C. W. Wilmsen

The C KLL first‐derivative x‐ray photoelectron spectroscopy spectra as a fingerprint of the carbon state and the characterization of diamondlike carbon films

The C KLL spectra from natural diamond, graphite, and single‐crystal β‐SiC have been investigated using x‐ray photoelectron spectroscopy and first‐derivative x‐ray excited Auger electron spectroscopy (XAES). It is shown that the XAES spectra is essentially the same as that obtained with conventional AES with the added benefits of no electron beam (e‐beam) damage, enhanced fine structure, and the simultaneous acquisition of the C 1s and valence‐band spectra. The C KLL XAES fine structure provides a fingerprint of the carbon bonding state and the C 1s and valence‐band spectra provide insight into the origin of this fine structure. Diamondlike carbon films fabricated by hydrogen gas reactive sputtering of graphite on Si were also investigated. The XAES C KLL spectra in conjunction with the valence‐band spectra verifies the tetrahedral C–C bonding in these films even though the AES spectra shows a graphitelike structure; indicative of e‐beam damage.

Comparison of the CKLL first-derivative Auger spectra from XPS and AES using diamond, graphite, SiC and diamond-like-carbon films

Abstract The carbon KLL first-derivative Auger spectra obtained by numerically differentiating the XPS N(E) line gives a better fine-structure fingerprint of the carbon state than conventional AES. The first-derivative of the X-ray excited (XAES) CKLL spectrum from a diamond-like-carbon (DLC) film exhibited almost the same spectrum as both the XAES and AES spectra from natural diamond. However, the AES spectrum of the DLC film indicated a graphite-like structure due to electron beam damage. Comparison of the XAES and AES spectra suggested that the electron beam used in conventional AES partially changed the plasmon loss structure of carbon in diamond, graphite and β-SiC as well.

The operation of the semiconductor‐insulator‐semiconductor solar cell: Experiment

We have reported on the theory of semiconductor‐insulator‐semiconductor (SIS) solar cells in a previous publication. In this paper, the fabrication and properties of indium tin oxide/p‐Si single‐crystal solar cells will be described. The ITO is deposited by the ion‐beam sputtering method. Best photovoltaic devices are obtained when the composition of indium tin oxide (ITO) is 91 mole% and 9 mole% SnO2. The device properties as a function of the ITO composition will be described. The thickness and the composition of the oxide‐silicon interface is critical for device performance. The existence of a thin interfacial layer is demonstrated by Auger spectroscopy. The effect of temperature on device performance and the spectral response are compared with the theory. The SIS model accurately matches the major trends observed in experimental nITO/p‐Si solar cells.

Thermal oxidation of InP

The growth rate and chemical composition of thermally grown oxides on InP in dry oxygen are presented. The oxide is found to grow very slowly below 340 °C and rapidly above this temperature. All the oxides grown in the temperature range 340–450 °C are composed of approximately 70%–75% In2O3 and 25%–30% P2O5. There is also some evidence for low concentrations of another bonding state of phosphorous.

Oxide layers on III–V compound semiconductors☆

Abstract Results of an investigation of the thermal and anodic oxidation of the III–V compound semiconductors are presented. First the growth models for the thermal oxidation of metals and alloys are reviewed. From these, a model for the growth of thermal oxides on the III–V compounds is proposed. It is shown that the diffusion rates of the elements, the mutual solubilities of the mixed oxides and the thermodynamic stabilities of the oxides are important factors in the oxide growth. Auger compositional profiles of the thermal oxides show that some oxides partition into two layers while others are nearly uniform. The insulating properties of these oxides are shown to be related to the chemical composition. The Auger profiles of the anodic oxides are contrasted with those of the thermal oxides.

Auger analysis of ultrathin SiO2 layers on silicon

The Auger LVV lines of ultrathin SiO2 layers thermally grown on Si are analyzed by comparing the measured lines with lines synthesized from standard SiO2 and Si lines. The synthesized lines were corrected for ion and electron beam effects and charging. The synthesis technique provides quantitative interpretation of the Auger lines in the interfacial region. An apparent thickness‐dependent transition region is observed which can be explained as either a graded SiO2‐Si region or as an abrupt SiO2‐Si transition with a nonuniformly thick oxide. The latter is the more probable.

Reaction between SiC and W, Mo, and Ta at elevated temperatures

The stability of W, Mo, and Ta in contact with single‐crystal β‐SiC at elevated temperatures has been investigated using Auger sputter profiling. All three metals were found to form a thin‐mixed layer of metal carbide and silicide upon metal deposition at room temperature. This layer is thought to be the result of surface defects which weaken the Si—C bonds and allow a low‐temperature reaction to occur. Upon heating, the Ta readily reacts with the SiC substrate and forms a mixed layer of Ta carbide and silicide at annealing temperatures as low as 400 °C, however, the W/SiC and Mo/SiC systems are stable and change very little after annealing at 850 and 800 °C, respectively.

Characterization of β‐SiC surfaces and the Au/SiC interface

The chemistry of the β‐SiC surface has been studied with Auger electron spectroscopy (AES) and x‐ray photoemission spectroscopy (XPS). The chemically etched surface was found to be nearly stoichiometric, with only a small amount of adsorbed oxygen, which appears to be localized on the Si states. Ion sputtering caused the surface to become Si rich. Compared to Si, the β‐SiC surface was very resistant to oxidation by air exposure at room temperature and when annealed in O2 at 300 °C. In addition, essentially no reaction occurred between Au and etched β‐SiC even after extensive heat treatment.

Initial oxidation and oxide/semiconductor interface formation on GaAs

Evolution of the oxide/GaAs interface formation for both thermal and anodic oxides is presented. This is accomplished by examining ESCA profiles of 21–85 A thick thermal and anodic oxides. The anodic oxide begins with a nucleation and growth process during which the As oxides are leached out leaving a continuous layer of Ga2O3. Oxide growth then proceeds by Ga and As diffusion to the surface where they oxidize leaving the inner layer of Ga2O3 unchanged. Thus the anodic oxide/GaAs interface is formed during the first 40 A of oxide growth. During thermal oxidation both Ga2O3 and As2O3 are formed but the As2O3 evaporates rapidly leaving the Ga2O3. Once the Ga2O3 layer is formed, the As is excluded from entering the continuous Ga2O3 layer and collects at the oxide/GaAs interface. This occurs after about 40 A of oxide growth.

Analysis of the oxide/semiconductor interface using Auger and ESCA as applied to InP and GaAs

This paper compares the Auger and ESCA techniques used to characterize the interfaces of thermally grown and anodic oxides of InP and GaAs. In the anodic oxide of GaAs, the Ga–O bonding extends deeper into the GaAs than the As–O bonding. In the anodic oxide of InP, both the P–O and In–O bonding penetrate to the same depth. The anodic oxide–GaAs interface changes with electrolyte. There is elemental P at the interface of the thermal oxide on InP, but it was not possible to prove or disprove the existence of elemental As at the anodic oxide/GaAs interface. It was found that the ESCA technique provided much needed bonding information which greatly facilitates characterizing the interface. It appears essential that both composition and bonding be determined.