Current flow past an etched barrier: field emission from a two-dimensional electron gas

Abstract

PACS. 73.40Kp -III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions. PACS. 79.70.+q -Field emission, ionization, evaporation, and desorption.Abstract. -We find that, under appropriate conditions, electrons can pass a barrier etched across a two dimensional electron gas (2DEG) by field emission from the GaAs/AlGaAs heterojunction into a second, low-density 2DEG formed deep in the substrate. The current-voltage characteristics exhibit a rapid increase in the current at the field emission threshold and intrinsic bistability above this threshold, consistent with a heating instability occurring in the second 2DEG. These results may explain similar behaviour recently seen in a number of front-gated devices by several groups.Extensive studies of two-dimensional electron systems over the last two decades have relied on the ability to trap electrons at an interface between two materials with different band energies. Most popular amongst these systems is the high-mobility GaAs/Al x Ga 1−x As heterojunction [1]. Here the electrons are confined principally by attraction to remote donors placed in the AlGaAs. However, in order for there to be complete confinement there must also exist an electric field in the GaAs substrate pushing the electrons towards the heterojunction. In practice, this substrate field is typically provided by negative charge on residual acceptors in the substrate and surface boundary conditions [2]. A very interesting situation arises if this confinement field vanishes. The electrons are then predicted to be very weakly bound at the interface, by the work function of the 2DEG, as discussed by Groshev and Schoen [3]. The work function depends sensitively on the density of the 2DEG and is strongly influenced by many-body effects such as the image potential. Because of the weak confinement, field emission of electrons into the substrate may be anticipated in a weak electric field applied perpendicular to the interface.In this letter we discuss a simple device that demonstrates the field emission of electrons from a 2DEG. We find that a current can flow past an etched barrier in a 2DEG if the Typeset using EURO-T E X