Electronic Subband Energies Research Articles

Magnetotransport, magneto-optical and electronic subband studies in highly strained one-side-modulation-doped double quantum wells

Shubnikov - de Haas (SdH), Van der Pauw Hall effect and cyclotron resonance measurements on asymmetric double quantum wells grown by metalorganic chemical vapour deposition have been carried out to investigate the magnetotransport properties of an electron gas and to determine the effective mass of the electron gas, subband energies and wavefunctions in the quantum well. Transmission electron microscopy measurements show that a 50 Å InAs and a 100 Å quantum well were separated by a 30 Å potential barrier in an active region. The SdH measurements at 1.5 K demonstrated clearly the existence of a quasi-two-dimensional electron gas (2DEG) in the quantum wells. The fast Fourier transformation results for the SdH data indicate clearly the electron occupation of two subbands in the double quantum wells. The results of the cyclotron resonance measurements show that one absorption resonance is evidence of electron concentration occupied at the ground state subband in the double quantum well. The electron effective mass determined from the slope of the main peak absorption energies as a function of a magnetic field is . Electronic subband energies and energy wavefunctions in the quantum wells were calculated by a self-consistent method taking into account exchange correlation effects together with strain and non-parabolicity effects. The ground state subband wavefunction is strongly localized in the InAs quantum well side, and the first excited subband wavefunction in the asymmetric quantum well is very weakly coupled over both InAs and wells.

Structural, magnetotransport and electronic subband studies in a modulation-doped In0.65Ga0.35As/In0.52Al0.48As strained single quantum well

Shubnikov-de Haas (SdH) and Van der Pauw Hall effect measurements on a lattice-mismatched In0.65Ga0.35As/In0.52Al0.48As one-side-modulation-doped single quantum well grown by metalorganic chemical vapour deposition have been carried out to investigate the electrical properties of an electron gas and to determine the subband carrier densities, the subband energies and the wavefunctions in a strained In0.65Ga0.35As quantum well. Transmission electron microscopy measurements show that the In0.65Ga0.35As/In0.52Al0.48As heterointerfaces have no misfit dislocations. The SdH measurements at 1.5 K and fast Fourier transformation of the data show that a two-dimensional electron gas occupied three subbands in the well. The electronic subband energies and the wavefunctions in the quantum well have been calculated by a self-consistent method using the transfer matrix method based on the envelope-function approximation. The self-consistent calculation was performed taking into account exchange-correlation effects together with strain effects.

Terahertz acoustic-phonon signal generated by heated electrons in AlGaAs/GaAs-based quantum wires

In this paper, we explore theoretically the possibility of applying AlGaAs/GaAs-based quantum wire systems as a terahertz (THz) ultrasonic generator. For structures such as Al x Ga 1- x As/GaAs-based low-dimensional semiconductor systems and semiconductor nanostructures, electrons are confined within the nanometer distance scale so that energies (e.g. electronic subband energy, electron kinetic energy, Fermi energy, etc.) are in the meV scale, which consequently results in the acoustic-phonons generated by heated electrons from these novel systems to be around the THz frequency range. Our theoretical results indicate that: (i) Al x Ga - x As/GaAs-based quantum wires are suitable for generating THz acoustic-phonon signals; (ii) both longitudinal and transverse acoustic-phonon modes contribute to the detected phonon signals; (iii) the THz ultrasound wave can be generated through both intra- and inter-subband scattering processes; and (iv) the strong dependence of the acoustic-phonon emission from a quantum wire on phonon frequency and phonon emission angle can be observed.

Transition behavior from coupled to uncoupled CdTe/ZnTe asymmetric double quantum wells.

Photoluminescence (PL) measurements on CdTe/ZnTe double quantum wells grown by the simple method of double-well temperature-gradient vapor-transport deposition have been carried out to investigate the interband transitions in the double quantum wells. CdTe quantum wells were separated by a ZnTe potential-barrier width between 10 and 50 \AA{}. The results for the PL data at 15 K demonstrated clearly that the transition behavior from coupled to uncoupled peaks depends on the ZnTe barrier thickness. Electronic subband energies and wave functions in the quantum wells were calculated by an envelope-function approximation taking into account the strain effects, and the transition values were in good qualitative agreement with those obtained from the experimental measurements.

