M. J. Mantini

In situ cleaning of GaAs surfaces using hydrogen dissociated with a remote noble-gas discharge

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.

The role of atomic hydrogen and its influence on the enhancement of secondary electron emission from C(001) surfaces

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.

SECONDARY ELECTRON EMISSION ENHANCEMENT AND DEFECT CONTRAST FROM DIAMOND FOLLOWING EXPOSURE TO ATOMIC HYDROGEN

Polished nominal (100) surfaces of four types of diamonds were exposed to atomic hydrogen by hot filament cracking of H2 gas or by immersion in a H2 plasma discharge. Both types IIa and IIb (100) diamond surfaces exhibited the following characteristic changes: (a) secondary electron (SE) yield increased by a factor of ∼30 as measured in a scanning electron microscope (SEM), (b) near‐surface, nontopographical defects were observable directly using the conventional SE mode of the SEM, (c) surface conductance increased by up to 10 orders of magnitude. These changes were observed only weakly in nitrogen‐containing types Ia and Ib diamonds.

The role of an ultrathin silicon interlayer at the SiO2‐Ge interface

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) 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 of the SiO2 film is established by x‐ray photoelectron spectroscopy (XPS). Throughout a cumulative series of thin (∼10 A) oxide depositions, XPS showed no evidence of Ge oxidation st...

Epitaxial silicon deposition at 300 °C with remote plasma processing using SiH4/H2 mixtures

Epitaxial Si films have been deposited on Si(100) at 300 °C by remote plasma‐enhanced chemical vapor deposition using SiH4/H2 mixtures with deposition rates as high as 25 A/min at these low temperatures. Hall measurements of the film show an unintentional doping level of about 1×1017 cm−3 with electron mobilities of 700 cm2 V−1s−1. Critical to the process is the in situ cleaning of the silicon substrate surface prior to deposition.

Interface engineering with pseudormorphic interlayers: Ge metal‐insulator‐semiconductor structures

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 thick. The Si interlayer prevents the interfacial oxidation of the underlying Ge.

Influence Of Surface Terminating Species On Electron Emission From Diamond Surfaces

Changes in electron affinity on the C(001) surface of type Ifb diamonds have been studied using a variety of surface analytical techniques, including ultraviolet photoemission spectroscopy, secondary electron emission spectroscopy and constant initial states photoemission. Following H-plasma exposure, an intense low-energy emission peak was observed with all spectroscopies. The emission intensity associated with the chemisorbed hydrogen was found to be a linear function of surface hydrogen coverage. The proposed mechanism for the hydrogen induced changes in electron affinity is the creation of a dipole on the surface by the addition of hydrogen which opposes the surface potential of the bare surface. A total change in electron affinity of 2.2 eV was measured upon hydrogen termination of the clean 2x1 surface. Constant initial states photoemission demonstrates that the intense low-energy electron emission observed arises from electrons emitted from bulk states at the conduction band edge. Oxygen, as an electronegative species, was found to have the opposite effect and the electron affinity was increased by ∼3.7 eV upon oxygen termination relative to the clean 2x I surface.

Electronic Structure of Polycrystalline PECVD Diamond Surfaces

Ultraviolet and X-ray photoelectron spectroscopy techniques have been employed in a preliminary study of the electronic structure of polycrystalline diamond films that have been grown on Si substrates by if-plasma enhanced chemical vapor deposition using water/ethanol growth chemistries. In particular, polycrystalline diamond films with distinctly different surface morphologies and Raman scattering characteristics have been investigated. Corresponding ultraviolet photoemission spectra from air-exposed samples have shown the presence of a prominent low-energy secondary electron emission peak indicative of a negative electron affinity (NEA) surface. Chemical stability of the polycrystalline diamond NEA surface has been demonstrated following conventional acid cleans and hydrogen plasma processing. In contrast, an oxygen (20%)/Ar plasma exposure has been shown to extinguish the photoemission of low-energy secondary electrons and remove the NEA. However, by employing a high-temperature anneal at 750 °C for 15 min in ultra-high vacuum the NEA surface can be restored. Compared to NEA single crystal diamond surfaces the photoexcited low-energy electron emission from chemical vapor deposited polycrystalline diamond films is more robust.

Heteroepitaxy and characterization of Ge‐rich SiGe alloys on GaAs

Growth of SiGe alloys on GaAs substrates at temperatures as low as 590 °C is described. The growth has been accomplished using the pyrolysis of disilane (Si2H6) and germane (GeH4) at such temperatures. The layers were characterized electrically and show n‐type conduction with carrier concentrations of ∼1×1018 cm−3. The high quality of the SiGe layers is evident in the Rutherford‐backscattering/channeling results on SiGe/GaAs structures. A χmin of 5.6% has been obtained for a Si0.05Ge0.95 layer on GaAs. χmin increases with increasing silicon content in the SiGe layers. The SiGe alloy layers were also studied by x‐ray diffraction, and the composition was determined assuming coherent, tetragonally distorted growth of SiGe on GaAs. The distortion calculations, based on theoretical elastic constants, were confirmed using Auger electron spectroscopy to determine alloy composition.

Epitaxial growth of Cu-Ni Single Crystal Alloys and Multilayers by Molecular Beam Epitaxy

Epitaxial growth of thin films, alloys, and multilayers from the Cu-Ni system are being explored as a means of fabricating a substrate to lattice match diamond. These single crystal films are superior to commercially available substrate material. Due to the high reactivity of the metal surfaces in atmosphere, all processing must be done under UHV conditions. In vacuo preparation, growth, and analysis of the metals is described.