Dec 6, 2024
4:15pm - 4:30pm
Hynes, Level 2, Room 208
Alois Lugstein1,Zehao Song1,Masiar Sistani1,Fabian Schwingshandl1,Maximilian Bartmann1
Technische Universität Wien1
Alois Lugstein1,Zehao Song1,Masiar Sistani1,Fabian Schwingshandl1,Maximilian Bartmann1
Technische Universität Wien1
We will address the controlled formation of monolithic metal-semiconductor-metal nanowire and nanosheet heterostructures. The main obstacles facing towards reliable synthesis of such hybrid systems are related to lateral strain relaxation, mitigating the limitations of material lattice compatibility and allow arbitrarily combined dissimilar materials unattainable in layered structures. The formation of axial heterostructures with atomically sharp interfaces and monocrystalline aluminum by using a thermally initiated exchange reaction will be presented. Together with the wafer-scale accessibility, the proposed fabrication scheme may give rise to the development of key components for a broad spectrum of emerging Si and Ge-based devices requiring monolithic metal-semiconductor−metal heterostructures with high-quality interfaces for electrical, optical and plasmonic applications.<br/><br/>Aluminum is excellent for plasmonics because of a broad response spectrum from ultraviolet to infrared, a self-limited native oxide layer protecting the metal surface and CMOS-compatibility. Current Si-based ICs technology already uses nanoscale Al interconnects, to route electronic signals between transistors on a chip. With regard to scaling and integration, notably with the maturity of electromagnetic simulations and current CMOS fabrication techniques, a variety of such plasmonic designs can be fabricated in a Si foundry right now. Germanium as the channel material is advantaged by its full <i>compatibility</i> with CMOS technology to create a monolithic solution.<br/><b>The following particular features of the monolithic metal-semiconductor platform devices will be discussed:</b><br/>Light absorption, surface plasmon polariton (SPP) generation and guiding as well as effective injection of hot electrons/holes arising from the non-radiative decay of SPPs, is realized in a monolithic Al-Ge-Al Schottky barrier field effect transistor.<br/>The Al leads perform a dual function and simultaneously carry both optical and electrical signals, giving rise to exciting new capabilities.<br/>Via electrostatic modulation of the effective barrier height of the Schottky junctions, the transfer of hot charge carriers can be tuned with respect to their energy. For excited carriers arising from the non-radiative decay of SPPs the momentum must be in the direction to the metal-semiconductor junction, so that the carrier’s kinetic energy component in that direction is sufficient to overcome the effective Schottky barrier. The difficulty of achieving both energy and momentum matching is in general a main cause of the low quantum efficiency for extracting excited carriers in plasmonic devices. The actual monolithic device architecture is ideal in view of this as the SPPs are directly guided towards the Al-Ge interface.<br/>As a direct consequence of the monolithic architecture and thus improved momentum matching the devices have proven to be extremely effective plasmon detectors with an external quantum efficiency of EQE = 2.5%. Although no optimization with respect to effective plasmon coupling or SPP waveguiding has been done yet, this is quite remarkable since for other electrical plasmon detectors EQEs of less than 1% have been reported.<br/>Aside of barrier modulation a virtual p-n junction can be emulated in the semiconductor channel with top split-gates, with the distinct merit that carrier concentration and polarity are tunable by electrostatic gating. These investigations were carried out with a view to possible use for on-chip, CMOS-compatible plasmonic photovoltaics, with versatile implementations for autonomous nanosystems.<br/>Finally we will demonstrated the key functionality of a CMOS compatible transistor that response to plasmon signals in a neuron/synapse like fashion performing typical synaptic behavior, such as the excitatory post synaptic current and paired pulse facilitation.