Surface acoustic wave attenuation by localized electrons in a 2DEG at a GaAs/AlGaAs heterojunction

Abstract

The surface acoustic wave (SAW) transmission has been measured at 4.2 K, as a function of magnetic field up to 5 T. for a GaAs wafer on which a heterojunction has been grown by MBE. Frequencies up to 1920 MHz were generated by interdigital SAW transducers deposited directly on the GaAs surface At all frequencies, oscillations in the SAW attenuation, analogous to the Shubnikov-de Haas oscillations in o x x , can be observed due to piezoelectric coupling to the non-localized electrons of the two-dimensional electron gas (ZDEG) of the heterojunction.We find, at frequencies of about 900 MHz and above, an additional attenuation at all magnetic fields, which increases with magnetic field. At half-integer filling factor, the increase in attenuation is initially linear with increase of field and then, at higher fields, the attenuation increases as the square root of the field. We interpret this as due to deformation potential coupling to the localized electrons of the 2DEG.A small SAW attenuation is observed at zero magnetic field which may be due to a very low density of three-dimensional electrons in the GaAs buffer layer or remaining in the doped AlGaAs layer.

Electron localization in sound absorption oscillations in the quantum Hall effect regime

“…However, this method is inconvenient because it is almost impossible to determine the width of the gap by direct measurements. In experiments employing the second configuration there is no gap at all, but in this case the deformation interaction of the 2D electrons with the SAWs cannot be ignored [6].…”

“…The first configuration was used in [4] and the second was used in [5][6][7][8]. In all of these investigations it was concluded that the character of the dependence of the SAW absorption coefficient of the two-dimensional electrons on the magnetic field H is determined by the dc conductivity σ dc xx (H) and its dependence on H. However, in [9], where the SAW absorption of a 2DEG in a InGaAs/InP heterostructure was measured in the first experimental configuration with T =4.2 K, it was shown that this assertion is valid only for high Landau-level numbers and in stronger magnetic fields (i.e., small filling numbers ν = nhc/2eH, where n is the Hall electron density) the variation of the SAW absorption coefficient as a function of H is not determined by σ dc xx (H).…”

Exciton ionization in a quantum well studied by surface acoustic waves

“…As has been pointed out before, SAW absorption measurements are particularly sensitive at very low conductivities, a fact that has been used before to study the dynamical conductivity of quasi-twodimensional electron systems ͑Q2DES͒ in the regime of the quantum Hall effect. [6][7][8] The design of our sample is shown in Fig. 1.…”

Voltage tunable acoustoelectric interaction in GaAs/AlGaAs heterojunctions

“…The interaction between surface acoustic waves ͑SAWs͒ and high-mobility quasi-two-dimensional electron systems ͑2DES͒ has recently attracted much attention. [1][2][3] SAWs proved to be a powerful tool for the investigation of the dynamical conductivity of such systems as they represent a highly sensitive dynamical probe which averages over the whole 2DES. SAW techniques have in the recent past been successfully applied to investigate the properties of a 2DES in the regimes of both the integer and the fractional quantum Hall effect at low temperatures and in high magnetic fields.…”