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Notes: By combining a low temperature (600 °C) chemical vapor deposition process for homoepitaxial diamond and conventional ion implantation, we have made and lifted off a synthetic diamond single crystal plate. Before growth, a type Ia C(100) crystal was exposed to a self implant of 190 keV energy and dose of 1×1016 cm−2. Homoepitaxial diamond growth conditions were used that are based on water-alcohol source chemistries. To achieve layer separation ("lift-off''), samples were annealed to a temperature sufficient to graphitize the buried implant-damaged region. Contactless electrochemical etching was found to remove the graphite, and a transparent synthetic (100) single crystal diamond plate of 17.5 μm thickness was lifted off. This free-standing diamond single crystal plate was characterized and found to be comparable to homoepitaxial films grown on unimplanted single crystal diamond. © 1996 American Institute of Physics.

Notes: In situ cleaning of GaAs surfaces has been achieved at 350 °C with a novel technique employing hydrogen that is excited and dissociated using a remote Ar discharge. Reconstructed surfaces characteristic of clean, As-stabilized GaAs surfaces have been observed with reflection high-energy electron diffraction following the cleaning treatment. Auger electron spectroscopy analyses confirm that such a treatment removes both carbon and oxygen contamination from the surface. X-ray photoelectron spectroscopy shows the removal of oxygen bonded to both Ga and As on the surface. Emission spectroscopy shows evidence of excited molecular and atomic hydrogen with the downstream-excitation process.

Notes: Recent studies [Hattangady et al., Appl. Phys. Lett. 57, 581 (1990)] have shown greatly reduced interface state densities (5×1010 cm−2 eV−1) in Ge-based, metal-insulator-semiconductor structures with the use of an ultrathin, pseudomorphic Si interlayer between the gate dielectric, SiO2, and the Ge semiconductor substrate. The Si and the SiO2 layers are deposited in situ and sequentially at low temperature (300 °C) in a remote-plasma-enhanced chemical-vapor-deposition system. This report presents an analysis of the Si-Ge heterostructure before and after the SiO2 deposition. Low-energy He ion scattering spectroscopy shows that the silicon layer (28 A(ring)) provides complete coverage of the Ge surface prior to the deposition of the SiO2 film. The existence of the silicon interlayer after the remote-plasma-enhanced deposition of 150 A(ring) of the SiO2 film is established by x-ray photoelectron spectroscopy (XPS). Throughout a cumulative series of thin (∼10 A(ring)) oxide depositions, XPS showed no evidence of Ge oxidation states other than Ge0+ (elemental Ge) at the interface. Quantitative XPS has been used to evaluate the extent of subcutaneous oxidation which could determine the amount of Si remaining at the interface and thereby influence the electrical properties of the semiconductor-oxide interface. For the conditions studied, it is observed that oxidation consumes only 4 A(ring) of the initial 28 A(ring) of silicon.Furthermore, this is apparently due to the plasma oxidation of the silicon at the initiation of the remote oxygen plasma discharge. Subcutaneous oxidation is limited thereafter by the oxide film that forms a barrier to oxygen diffusion. In addition, the XPS analysis reveals several important characteristics of SiO2-Si interface formation with these plasma-deposited SiO2 dielectric films. Inversion-mode, p-channel Ge field-effect transistors fabricated with this composite SiO2-Si gate dielectric structure show a maximum room-temperature transconductance of 52 mS mm−1 at a gate length of 2 μm and a peak effective channel hole mobility of 430 cm2 V−1 s−1. These devices exhibit negligible charge-induced threshold shifts.

Notes: Epitaxial Ge films have been deposited at 300 °C using a remote plasma-enhanced chemical-vapor deposition technique where metastable He atoms flow downstream from the plasma region to dissociate GeH4 molecules into deposition precursor species. Ge epitaxy is demonstrated on Ge(111), Si(100), and GaAs(111)Ga face substrates. An in situ cleaning process that involves a moderate thermal bake at 300 °C and a hydrogen plasma etch of the native oxides is integral to the process. Reflection high-energy electron diffraction is used to examine surface quality just prior to and after deposition. Uniform integral order diffraction streaks and fractional order reconstruction features observed from the Ge epilayers indicate that high quality Ge epitaxial layers can be grown using remote plasma-enhanced chemical-vapor deposition.

