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.

A low temperature chemical vapor deposition (CVD) growth of Ge nanowires using Ga as seed material is demonstrated. The structural and chemical analysis reveals the homogeneous incorporation of ~3.5 at% Ga in the Ge NWs. The Ga-containing Ge nanowires behave like metallic conductors with resistivity values down to ~300 µΩcm due to Ga hyperdoping with electronic contributions of one third of the incorporated Ga atoms. This is the highest conduction values observed by in situ doping of group IV nanowires reported to date. This work demonstrates that Ga is both an efficient seed material at low temperatures for Ge nanowire growth and an effective dopant rendering the semiconductor into a metal-like conductor.

Recent advances in guiding and localizing light at the nanoscale exposed the enormous potential of ultra-scaled plasmonic devices. In this context, the decay of surface plasmons to hot carriers triggers a variety of applications in boosting the efficiency of energy-harvesting, photo-catalysis and photo-detection. However, a detailed understanding of plasmonic hot carrier generation and particularly the transfer at metal-semiconductor interfaces is still elusive. In this paper, we introduce a monolithic metal-semiconductor (Al-Ge) heterostructure device, providing a platform to examine surface plasmon decay and hot electron transfer at an atomically sharp Schottky nanojunction. The gated metal-semiconductor heterojunction device features electrostatic control of the Schottky barrier height at the Al-Ge interface, enabling hot electron filtering. The ability of momentum matching and to control the energy distribution of plasmon-driven hot electron injection is demonstrated by controlling the interband electron transfer in Ge leading to negative differential resistance.

Reconfigurable field‐effect transistors, capable of being dynamically programmed during run‐time, overcome the static nature of conventional complementary metal‐oxide semiconductors by reducing the transistor count and the circuit path delay. Thereby, SiGe and Ge are predicted to boost drive currents, switching speed and to reduce power consumption. Nevertheless, Ge‐based reconfigurable field‐effect transistor prototypes have so far fallen short in reaching both the promised performance due to interface instability to their contacts and gate oxides, as well as in reaching the current–voltage symmetry necessary for circuit applicability. Here, a top‐down fabricated SiGe‐based reconfigurable transistor technology is reported that is comprised of a vertical Si‐Si_0.67Ge_0.33 heterostructure enabling the envisioned high and symmetric on‐currents of both n‐ and p‐type operation. Monolithic integration with single‐elementary crystalline Al contacts alleviates process variability compared to conventional Ni‐silicide/Ni‐germanide contacts and introduces an ultra‐thin Si interlayer providing stability and equal injection efficiency of holes and electrons. The implementation of a three top‐gate transistor in combination with a hysteresis‐free Si/SiO₂/HfO₂ gate stack enhances polarity control and leakage current suppression to limit static power dissipation. Importantly, the obtained Al‐Si‐SiGe multi‐heterojunction and advanced reconfigurable transistor design is the first Ge‐based technology showing the envisioned stability and performance enhancements.