Coupled electron–hole quantum well structure: mass asymmetry and finite widtheffects

Abstract

We investigate the role of many-body correlations in determining the ground-statebehaviour of the coupled electron–hole quantum well structure by including the massasymmetry and the finite width of wells. The correlations (both the intra- and inter-well)are treated beyond the static local-field theories by employing the dynamical self-consistentmean-field approximation of Hasegawa and Shimizu. The mass asymmetry is seen tointroduce a marked change in the ground state of the electron–hole system as compared tothe recent corresponding results on the mass-symmetric electron–hole bilayer.First, the critical density for the liquid–Wigner crystal phase transition is greatlyenhanced (e.g., by a factor of about 4 for a GaAs/GaAlAs based system). Second,there is a change in the role played by the electron–hole correlations. The Wignercrystal phase is now found to be stable below a critical density only at sufficientlylarge separation between the wells. The build-up of electron–hole correlationswith diminishing inter-well spacing tends to favour the charge-density-wave phaseover the Wigner crystal state, with the result that the former always prevails inthe sufficiently close approach of wells. This result differs strikingly from thecorresponding studies on the mass-symmetric system, since the electron–holecorrelations are predicted here to always support, at sufficiently small well spacing, theWigner crystal phase below a critical density and the charge-density-wave phaseat relatively higher densities. Further, we find that the inclusion of the finitewidth of layers results in lowering of the critical density for Wigner crystallization.