Negative differential resistance in AlAs/NiAl/AlAs metal base quantum wells: toward a resonant tunneling transistor

The authors report the observation of a negative differential resistance region (NDRR) in the axial current-voltage characteristics of a nominally 13-monolayer epitaxial NiAl film sandwiched between two 12-monolayer AlAs layers. The active area is separated by two 100-Å undoped GaAs regions from the heavily doped n-type GaAs electrodes on both sides. The NDRR is observable at room temperature in many of the devices but varies in strength across the wafer. The highest documented peak-to-valley ratio at room temperature is 2.0, but the majority of the devices exhibit lower ratios, typically around 1.2. The onset of the NDRR occurs around 800 meV. This value, however, contains the voltage drop at the top contact which is believed to be substantial. The origin of this effect is believed to be resonant tunneling through quantized electronic levels is the thin metal layer. This appears to be the first direct observation of size quantization in semiconductor-metal heterostructures