M.A. Brummell

An experimental determination of enhanced electron g-factors in GaInAs-A1InAs heterojunctions

Abstract Electron g-factors have been determined in GaInAs-AlInAs heterojunctions using the tilted field method. The g-factor is found to be enhanced with values of |g∗| up to 15.5, compared with a bulk g ∗ = - 3 . |g∗| increases with increasing spin splitting providing evidence that the enhancement is due to many-body effects dependent upon a difference in spin populations. The deduced value of |g∗| is also found to be dependant upon the position of the Fermi level relative to the spin split Landau levels.

Quantum oscillations at a Ga0.47In0.53AsInP heterojunction interface

Abstract We report the observation of a two dimensional gas of high mobility electrons at the interface of a Ga 0.47 In 0.53 AsInP heterojunction grown by MOCVD. The two dimensional electron concentrations and effective mass are determined by Shubnikov-de Haas studies, and compared with theoretical predictions. Evidence of an enhancement of the g-factor is observed. We also report observations of very pronounced quantum Hall steps as seen in GaAs-GaAlAs heterojunctions.

Cyclotron resonance and polaron effects in a two-dimensional electron gas in GaInAs

Abstract Cyclotron resonance results from GaInAs-InP heterojunctions and superlattices and GaInAs-AlInAs heterojunctions in fields up to 18 T are reported. For low frequencies, the effective mass is compared with the predictions of k · p theory, and the resonance linewidth is fitted to finite range scattering theories. At higher frequencies, the linewidth increases dramatically, while the effective mass deviates from its low-frequency value. These effects are attributed to resonant polaron coupling.

Two-dimensional magnetophonon resonance in GaInAs-InP and GaInAs-AlInAs heterojunctions and superlattices

Abstract We report the observation of magnetophonon resonance in GaInAs-InP heterojunctions and measurements of the temperature dependence of the oscillations. A single series of oscillations due to scattering by the “GaAs-like” mode of GaInAs is seen, in contrast to GaInAs-InP superlattices, where scattering from InP phonons is also observed, and GaInAs-AlInAs heterojunctions, where coupling to “InAs-like” modes only is seen. This behaviour is discussed in terms of long-range phonon interactions and interface phonons.

High magnetic field studies of the two‐dimensional electron gas in GaInAs‐InP superlattices

We report the observation of Shubnikov–de Haas oscillations in superlattices of GaInAs and InP, showing evidence of two‐dimensional behavior. The electron g‐factor is deduced from both the criteria for resolution of a spin splitting by comparison with the broadening parameter Γ, and from the tilted field method, and is shown to increase with increasing resolution of the Landau levels in a manner consistent with the theory of Ando and Uemura. In the ultraquantum limit, structure at ν=1/2 and ν=1/3 is observed.

Millimeter and submillimeter detection using Ga1−xAlxAs/GaAs heterostructures

We have shown that a Ga1−xAlxAs/GaAs heterostructure can be used as a sensitive tunable detector of mm-wave/sub-mm-wave radiation. The mechanism for detection requires the application of a magnetic field varying from approximately 0.2T at 94GHz (3.2mm wavelength) to 6.2T at 2500GHz (119μm wavelength). The responsivity and N.E.P. at 3.2mm have been roughly estimated at 200V/W and 5×10−11W/✓Hz respectively. The speed of such a detector could be several orders of magnitude greater than comparable InSb detectors.

Competition between LO and TO phonon scattering in GaAs/GaAlAs heterojunctions

Abstract Magnetophonon resonance has been studied in GaAs/GaAlAs heterojunctions as a function of temperature, electron concentration and magnetic field orientation. The amplitude decreases rapidly with increasing carrier concentration, which is attributed to screening. The amplitude also decreases rapidly upon rotation relative to the magnetic field direction. The resonance positions give phonon frequencies closer to the bulk TO phonon than the bulk LO value when the field is perpendicular to the heterojunction interface, but move up towards the bulk value on rotation. This is thought to be due to anisotropic screening and its modification by subband mixing.

Frequency shifted polaron coupling in GaInAs heterostructures

Abstract Frequency dependent cyclotron resonance measurements are reported on Ga0.47In0.53AsInP and Ga0.47In0.53AsAl0.48In0.52As heterostructures. Discontinuities in the effective mass are observed at two frequencies, due to resonant polaron coupling to the two optic phonon modes in GaInAs. In heterojunctions the coupling occurs at the frequencies of the TO phonons, in contrast to bulk materials, and the relative strength of the coupling to the two modes is different in the two systems. In more lightly doped superlattices the coupling is stronger, leading to larger shifts in the effective mass, and occurs at the LO phonon frequencies. This behaviour is discussed in terms of possible changes in the screening and polarisation of the optic phonon modes.

Thermoelectric power of GaAs-GaAlAs heterostructures in high magnetic fields

Abstract We report measurements of the diagonal component of the thermoelectric power in a superlattice and a heterojunction of GaAs and GaAlAs. The qualitative variation of the thermopower with magnetic field is in agreement with both theoretical studies and previous experimental measurements. Quantitatively, the behaviour of the superlattice agrees with calculations for an ideal two-dimensional system, but both the magnitude and temperature dependence of the thermopower in the heterojunctions cannot be explained by existing theories.

Thermoelectric power of GaInAs-InP and GaInAs-AlInAs heterojunctions in a magnetic field

Abstract This work reports measurements of the diagonal thermopower in several heterojunctions based on Ga.47In.53As, in high magnetic fields and as a function of temperature. Structures have been studied in which only one or two electric subbands are populated, and in both cases the thermopower oscillations are in phase with the Shubnikov-de Haas oscillations in the resistivity, in accordance with theory. The absolute magnitude of the thermopower is found to be smaller than predicted by theory, and is also highly temperature dependent.