Interband transitions in CdTe/ZnTe single quantum wells grown by temperature-gradient vapor deposition

Several CdTe/ZnTe strained single quantum well structures with widths ranging from 5 to 20 Å were grown on GaAs (100) substrates by double-well temperature-gradient vapor-transport deposition. Photoluminescence (PL) measurements on the strained single quantum-well structures showed that the sharp excitonic peaks corresponding to the transitions from the first electronic subband to the first heavy-hole band (E1–HH1) below the critical thickness of the CdTe well were shifted to lower energy with increasing well width. However, the results of the PL spectra above the critical thickness of the CdTe clearly showed broad excitonic peaks, originating from the dislocations in the CdTe quantum well, corresponding to the (E1–HH1) transitions. Electronic subband energies were calculated by an envelope function approximation taking into account the strain effects, and the transition values were in good agreement with those obtained from the experimental measurements.

Electronic subband studies of InP/InAs/In xGa 1− xAs asymmetric double quantum wells

Shubnikov-de Haas (S-dH) and Van der Pauw Hall-effect measurements on InP/InAs/In x Ga 1− x As double quantum wells grown by metalorganic chemical vapor deposition have been carried out to demonstrate the existence of the two-dimensional electron gas (2DEG) in the double quantum wells. Transmission electron microscopy measurements showed that Inas and In 0.53Ga 0.47As quantum wells were separated by an In 0.25Ga 0.75As potential barrier in an active region. The results for the S-dH data and quantum Hall-effects at 1.5 K have demonstrated clearly the existence of a 2DEG in the quantum well. The fast Fourier transformation results for the S-dH data clearly indicate the occupation of two subbands in the coupled quantum wells. Electronic subband energies and wavefunctions in the quantum wells were calculated by a self-consistent method taking into account exchange-correlation effects. The first excited subband wavefunction in the asymmetric quantum well is weakly coupled over both InAs and In 0.53Ga 0.47As wells.

Electron occupation in subbands dependent on the indium mole fraction in [formula omitted] one-side-modulation-doped quantum wells

Shubnikov-de Haas (S-dH) and Van der Pauw Hall-effect measurements on In 0.53 Ga 0.47 As In 0.52 Al 0.48 As and In 0.65Ga 0.35 As In 052 Al 0.48 As one-side-modulation-doped quantum wells grown by metalorganic chemical vapor deposition have been carried out to investigate the magnetotransport properties of an electron gas and to determine the subband energies and wave functions in single quantum wells. Transmission electron microscopy measurements showed that the In 0.53 Ga 0.47 As In 0.52 Al 0.48 As heterointerfaces have a perfect lattice match and that the In 0.65 Ga 0.35 As In 0.52 Al 0.48 As heterointerfaces have a small lattice mismatch. The Shubnikov-de Haas measurements at 1.5 K demonstrated clearly the existence of a two-dimensional electron gas in the quantum wells. The fast Fourier transformation results for the S-dH data indicated clearly electron occupation of two and three subbands in the In 0.53Ga 0.47As and In 0.65Ga 0.35As single quantum wells, respectively. Electronic subband energies and wavefunctions in the quantum wells were calculated by a self-consistent method using the transfer matrix method based on the envelope-function approximation. These results indicate that the In x Ga 1− x As quantum well with the smaller energy gap has more electron occupation in the subband levels.

Electronic subband studies of a strained Al 0.22Ga 0.78As/In 0.15Ga 0.85As/GaAs one-side-modulation-doped quantum well

Shubnikov-de Haas and Van der Pauw Hall effect measurements on a strained Al 0.22Ga 0.78As/In 0.15Ga 0.85As/GaAs one-side-modulation-doped quantum well grown by molecular beam epitaxy have been carried out to investigate the properties of an electron gas in a single quantum well. Transmission electron microscopy measurements showed that the Al 0.22Ga 0.78As In 0.15Ga 0.85As and In 0.15Ga 0.85As GaAs interfaces have no misfit dislocations. The results of the Shubnikov-de Haas measurements and the observation of the quantum Hall effect at 1.5 K clearly demonstrated the existence of a two-dimensional electron gas in the quantum well, and the fast Fourier transform results for the S-dH data clearly indicate electron occupation of two subbands in the In 0.15Ga 0.85As single quantum well. Electronic subband energies and wavefunctions in the In 0.15Ga 0.85As quantum well were calculated by a self-consistent method taking into account exchange-correlation effects.

