Microscopic Studies of Schottky Barrier Nano-Contacts and Nano-Structured Metal/Semiconductor and Metal/Insulator Interfaces

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This project addresses fundamental materials science details of Schottky barrier nano contacts and nano-structured metal/semiconductor and metal/insulator interfaces The approach incorporates three sets of experiments to image, quantify, and model nm-scale electronic properties of metal-semiconductor (MS) and metal-insulator (MI) Schottky-barrier (SB) interfaces, which have nm-scale dimensions or nm-scale internal structure. Local SB properties will be measured with nm-resolution ballistic electron emission microscopy (BEEM), and 3D electrostatic modeling will be used to compare and correlate nm-scale SB properties with the total device electrical response. The first set of experiments will study SB nanocontacts where the semiconductor dimension is systematically varied down to ~ 1 nm, to probe how small-size effects (e.g. quantum-confinement and "environmental pinning") affect carrier injection into semiconductor nanostructures. A structure will be used consisting of a SB made on the cleaved face of a GaAs/AlGaAs heterostructure containing quantum wells (QWs) of different, precisely known width. These samples will also be used as nm-sized "apertures" for quantitative study of lateral hot-electron scattering and relaxation in metal films, including scattering processes within and between individual metal grains. A second set of experiments will use different sample structures for nm-resolution SB studies while a strong gate-field is applied to the SB contact. The main objective is to image and quantify how strong geometry-induced fields at defects and device edges affect the local SB properties and carrier injection through the SB. These sample structures will also be used for Ambipolar BEEM measurements, where the electron barrier and the hole barrier can be quantified at the same location, for example close to a particular defect. The third set of experiments will study metal-oxide-silicon (MOS) structures, where the metal film is a laterally nanostructured mixture of metals with very different workfunctions. The goal is to image, quantify, and model how lateral nm-scale structure in the metal film affects the local and average barrier height at the metal/oxide interface, and hence the resulting local and average electric fields in the oxide film and at the critical oxide/Si interface. A related goal is to investigate metal bilayers and other nanostructured metal films as possible "tunable workfunction" metals for future devices (MOSFETs). %%% The project addresses fundamental research issues associated with materials having technological relevance in nanoelectronics. An important feature of the project is the strong emphasis on education, with emphasis on integration of research and education. This project will provide a highly interdisciplinary and collaborative environment for graduate and undergraduate student training. Students are expected to develop a broad knowledge and training base by combining equipment construction, semiconductor processing, advanced experiments with novel equipment, numerical modeling, and frequent interactions with collaborators. Undergraduate and underrepresented students will continue to be actively recruited. Additionally, the PI will continue active involvement with science outreach, particularly in K-6 with science demonstrations, student interactions, and teacher mentoring.