Integration of Single -Walled Carbon Nanotubes With Gallium Arsenide(110) and Indium Arsenide(110) Surfaces: A Scanning Tunneling Microscopy Study

150 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007.In an effort to better elucidate the influence of semiconducting surfaces on supported carbon nanotubes, we have used scanning tunneling microscopy (STM) and spectroscopy (STS) to investigate the physical and electronic behavior of single-walled carbon nanotubes (SWNTs) coupled to GaAs(110) and InAs(110) substrates in ultrahigh vacuum (UHV). Both flat and stepped III-V(110) surfaces were obtained through in situ cleavage and nanotubes subsequently deposited onto the substrates via an UHV-compatible dry contact transfer procedure. STM images indicate that SWNTs on these III-V(110) surfaces possess a striking orientation-dependent adhesion preference, with nanotubes exhibiting an enhanced stability when aligned along the substrate lattice rows. STS measurements reveal the substrate-induced charge transfer doping of III-V-supported SWNTs and suggest the presence of potential orientation-dependent electronic effects in nanotubes on InAs substrates. The effects of proximal surface features, such as steps, on supported SWNTs are also explored. In addition, the simultaneous topographic and electronic imaging capabilities of the STM are exploited to obtain a detailed characterization of a naturally occurring metal-semiconductor intramolecular nanotube junction. Our studies indicate that local surface properties can have a considerable effect on the physical and electronic character of supported SWNTs, suggesting the exciting possibility of substrate-engineering for the design and fabrication of novel nanotube-based electronic devices.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD

Integration of Single -Walled Carbon Nanotubes With Gallium Arsenide(110) and Indium Arsenide(110) Surfaces: A Scanning Tunneling Microscopy Study

150 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007.In an effort to better elucidate the influence of semiconducting surfaces on supported carbon nanotubes, we have used scanning tunneling microscopy (STM) and spectroscopy (STS) to investigate the physical and electronic behavior of single-walled carbon nanotubes (SWNTs) coupled to GaAs(110) and InAs(110) substrates in ultrahigh vacuum (UHV). Both flat and stepped III-V(110) surfaces were obtained through in situ cleavage and nanotubes subsequently deposited onto the substrates via an UHV-compatible dry contact transfer procedure. STM images indicate that SWNTs on these III-V(110) surfaces possess a striking orientation-dependent adhesion preference, with nanotubes exhibiting an enhanced stability when aligned along the substrate lattice rows. STS measurements reveal the substrate-induced charge transfer doping of III-V-supported SWNTs and suggest the presence of potential orientation-dependent electronic effects in nanotubes on InAs substrates. The effects of proximal surface features, such as steps, on supported SWNTs are also explored. In addition, the simultaneous topographic and electronic imaging capabilities of the STM are exploited to obtain a detailed characterization of a naturally occurring metal-semiconductor intramolecular nanotube junction. Our studies indicate that local surface properties can have a considerable effect on the physical and electronic character of supported SWNTs, suggesting the exciting possibility of substrate-engineering for the design and fabrication of novel nanotube-based electronic devices.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD

Integration of atomic layer deposited high-k dielectrics on GaSb via hydrogen plasma exposure

In this letter we report the efficacy of a hydrogen plasma pretreatment for integrating atomic layer deposited (ALD) high-k dielectric stacks with device-quality p-type GaSb(001) epitaxial layers. Molecular beam eptiaxy-grown GaSb surfaces were subjected to a 30 minute H2/Ar plasma treatment and subsequently removed to air. High-k HfO2 and Al2O3/HfO2 bilayer insulating films were then deposited via ALD and samples were processed into standard metal-oxide-semiconductor (MOS) capacitors. The quality of the semiconductor/dielectric interface was probed by current-voltage and variable-frequency admittance measurements. Measurement results indicate that the H2-plamsa pretreatment leads to a low density of interface states nearly independent of the deposited dielectric material, suggesting that pre-deposition H2-plasma exposure, coupled with ALD of high-k dielectrics, may provide an effective means for achieving high-quality GaSb MOS structures for advanced Sb-based digital and analog electronics

Superior Growth, Yield, Repeatability, and Switching Performance in Gan-Based Resonant Tunneling Diodes

We report the direct measurement of record fast switching speeds in GaN/AlN resonant tunneling diodes (RTDs). The devices, grown by plasma-assisted molecular-beam epitaxy, displayed three repeatable negative differential resistance (NDR) regions below a bias of +6 V. A room temperature peak-to-valley current ratio (PVCR) \u3e 2 was observed, which represents a marked improvement over recent reports. Measurements carried out on hundreds of devices, of varying sizes, revealed a yield of ∼90%. Repeatability measurements consisting of 3000 sweeps resulted in a standard deviation, relative to the mean, of \u3c 0.1%. Temperature dependent measurements combined with non-equilibrium Green\u27s function based quantum transport simulations suggest the presence of both three-dimensional (3D) and two-dimensional (2D) emitters, giving rise to three NDR regions. Finally, a valley current density vs perimeter-to-area-ratio study indicates the presence of a surface leakage current mechanism, which reduces the PVCR

Effects of growth temperature on electrical properties of GaN/AlN based resonant tunneling diodes with peak current density up to 1.01 MA/cm2

Identical GaN/AlN resonant tunneling diode structures were grown on free-standing bulk GaN at substrate temperatures of 760 °C, 810 °C, 860 °C, and 900 °C via plasma-assisted molecular beam epitaxy. Each sample displayed negative differential resistance (NDR) at room temperature. The figures-of-merit quantified were peak-to-valley current ratio (PVCR), yield of the device with room-temperature NDR, and peak current density (Jp). The figures-of-merit demonstrate an inverse relationship between PVCR/yield and Jp over this growth temperature series. X-ray diffraction and transmission electron microscopy were used to determine the growth rates, and layer thicknesses were used to explain the varying figures-of-merit. Due to the high yield of devices grown at 760 °C and 810 °C, the PVCR, peak voltage (Vp), and Jp were plotted vs device area, which demonstrated high uniformity and application tunability. Peak current densities of up to 1.01 MA/cm2 were observed for the sample grown at 900 °C.publishedVersionPeer reviewe