This work demonstrates with STM, STS, DFT, and device studies that TMA prepulsing on the As-rich InGaAs (2×4) surface reduces the trap state density by reducing As-As dimer bonds and As dangling bonds.

Formation of a contaminant free, flat, electrically passive interface to a gate oxide such as a-Al2O3 is the critical step in fabricating III-V metal oxide semiconductor field effect transistors; while the bulk oxide is amorphous, the interface may need to be ordered to prevent electrical defect formation. A two temperature in situ cleaning process is shown to produce a clean, flat group III or group V rich InGaAs surface. The dependence of initial surface reconstruction and dosing temperature of the seeding of aluminum with trimethylaluminum dosing is observed to produce an ordered unpinned passivation layer on InGaAs(001)-(4 × 2) surface at sample temperatures below 190 °C. Conversely, the InGaAs(001)-(2 × 4) surface is shown to generate an unpinned passivation layer with a seeding temperature up to 280 °C. For both reconstructions, the chemical drive force is consistent with formation of As-Al-As bonds. The optimal seed layer protects the surface from background contamination.

The megasonic cleaning efficiency is evaluated as a function of the angle of incidence of acoustic waves on a Si wafer. Acoustic Schlichting streaming alone is not able to remove nanoparticles smaller than 400 nm. It is shown that oscillating or collapsing behavior of bubbles are responsible for removing nanoparticles smaller than 400 nm during a cleaning process with ultrasound. Optimal particle removal efficiency is obtained around the angle of acoustic transmission of the silicon wafer.

High resolution STM images of In0.53Ga0.47As(001)-(2x4) were obtained and surface defects were quantified as a function of sample preparation technique. Published STM images of InGaAs(001)-(2x4) samples of varying In composition were examined and missing dimer unit cells, adatom trough defects, and incomplete atomic terraces were quantified for comparison with the In0.53Ga0.47As(001)-(2x4) surface. Density Functional Theory (DFT) modeling of α2(2x4) and β2(2x4) unit cell constructions and electronic structures show that the missing dimer defect creates conduction band edge states not readily passivated by trimethy aluminum; therefore, the density of dimer defects may cause trap state formation at oxide/InGaAs(001) interfaces.

The direct reaction of trimethylaluminum (TMA) on a Ge(100) surface and the effects of monolayer H(2)O pre-dosing were investigated using ultrahigh vacuum techniques, such as scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and x-ray photoelectron spectroscopy (XPS), and density functional theory (DFT). At room temperature (RT), a saturation TMA dose produced 0.8 monolayers (ML) of semi-ordered species on a Ge(100) surface due to the dissociative chemisorption of TMA. STS confirmed the chemisorption of TMA passivated the bandgap states due to dangling bonds. By annealing the TMA-dosed Ge surface, the STM observed coverage of TMA sites decreased to 0.4 ML at 250 °C, and to 0.15 ML at 450 °C. XPS analysis showed that only carbon content was reduced during annealing, while the Al coverage was maintained at 0.15 ML, consistent with the desorption of methyl (-CH(3)) groups from the TMA adsorbates. Conversely, saturation TMA dosing at RT on the monolayer H(2)O pre-dosed Ge(100) surface followed by annealing at 200 °C formed a layer of Ge-O-Al bonds with an Al coverage a factor of two greater than the TMA only dosed Ge(100), consistent with Ge-OH activation of TMA chemisorption and Ge-H blocking of CH(3) chemisorption. The DFT shows that the reaction of TMA has lower activation energy and is more exothermic on Ge-OH than Ge-H sites. It is proposed that the H(2)O pre-dosing enhances the concentration of adsorbed Al and forms thermally stable Ge-O-Al bonds along the Ge dimer row which could serve as a nearly ideal atomic layer deposition nucleation layer on Ge(100) surface.