Notes: A 300 °C process has been used to deposit high-quality SiO2 on Si. The process is based on remote plasma-enhanced chemical vapor deposition. In this process excited species from a remote oxygen plasma interact with silane in the deposition zone. A hydrogen plasma is used to clean the silicon surface in situ just prior to deposition. After a 400 °C post-metallization anneal, interface-state densities as low as 3.7×1010 cm−2 eV−1 were measured with a fixed charge density of 2×1011 cm−2. The films exhibited good breakdown integrity, sustaining fields of 9–10 MV cm−1. The Si/SiO2 interface-state density directly correlates with the quality of reflection high-energy electron diffraction patterns from the silicon surface just prior to oxide deposition.

Notes: A novel insulator structure for gating of germanium surfaces has been developed. The structure consists of a very thin (on the order of 10 A(ring)) pseudomorphic silicon layer deposited on the germanium surface prior to deposition of a silicon dioxide insulating layer. Both the silicon and silicon dioxide layers were deposited at low temperature by remote plasma-enhanced chemical vapor deposition. Low interface state densities and surface inversion have been obtained for both n- and p-type germanium substrates. X-ray photoelectron spectroscopy and ion scattering spectroscopy analysis indicate that the thin pseudomorphic silicon layer provides complete silicon coverage of the germanium surface. The silicon layer protects the germanium surface from undesirable oxidation during the silicon dioxide deposition. The electrical properties of germanium metal-insulator-semiconductor structures which incorporated the silicon interlayer were much improved compared to structures in which the silicon dioxide was deposited directly on the germanium.

Notes: Diamond films grown by rf plasma-enhanced chemical vapor deposition in dilute CO, CF4, and CH4 (diluent H2) mixtures have been examined by cathodoluminescence (CL) in a transmission electron microscope to assess the incorporation of optically active impurities and defects. The details of the CL spectra are found to be dependent on the different gas mixtures and are correlated with the different film microstructures. Dislocation-related band A CL due to closely spaced donor-acceptor (D-A) pairs was observed from both the CO and CH4-grown films, but was absent in the CF4-grown material. Band A CL due to widely separated (D-A) pairs was seen in all samples but was especially dominant in the CF4-grown film. Emission due to a di-Si interstitial impurity was observed in CO- and CF4-grown films but was absent in the CH4-grown material.

Notes: Significant improvements in gating of Ge surfaces are achieved with the use of thin, pseudomorphic Si interlayers. Metal-insulator-semiconductor structures with mid-gap interface state densities of 5×1010 cm−2 eV−1 and showing no hysteresis have been realized on both n- and p-type Ge. The key elements of this technology are: surface cleaning, deposition of a thin Si interlayer, and the deposition of the gate dielectric, SiO2, all of which are performed in situ and sequentially at 300 °C in a single chamber with the remote plasma technique. Ion scattering spectroscopy shows complete coverage of the Ge surface by the Si layer. X-ray photoelectron spectroscopy shows the Si interlayer is about 18 A(ring) thick. The Si interlayer prevents the interfacial oxidation of the underlying Ge.

Notes: The role of chemisorbed hydrogen in the enhancement of low-energy electron emission from natural type IIb C(001) diamond surfaces has been investigated. A hydrogen induced low-energy emission peak, whose intensity was found to be a linear function of surface coverage, was observed. The direct observation of emission from vacuum level states in the photoemission spectra has determined a negative electron affinity of ∼0.4 eV for the hydrogenated C(001)-1×1 surface. Constant initial states photoemission has unambiguously identified the electron emission process with the escape of electrons from bulk electron states at the conduction-band minimum. © 1997 American Institute of Physics.

Notes: An apparent activation energy for CO desorption from (100) diamond surfaces exposed to atomic oxygen was determined by thermal desorption spectroscopy performed in ultrahigh vacuum and found to be equal to 45.0 kcal/mol. A minimum potential-energy reaction path was identified by semiempirical quantum chemical calculations. Starting with an O-on-top radical site, the reaction proceeds through a β-scission of the C—CO bond, formation of a dimer C—C bond, and finally cleavage of the second C—CO bond. The largest barrier along this pathway is that of the final desorption step; it is equal to 38.4 kcal/mol, in reasonable agreement with the experimental activation energy. Taken together, the broad experimental desorption-peak feature and the multitude of possible desorption sites with differing potential-energy barriers, suggests the existence of a distribution of CO sites on diamond surfaces.