolution experimental results for energies up to 5600 cm¹.