Negative transconductance in monocrystalline (Al,Ga)As/NiAl/(Al,Ga)As semiconductor/metal/semiconductor tunneling transistors

Abstract

The authors present the three-terminal transport characteristics of a resonant-tunneling semiconductor-metal-semiconductor (SMS) structure. The buried metal quantum well consists of a 3-nm-thick NiAl layer, epitaxially integrated in (Al,Ga)As, and is contacted by selectively removing the semiconductor overgrowth. The undoped AlAs tunneling barriers are 2 nm thick and are set back by 5 nm of undoped GaAs from the doped GaAs electrodes. The GaAs doping densities were adjusted to allow for the fabrication of emitter-up, collector-up, and symmetric transistors. The metal-semiconductor Schottky contacts between the NiAl and the cladding (Al,Ga)As layers were studied in order to characterize the individual interfaces and also to confirm the independence of the ultrathin buried metal electrode. Transistor action has been observed at room temperature in emitter-up structures with a wide (70 nm) undoped GaAs collector spacer. Room-temperature negative transconductance values as high as 1.4 mS/mm/sup 2/ have been obtained for large-area (80- mu m diameter) devices.