Electronic subband studies in In0.52Al0.48As/InxGa1−xAs one-side-modulation-doped asymmetric coupled double quantum wells

Shubnikov–de Haas (SdH) and van der Pauw Hall effect measurements on In0.52Al0.48As/InxGa1−xAs coupled double quantum wells grown by metalorganic chemical vapor deposition have been carried out to investigate the magnetotransport properties of an electron gas and to determine the subband energies and wave functions in the coupled quantum wells. Transmission electron microscopy measurements showed that In0.8Ga0.2As and In0.53Ga0.47As quantum wells were separated by an In0.25Ga0.75As potential barrier in an active region. The SdH measurements at 1.5 K demonstrated clearly the existence of a quasi-two-dimensional electron gas in the quantum wells. The fast Fourier transformation results for the SdH data clearly indicate the occupation of three subbands in the In0.52Al0.48As/InxGa1−xAs coupled quantum wells. Electron subband energies and wave functions in the quantum wells were calculated by a self-consistent method taking into account exchange-correlation effects. The first and second excited subband wave functions in the asymmetric quantum well are strongly coupled over both In0.8Ga0.2As and In0.53Ga0.47As wells.

Effect of cross-sectional geometry on the RPA plasmons of quantum wires

The effect of cross-sectional geometry on both the intrasubband plasmon and intersubband plasmon of a quantum wire is investigated within a two-subband RPA scheme. Exact analytical electronic wavefunctions for circular, elliptical and rectangular wires are employed within the infinite barrier approximation. It is found that for fixed cross-sectional area and linear electron concentration, the intrasubband plasmon energy is only marginally dependent on the wire geometry whereas the intersubband plasmon energy may change considerably due to its dependence on the electronic subband energy difference.

Temperature dependence of photoluminescence in InAsP/InP strained multiple quantum wells

The photoluminescence spectra of InAsP/InP strained multiple quantum wells have been experimentally determined in the temperature range 7–300 K. In order to understand the temperature behavior of the photoluminescence, a theoretical calculation is presented that takes into account the temperature-induced variations in band gap, carrier effective mass, biaxial strain, and exciton binding energy. The results show that the energy of the transition E1H between the n=1 electron subband and the n=1 heavy-hole subband changes as a function of temperature, and depends mainly on the evolution of the strained band gap of the InAsP layers. This is because in the temperature range 7–300 K the variations of the electron subband energy and the exciton binding energy are much less than those of the strained band gap, while the variation of the heavy-hole subband energy can be neglected. These results also explain why, for a lattice-matched quantum well, the variation of exciton peak energies with temperature follows that of the forbidden energy gap of the bulk material in the well.

Magnetotransport and electron subband studies of edge delta-doped Al0.27Ga0.73As/GaAs single quantum wells

Shubnikov–de Haas and Van der Pauw Hall effect measurements at 1.5 K have been carried out to investigate the existence of a two-dimensional electron gas and to determine subband energies in a Si-delta-doped Al0.27Ga0.73As/GaAs single quantum well. The fast Fourier transformation results for the S-dH data indicate clearly the occupation of two subbands in edge delta-doped Al0.27Ga0.73As/GaAs quantum wells. Capacitance-voltage profiling and temperature-dependent photoluminescence measurements have been performed to characterize the properties of edge delta-doped Al0.27Ga0.73As/GaAs quantum wells. Using these experimental results and a self-consistent numerical method which took into account the exchange-correlation effects, the electron subband energies were determined. These results indicate that edge delta-doped Al0.27Ga0.73As/GaAs single quantum wells are similar to the asymmetrical potential wells occupied by relatively high electron carrier densities.

Structural, magnetotransport and subband studies of an In0.52Al0.48As/In0.53Ga0.47As one-side modulation-doped quantum well

Shubnikov-de Haas (SdH) and van der Pauw Hall effect measurements on In0.52Al0.48As/In0.53Ga0.47As/In0.52Al$ d0.48As one-side modulation-doped quantum wells grown by metalorganic chemical vapour deposition have been carried out to investigate the magnetotransport properties of an electron gas and to determine the subband energies and wavefunctions in a single quantum well. Transmission electron microscopy measurements show that the In0.53 Ga0.47As/In0.52Al0.48As heterointerfaces have a perfect lattice match. The SdH measurements at 1.5 K have demonstrated clearly the existence of a quasi-two-dimensional electron gas in the quantum well. The fast Fourier transformation results for the SdH data indicate clearly the occupation of two subbands in the In0.53Ga0.47As single quantum well. Electron energy subbands in the quantum well were calculated by a self-consistent method taking into account exchange-correlation effects and making use of the experimentally determined carrier density.

Electronic envelope wave functions and subband energies in superlattice with a step-well basis

The envelope states in a superlattice with a step-well basis are studied. Analytical solutions of the electronic wave functions and subband energies for all values of the superlattice wave number are obtained explicitly. Numerical examples are also given. It is shown that the wave functions of the first subband are in general localized at the lowest well of a step-well basis, whereas the envelope states of the second subband basically extended to the whole step-well basis. This work can be regarded as an extension of the formalism of Pan and Feng [Phys. Rev. B44, 5668(1991)].

