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ABSTRACT: The mechanism of Schottky barrier formation on GaAs and other semiconductors seems to be getting more, rather than less, controversial. Therefore, it is important to examine new data as it becomes available. Four types of data will be mentioned. The emphasis will be on (1) the metal–GaAs chemical reaction products at the interface and their correlation (or lack thereof) with barrier heights and (2) the lack of evidence for discontinuity in Schottky barrier height as one goes from photoemission spectroscopy (PES) pinning results (thickness of order 1–1000 Å metal films). Also mentioned are (3) changes in barrier height for Al, Au, and Ag on diodes annealed up to 500 °C and (4) the effect on barrier height of growing ∼20 Å of native oxide on the GaAs before depositing a 1000‐Å metal layer. These data will be presented for discussion and evaluated in terms of the various models of Schottky barrier formation now under discussion which appear most consistent with the unified defect model.
Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 08/1985; · 1.34 Impact Factor
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ABSTRACT: Optically enhanced oxidation of GaAs is promising both for insight into fundamental mechanisms of oxygen chemisorption and for possible application in GaAs direct write. For atomically clean GaAs(110), we have found that sample temperature is a key parameter in determining the increase of oxygen uptake under low‐intensity argon ion laser illumination (1 W/cm<sup>2</sup> at 2.41 eV) relative to the ‘‘dark’’ uptake. Although cooling to 185 K suppresses the dark oxygen adsorption rate, the oxygen uptake with optical irradiation is the same at both 185 and 400 K. The ratio of laser‐assisted to dark uptake for 10<sup>8</sup> L exposure then approaches the enhancement necessary for spatially selective oxidation, showing an increase from 2.5 at room temperature to well over 10 at 185 K. After ruling out sample heating and direct oxygen gas excitation, we suggest that the light‐induced increase in uptake is due to electronic excitations in the GaAs. To explain the enhancement, one also needs to assume a weakly adsorbed precursor state that converts to the chemisorption state when thermally or optically activated; the implications for previously suggested oxidation mechanisms will be discussed.
Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 06/1985; · 1.25 Impact Factor
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ABSTRACT: Using valence‐band and core‐level photoemission spectroscopy (PES) and electrical device measurements, the effects of annealing Ag, Al, and Au on n‐type (110)GaAs Schottky diodes fabricated in ultrahigh vacuum have been studied. PES was used to monitor the annealing‐induced changes in the interface Fermi level position and the chemical nature of the metal–semiconductor interface for submonolayer and several monolayer coverages. Barrier height determinations were also performed using current–voltage (I–V) and capacitance–voltage (C–V) device measurements on annealed thick metal film metal–semiconductor junctions. The results of this study show that the annealing‐induced microscopic changes in the electronic and chemical structure of the metal–semiconductor interface can be strongly correlated with the macroscopic changes in the electrical properties of thick film metal–semiconductor Schottky diodes.
Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 06/1985; · 1.25 Impact Factor
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ABSTRACT: Using valence‐band and core‐level photoemission spectroscopy (PES) and electrical device measurements, the effects of annealing on Au:n‐type (110) GaAs Schottky diodes fabricated in ultrahigh vacuum have been studied. Similiar trends in the annealing‐induced changes in the barrier height of Au:n‐type GaAs were found for 0.2 and 15 monolayer coverages as determined by PES and for thick film coverages (1000 Å) as determined by current‐voltage (I‐V) and capacitance‐voltage (C‐V) measurement techniques. In each case, the barrier height was found to be stable for temperatures between 30 and 200 °C and between 300 and 500 °C; while a gradual decrease in the barrier height was found for annealing temperatures of 200–300 °C. These changes are correlated with the formation of a Au‐Ga rich layer at the interface during anneals at 200 to 300 °C. Leakage currents were found to dominate the I‐V characteristics in the devices which were annealed above the Au‐Ga eutectic temperature. These peripheral leakage currents were eliminated by mesa‐etching the devices. This allowed more reliable barrier height determinations using device measurements for higher annealing temperatures than has been previously reported for the Au‐GaAs system.
Journal of Applied Physics 03/1985; · 2.17 Impact Factor
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ABSTRACT: The room temperature chemical reactions of noble metals (Ag, Au, Cu), some transitions metals (Ni, Pd), and Al with the InP(110) surface have been studied using surface sensitive core level photoemission spectroscopy and photon beam excited Auger spectroscopy. It is shown that chemical reactions on InP are largely similar to the reactions of these metals with GaAs and Si surfaces. Metals that react with Si to produce phosphides also produce phosphides with similar types of chemical bonding. Silver overlayers give rise to the most abrupt interface with InP as is also the case for the nonreactive Ag–Si system. The kinetic limitations of the room temperature reaction and the types of overlayer growth are also considered.
Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 08/1984; · 1.34 Impact Factor
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ABSTRACT: The room‐temperature chemical reactions of noble (Cu, Ag, Au) and near‐noble transition (Ni, Pd) metals with the vacuum cleaved InP (110) surface have been studied with surface sensitive photoemission spectroscopies. It has been shown that the chemical reactions at these interfaces are closely similar to the reactions taking place on silicon substrates. In particular all metals that react strongly with Si to produce silicides (Cu, Ni, Pd) also form stable phosphides. This reaction is accompanied by phase segregation of metallic In. In addition, for Au (intermixing without a stable compound with P) and Ag (very weak reaction with substrate; growth of metallic Ag islands) the reactions with both InP and Si are qualitatively identical. It has been found that for GaAs the reactions with noble and near‐noble metals, though weaker than for InP, follow the same pattern.
