Sub-band populations and the spatial distribution of electrons in GaAs/(Al,Ga)As modulation-doped quantum wells

Abstract

High-field Hall and Shubnikov-de Haas (SDH) measurements on modulation-doped GaAs/(AI,Ga)As quantum well (awl structures have been interpreted on a model in which an asymmetric potential distribution across the QW causes a well-width-dependent spatial separation of the probability densities of electrons in different sub-bands. In narrow wells, <l50 A, this effect is small, and the electron distribution can be considered a s a single twodimensional electron gas (SDEG) extending throughout the well, with a low mobility characteristic of the inverted (GaAs on (AI,Ga)As) interface. In our wide well samples, 3 4 5 0 A, the electron density in the lowest sub-band is spatially concentrated near to the inverted interface, while the second sub-band has a peak density close to the normal, high mobility, interface; the electrons in these sub-bands t h u s have different mobilities, and magnetoresistance effects characteristic of parallel conduction in two distinct 2DEG channels are observed. For intermediate thickness wells, ~250-300 A, the two sub-band populations are close to those in the corresponding wide well samples, but because of the increased spatial overlap of the wavefunctions, the mobilities in the two subbands are similar. This results in a characteristic 'beating' phenomenon in the SDH curves. This model is shown to accord with published self-consistent calculations for modulation-doped quantum wells.

Magnetotransport in modulation-doped In0.53Ga0.47As/In0.52Al0.48As heterojunctions: in-plane effective mass, quantum and transport mobilities of 2D electrons

“…The in-plane effective mass of 2D electrons is similar to that of electrons in bulk In 0.53 Ga 0. 47 As and show no dependence on spacer thickness. The quantum mobility of 2D electrons is essentially independent of the thickness of the spacer layer in the range between 0 and 200 Å.…”

“…Our results for m * of 2D electrons in both the first and second subbands are in good agreement with the bulk effective mass in In 0.53 Ga 0. 47 As where m * was reported [36,37] to be in the range between 0.039m 0 and 0.041m 0 . This indicates that both the nonparabolicity of the conduction band of In 0.53 Ga 0.…”

“…This indicates that both the nonparabolicity of the conduction band of In 0.53 Ga 0. 47 As and the wavefunction penetration into the In 0.52 Al 0. 48 As barrier/spacer layer have no significant effects on m * of 2D electrons in our samples.…”

Landau-level interplay in InGaAs double quantum wells

“…The SdH oscillations in the longitudinal resistance (Fig. 1A) show a clear beating, which is evidence for the two electronic states with slightly different electron densities [1,3]. As a substrate bias is applied, the electron densities can be influenced and the beating is shifted.…”

“…Typically, such systems can be realized in wide quantum wells, where the two electron systems are separated electrostatically [1,2]. An alternative utilizes a double quantum-well (DQW) structure, where a large bandgap material separates the two systems [3][4][5][6].…”