STUDY OF THE CHARACTERISTICS OF METALLIC ULTRA-FINE PARTICLES EMBEDDED IN HOST MEDIUM (I)——QUANTUM WELL DOT MODEL OF VLTRA-FINE PARTICLES

A quantum well dot model of ultra-fine particles (UFP) is presented in this paper. It is assumed that principal UFP characteristics are determined by non-localized electrons, which are restricted within a three-demensional potential well with finite depth (quantum well dot). Electronic characteristics are contributed by both of single-electron behavior and collective be-haviors. The electron energy spectrum is mainly determined by single-electron behavior. The model reflects the atomic properties, such as bulk work funtion, atomic radius and first ioni-zing energy value, and ignores the finer UFP structures. The approximation is proved rea-sonable. A number of useful formulae and predictions are derived. (1) The famous UFP cha-racteristics, quantum size effect and shell structures of electron energy spectrum, are derived from the quantum well dot model. (2) The UFP work function and Fermi-energy level, which is diffi-cult to be obtained by other models, are calculated. The formula that expresses the work func tion xarying with UFP size variation is derived, which explains well the experiments. The work function increases at first and then decreases gradually to bulk one with UFP size in-creasing. (3) The average energy space (AES) near Fermi- energy and the relationship bet-ween AES and electron interaction are derived. And the famous Kubo formula can be derived from quantum well dot model. (4) Finally, the model predicts the existence of electron energy subbands in UFP and semiconductor behavior of metallic UFP in some size. When particle size increases the sub-bands can not be discriminated and finally disappears, the particle shows complete bulk characteristics.

Electric subbands in a both-side-modulation-doped In0.52Al0.48As/In0.65Ga0.35As single quantum well

Shubnikov-de Haas and Van der Pauw Hall effect measurements on an In0.52Al0.48As/In0.65Ga0.35As lattice-mismatched single quantum well grown by molecular beam epitaxy have been carried out to investigate the electrical properties of an electron gas and subband energies in a unique potential well. The measurements at 1.5 K have demonstrated clearly the existence of a quasi-two-dimensional electron gas in the quantum well. It is found that three subbands in the quantum well are occupied. Electron energy subbands in the quantum well were calculated by a self-consistent method taking into account exchange-correlation effects and making use of the experimentally determined carrier density.

Electronic Wave Functions and Subband Energies in Superlattice with a Complex Basis

Electronic wave functions and energies in superlattice with a complex basis have been obtained that are more general than those of Pan et al. [Phys. Rev. B 44 (1991) 5668]. This paper gives not only subbands but also wave functions for all values of the wave number for superlattice with a complex basis.

Effect of spatial localisation of dopant atoms on the confining potential and electron subband structure in δ-doped GaAs:Si

In conjunction with Raman scattering measurements, we have performed calculations of the electronic structure of nominally δ-doped GaAs:Si in which tthe dopand layer has been positioned close (< 300 A ̊ ) to the surface, with a 200° Å spread towards the surface. The band-bending due to the Fermi level pinning at the surface gives rise to a strong asymmetric shape for the space charge induced potential well. Electron subband energies and wave functions are determined self-consistently and intersubband spin-density energies are compared with electronic Raman scattering results. A comparison of calculated and measured intersubband charge-density excitation energies is also made.

InAs quantum-well-base InAs/GaSb hot-electron transistors

Narrow InAs-base GaSb/InAs hot-electron transistors have been grown by low-pressure metalorganic chemical vapor deposition. The InAs bases are 30, 50, and 100 Å thick. The ground-state electron subband energy E0 is determined from values of collector current. For thinner wells, values of E0 are well explained by a simple effective mass calculation. Here, a mixing of InAs conduction-band states with GaSb valence-band states is neglected because of symmetry mismatch. The effect of nonparabolicity of the InAs conduction band is taken into account.

Quantization effect on capacitance-voltage and current-voltage characteristics of an InAs/AlSb/GaSb interband tunneling diode

Capacitance-voltage measurements were performed on the InAs/AlSb/GaSb interband tunneling diode at various frequencies. Theoretical analyses using a self-consistent Schrödinger–Poisson solver were found in agreement with the experimental results under the forward-bias condition. The quantization energy of each subband of the electron in the InAs accumulation region is used to predict the tunneling current cutoff voltage in agreement with that of the current-voltage measurements. Therefore, the cutoff of the interband tunneling process is mainly caused by the crossover of the electron subband energy in the InAs conduction band with respect to the valence band of the GaSb electrode due to the increased external bias voltage.