The electronic passivation of a Ge(100) surface, via the chemisorption of H2O at room temperature (RT), and the temperature dependence of H2O coverage were investigated using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). With a saturation H2O dose at RT, a highly-ordered structure, due to the dissociative chemisorption of H2O, was observed on a Ge(100) surface with a coverage of 0.85 monolayers (ML). Annealing the room temperature H2O-dosed Ge surface to 175°C decreased the coverage of H2O to 0.6ML. Further annealing at 250°C decreased the coverage of H2O sites to 0.15ML, and the surface reconstruction of Ge dimers was observed over much of the surface. Annealing above 300°C induced Ge suboxide structures, similar to the oxygen-dosed Ge surface. STS measurements confirmed that the surface dangling bond states near Fermi energy are removed by the H2O chemisorption because the dangling bonds of Ge atoms are terminated by ―OH and ―H. The H2O pre-dose at room temperature provides a template for the ultrathin passivation of Ge(100) surface via atomic layer deposition (ALD) at RT, since near monolayer nucleation can be obtained with a 1/2 hydroxylated and 1/2 hydrogenated Ge surface.

Air exposed III-V surfaces nearly always have electronic defects which prevent full modulation of the Fermi level thereby impeding their use in practical semiconductor devices such as metal oxide field effect transistors (MOSFETs). For a high speed device, the air induced defects and contaminants need to be removed to reduce trap states while maintaining an atomically flat surface to minimize interface scattering thereby maintaining a high carrier mobility. Using in-situ atomic scaling imaging with scanning tunneling microscopy, a combination of atomic hydrogen dosing, annealing and trimethyl aluminum dosing is observed to produce an ordered passivation layer on air exposed InGaAs(001)-(4×2) surface with only monatomic steps.

Ga2O and In2O oxides were deposited on In0.53Ga0.47As(0 0 1) (4 2) surface by a high temperature effusion cell to investigate the interfacial bonding geometries and electronic structures by scanning tunneling microscopy/spectroscopy (STM/STS). At low coverage, Ga2O molecules bond to the As atoms at the edge of the rows and preexisting Ga2O on the surface. Annealing the Ga2O/In0.53Ga0.47As(0 0 1) (4 2) to 340 C results in formation of slightly ordered islands running in the [ 1 1 0] direction and rectangle shape flat islands on the surface. At high coverage with 340 C post-deposition annealing (PDA), Ga2O oxides form disordered structures with the large flat terraces on the surface. Conversely, at high coverage with 380 C PDA, In2O on In0.53Ga0.47As(0 0 1) (4 2) forms ordered structures running in the [1 1 0] direction. STS results show that Ga2O oxide does not passivate the interface nor unpin the In0.53Ga0.47As(0 0 1) (4 2) surface consistent with its inability to form monolayer ordered islands on the surface; conversely, In2O/In0.53Ga0.47As(0 0 1) (4 2) has an ordered monolayer coverage and is unpinned. 2010 Elsevier B.V. All rights reserved.

Using in situ atomic scale imaging with scanning tunneling microscopy/spectroscopy, a combination of atomic hydrogen dosing, annealing, and trimethyl aluminum dosing is observed to produce an ordered unpinned passivation layer on an air exposed InGaAs(001)-(4 × 2) surface with only monatomic steps. This shows that conventional gate-last semiconductor processing can be employed to fabricate a variety of electronic devices, even on air exposed compound semiconductors.

Oxide monolayers and submonolayers formed by vapor depositon of In2O and SiO oxides on InAs(001)-(4x2) were studied by scanning tunneling microscopy (STM). At low coverage, In2O molecules bond to the edges of the rows and most likely form new In-As bonds to the surface without any disruption of the clean surface structure. Annealing the In2O/InAs(001)-(4x2) surface to 380 C results in formation of flat ordered monolayer rectangular islands. The annealed In2O no longer bonds with just the As atoms at the edge of row but also forms new O-In bonds in the trough. SiO chemisorption on InAs(001)-(4x2) is completely different than In2O chemisorption. At room temperature, even at low coverage SiO adsorbates bond to themselves and form nanoclusters. For SiO/InA(001)-(4x2) post-deposition annealing (PDA) does not disperse the nanoclusters into flat islands. Both In2O and SiO depositions on InAs(001)-(4x2) surface do not displace surface atoms during both room temperature deposition and post-deposition annealing.

