Resonant coupling effects observed in independently contacted triple-quantum-well structures

Abstract

Independent contacts have been produced to all three two-dimensional electron gases (2DEGs) in a triple-quantum-well structure. This has been achieved by using in situ focused ion beam implantation followed by molecular beam epitaxial regrowth. Lateral transport studies of the individual layers have demonstrated resonant coupling between the high-mobility 2DEGs. Large resistance changes are observed due to coupling between the layers and these can be enhanced by having all three 2DEGs on resonance. A versatile device can thus be fabricated for studying electron interactions.

Exchange- and correlation-induced charge transfer observed in independently contacted triple-quantum-well structures

“…Details of the independent contacting to the three layers, and measurements of the coupling for this device are documented elsewhere. 7 Tunneling between the top and middle 2DEG's of the TQW structure was measured by forming independent contacts to the two 2DEG's. Figure 1 shows the tunnel conductance as a function of the front gate voltage, recorded for various back gate voltages.…”

“…This result is confirmed by magnetotransport measurements of each 2DEG separately, from which carrier densities can be accurately obtained. 7 The effect of altering the back gate voltage is to change the carrier density in the bottom 2DEG. If we assume that the bottom 2DEG acts as a perfect conductor, then it is able to screen the effect of the changing back gate potential from the upper 2DEG's, and the tunneling between the middle and top 2DEG's should be unaffected.…”

Probing the Fermi surfaces of coupled double quantum wells in the presence of an in-plane magnetic field

“…Using optical lithography, a Hall bar mesa (see figure 1(b)), was defined using wet etching and ohmic contacts formed using AuGeNi. Schottky NiCr-Au surface gates enabled both independent contacts [16] to be made to the uncoupled lower 2DEG and also allowed the density of the strongly coupled 2DEGs to be varied. The densities in the strongly coupled subbands at zero applied gate bias were 1.44×10 15 and 0.17×10 15 m −2 with mobilities 22 and 28 m 2 V −1 s −1 for the first and second subbands respectively.…”

“…In figure 3, the calculated dispersion curves and Fermi surfaces are shown for two gate voltages: (a) +0. 16 V and (b) −0.10 V. At B = 0 T the dispersion curves for the upper (dashed line) and lower (solid line) subbands are both centred upon k x = 0. The two curves, therefore, do not intersect and the number of populated subbands simply depends upon the position of the Fermi energy (E F ).…”