Sharka M. Prokes

Atomic Layer Deposition of Al2O3 on GaSb Using In Situ Hydrogen Plasma Exposure

In this report, we study the effectiveness of hydrogen plasma surface treatments for improving the electrical properties of GaSb/Al2O3 interfaces. Prior to atomic layer deposition of an Al2O3 dielectric, p-GaSb surfaces were exposed to hydrogen plasmas in situ, with varying plasma powers, exposure times, and substrate temperatures. Good electrical interfaces, as indicated by capacitance-voltage measurements, were obtained using higher plasma powers, longer exposure times, and increasing substrate temperatures up to 250 °C. X-ray photoelectron spectroscopy reveals that the most effective treatments result in decreased SbOx, decreased Sb, and increased GaOx content at the interface. This in situ hydrogen plasma surface preparation improves the semiconductor/insulator electrical interface without the use of wet chemical pretreatments and is a promising approach for enhancing the performance of Sb-based devices.

Carbon nanotube growth for field-emission cathodes from graphite paste using Ar-ion bombardment

Multiwall carbon nanotubes (MW-CNT) have been synthesized from solid-phase graphite. The graphite is deposited as a thick-film paste and irradiated with a 1.2keV flood Ar-ion beam, transforming the graphite surface to a composite of MW-CNT embedded in the graphite matrix. Micro-Raman measurements have verified that the nanotubes are metallic in nature. The technique was used to make printed field-emission cathodes. Emission from these cathodes demonstrates Fowler–Nordheim tunneling characteristics. The irradiated film emits at an extraction field of 5.0V∕μm, which is less than one-sixth of the minimum extraction field of the nonirradiated graphite film, and exhibit lower noise and greater emission uniformity.

Electronic properties of atomic-layer-deposited high-k dielectrics on GaSb(001) with hydrogen plasma pretreatment

In this report, the authors investigate the use of H2/Ar-plasma exposure as a means for achieving high-quality electrical interfaces between p-type GaSb and atomic-layer-deposited Al2O3 dielectric films. Dry in-situ plasma treatments are shown to reduce the estimated density of interface states by over two orders of magnitude compared to a standard wet HCl-treatment, without increasing gate leakage. The chemical compositions of the natively oxidized and treated GaSb surfaces are analyzed via x-ray photoemission spectroscopy (XPS). XPS spectra indicate that the native GaSb oxide is segregated, with Sb-oxide compounds localized at the air interface. Effective H2/Ar-plasma treatments act to remove the Sb-oxide, resulting in a surface Ga-oxide layer enriched in Ga2O3.

Clusters on semiconductor surfaces

Recent theoretical analysis and experimental investigations indicate that the physics of clusters deposited on semiconductor surfaces such as Silicon may be a promising future avenue for nanostructure science. Clusters of small number (5 - 10) of atoms in free space have also been shown to have interesting energy structures as well as magnetic and electrical moments. We report on the formation of Mn islands on Si(111) surfaces and their optical scattering response. We show that Mn islands of diameter 15 to 30nm exhibit paramagnetism at low temperatures, while thick films of Mn do not. In addition, our experiments verify previous theoretical suggestions that polarized optical scattering can be used to detect magnetism in small clusters. We will discuss some of these along with possible future applications of cluster physics.