Kelvin probe force microscopy (KPFM) is a unique technique that can provide two-dimensional potential profiles inside a working device. A procedure is described to obtain high-resolution KPFM results on ultra-high vacuum (UHV) cleaved III-V MOSCAPs. Two tip preparation methods: field emission and Cr coating show reproducible high spatial and energy resolution KPFM images. A unique sample design has been developed which is compatible with UHV cross-sectional KPFM (x-KPFM). Key design features are high density of devices on the cleave face, a buried device interface, and a cleavable gate contact. Using x-KPFM, the first UHV cleaved MOSCAP surface potential mapping is demonstrated.

Oxide monolayers and submonolayers formed by vapor depositon of In2O and SiO oxides on InAs(001)-(4x2) were studied by scanning tunneling microscopy (STM). At low coverage, In2O molecules bond to the edges of the rows and most likely form new In-As bonds to the surface without any disruption of the clean surface structure. Annealing the In2O/InAs(001)-(4x2) surface to 380åC results in formation of flat ordered monolayer rectangular islands. The annealed In2O no longer bonds with just the As atoms at the edge of row but also forms new O-In bonds in the trough. SiO chemisorption on InAs(001)-(4x2) is completely different than In2O chemisorption. At room temperature, even at low coverage SiO adsorbates bond to themselves and form nanoclusters. For SiO/InA(001)-(4x2) post-deposition annealing (PDA) does not disperse the nanoclusters into flat islands. Both In2O and SiO depositions on InAs(001)-(4x2) surface do not displace surface atoms during both room temperature deposition and PDA.

Kelvin probe force microscopy (KPFM) is a tool that enables nanometer-scale imaging of the surface potential on a broad range of materials. KPFM measurements require an understanding of both the details of the instruments and the physics of the measurements to obtain optimal results. The first part of this review will introduce the principles of KPFM and compare KPFM to other surface work function and potential measurement tools, including the Kelvin probe (KP), photoemission spectroscopy (PES), and scanning electron microscopy (SEM) with an electron beam induced current (EBIC) measurement system. The concept of local contact potential difference (LCPD), important for understanding atomic resolution KPFM, is discussed. The second part of this review explores three applications of KPFM: metallic nanostructures, semiconductor materials, and electrical devices.

Ga"2O and In"2O oxides were deposited on In"0"."5"3Ga"0"."4"7As(001)-(4x2) surface by a high temperature effusion cell to investigate the interfacial bonding geometries and electronic structures by scanning tunneling microscopy/spectroscopy (STM/STS). At low coverage, Ga"2O molecules bond to the As atoms at the edge of the rows and preexisting Ga"2O on the surface. Annealing the Ga"2O/In"0"."5"3Ga"0"."4"7As(001)-(4x2) to 340^oC results in formation of slightly ordered islands running in the [[email protected]?10] direction and rectangle shape flat islands on the surface. At high coverage with 340^oC post-deposition annealing (PDA), Ga"2O oxides form disordered structures with the large flat terraces on the surface. Conversely, at high coverage with 380^oC PDA, In"2O on In"0"."5"3Ga"0"."4"7As(001)-(4x2) forms ordered structures running in the [110] direction. STS results show that Ga"2O oxide does not passivate the interface nor unpin the In"0"."5"3Ga"0"."4"7As(001)-(4x2) surface consistent with its inability to form monolayer ordered islands on the surface; conversely, In"2O/In"0"."5"3Ga"0"."4"7As(001)-(4x2) has an ordered monolayer coverage and is unpinned.