Abstract
Conductance quantization at room temperature is a key requirement for the utilizing of ballistic transport for, e.g., high-performance, low-power dissipating transistors operating at the upper limit of “on”-state conductance or multivalued logic gates. So far, studying conductance quantization has been restricted to high-mobility materials at ultralow temperatures and requires sophisticated nanostructure formation techniques and precise lithography for contact formation. Utilizing a thermally induced exchange reaction between single-crystalline Ge nanowires and Al pads, we achieved monolithic Al–Ge–Al NW heterostructures with ultrasmall Ge segments contacted by self-aligned quasi one-dimensional crystalline Al leads. By integration in electrostatically modulated back-gated field-effect transistors, we demonstrate the first experimental observation of room temperature quantum ballistic transport in Ge, favorable for integration in complementary metal–oxide–semiconductor platform technology.
Highlights
A fter decades, following Moore’s law[1] by continuously shrinking feature sizes of classical planar metal-oxidesemiconductor field-effect transistors (FETs), physical limitations and the dramatic repercussions of short-channel effects[2] have forced a shift of research efforts toward the integration of new materials, novel processing techniques, and ultrascaled device architectures.[3]
Conductance quantization at room temperature is a key requirement for the utilizing of ballistic transport for, e.g., highperformance, low-power dissipating transistors operating at the upper limit of “on”-state conductance or multivalued logic gates
Utilizing a thermally induced exchange reaction between single-crystalline Ge nanowires and Al pads, we achieved monolithic Al−Ge−Al NW heterostructures with ultrasmall Ge segments contacted by self-aligned quasi onedimensional crystalline Al leads
Summary
Heterostructure formation process via a thermally controlled exchange reaction between the single-crystalline Ge NWs and Al contact pads.[28]. This is supported by the enlarged view in the inset of Figure 2b, which shows that the resistance of Al−Ge−Al NW heterostructures with ultrascaled Ge channels is approaching the fundamental contact resistance of RC = 12.9 kΩ, which is a first indication of ballistic transport.[39] For thin Ge NWs with diameters of about 25 nm and, close to aGe, quantum confinement results in a band structure being composed of multiple 1D sub-bands. By utilizing a controlled thermal exchange reaction between single-crystalline VLS-grown Ge NWs and Al pads, we demonstrated room-temperature quantum ballistic transport in back-gated Al−Ge−Al NW heterostructure devices with ultrascaled Ge segments.
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