Tunneling current bistability of correlated 2D electron–hole layers

Abstract

We study the low-temperature vertical tunneling current (TC) of a system of coupled 2D electron and hole gases (2DEG, 2DHG) of equal density realized in a single-barrier GaAs/AlAs/GaAs p–i–n heterostructure under conditions of forward bias. The density can be tuned by external voltage and the in-plane inter-particle distance can be made comparable to the layer separation (25 nm), the GaAs Bohr radius (12 nm), and the magnetic length for a perpendicular magnetic field B=10 T. We observe a discontinuous bistability in the I–V characteristic at T⩽300 mK, which has been never observed in n-type structures, and which is strongly enhanced for B=10 T. Out of the bistability, the current at fixed external voltage is observed to be exactly periodic in the inverse magnetic field for the high current states (HCS), while the 1/B oscillations of the low current states (LCS) are clearly phase shifted. The transition is found to be discontinuous both in the phase and in the period (i.e. density) in the region of bistability. We interpret the bistability as a phase transition between states of inter-layer correlated exciton-like states (LCS) and the two uncoupled free-carrier 2DEG and 2DHG (HCS) in our bilayer system.