Applied Physics Letters 07/1984; · 3.84 Impact Factor
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ABSTRACT: Palladium phosphide and phase segregated In are found to be produced by room temperature deposition of Pd on the atomically clean InP(110) face using soft x‐ray photoemission spectroscopy. The changes of the surface Fermi level position have been followed by subtracting the chemically shifted components from the In 4d and P 2p spectra. The value of the pinning position of ∼0.82 eV above the valence band maximum has been established. This result is compared with theoretical calculations of the surface defects in InP.
Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 05/1984; · 1.25 Impact Factor
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ABSTRACT: We present details of the interfacial chemical reactions and intermixing observed for Cu, Ag, and Au overlayers on the clean cleaved InP(110) surface using soft x‐ray photoemission spectroscopy (SXPS). Analysis of the P 2p and In 4d core levels and the P LVV Auger line reveals a range of chemical interactions: Cu–P metallic bonding with phase segregation of metallic In for Cu overlayers, Ag islanding with a small amount of In segregation for Ag overlayers, and elemental P precipitation with Au–In alloying for Au overlayers. Deconvolution of the substrate and reacted layer components of the core level spectra is used to determine the Fermi level pinning positions for Ag and Au on n‐ and p‐type InP, and these values are compared to theoretical calculations of native defect energy levels.
Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 05/1984; · 1.25 Impact Factor
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ABSTRACT: The room‐temperature growth of the Pd/n‐GaAs (110) intimate interface has been studied by soft x‐ray core level photoemission spectroscopy. It is shown that Pd reacts with the GaAs surface forming an arsenide compound in which phase segregated Ga metal is included. In addition some As is segregated on the surface of this composite. Using deconvolution of the different core level contributions, the Schottky barrier height of this system is experimentally determined to be 0.9±0.05 eV. The pinning is attributed to the deeper level of the unified defect model.
Applied Physics Letters 02/1984; · 3.84 Impact Factor
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ABSTRACT: The effect of placing controlled amounts of oxygen on the clean, cleaved (110) surface of GaAs before exposure to Au has been investigated with ultraviolet photoemission spectroscopy (UPS) and x‐ray photoemission spectroscopy (XPS). We studied: (a) the shape of the Ga‐3d level and changes of Ga (or As) intensity with oxygen and subsequent Au deposition; (b) the position of the Ga‐3d core level, with special regard to the surface or interface Fermi level (E fs ), as a function of oxygen and Au coverages; and (c) the valence band structure (where both oxygen and Au provide strong characteristic structure). For chemisorbed oxygen coverages of a small fraction up to 1 monolayer (ML) or above the Au:GaAs intermixing and E f shifts are significantly reduced. For the p‐type sample, after much less than 1 ML of oxygen, the maximum rise of E fs is suppressed as Au is added; after 10<sup>7</sup>L exposure E fs remains stationary until approximately 1 ML of Au is deposited; for high oxygen coverage (≥10<sup>8</sup>L), the oxygen appears to effectively retard the Au–GaAs interaction up to 10 ML of Au coverage. The width of the Ga‐3d core level increases monotonically with increased oxygen exposure. With 10<sup>1</sup><sup>0</sup>L exposure of oxygen, the Au coverage necessary to drop the Ga intensity to 1/e of its value on the oxidized surface is decreased to 4 ML, instead of 6 ML for the unoxidized surface. Supporting evidence from XPS spectra further demonstrates the intermixing is reduced between Au and GaAs by oxygen. The valence band structure shows the Au is dispersed on the oxidized surface. The results show that, for GaAs surfaces with a few tenths to above 1 ML of oxygen (before Au is deposited and with no annealing), the oxygen–GaAs interaction inhibits Au intermixing with GaAs. It causes a more abrupt interface than the case without oxygen.
Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 08/1983; · 1.34 Impact Factor
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ABSTRACT: A room temperature exchange reaction between an Al adsorbate and In atoms from the InP(110) surface has been observed during the early stages (∼0.5 to 5 Å) of interface formation by means of soft x‐ray photoemission spectroscopy of the Al 2p and In 4d core levels. As much as 8 Å of deposited Al was found to be required to slow down the transport of Al metal to the front of the reaction to the extent that an overlayer of nonreacted Al metal began to be observed on the surface. For all stages of barrier formation a segregation of In atoms, monitored by the chemical shift of the In 4d core lines, has been observed. A moderate heating (up to 200 °C) of a 12 Å deposition extends the exchange reaction deeper into the bulk. These results are discussed in the context of the widely studied Al–GaAs interface.
Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 08/1983; · 1.34 Impact Factor
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ABSTRACT: In this work we present a comparative study of the electronic and atomic structure of the interactive Cu/Si and Cu/InP interfaces. We use surface sensitive techniques, including soft x‐ray photoemission and photon‐ and electron‐induced Auger electron spectroscopy (AES), to show the strikingly similar chemical reactions and electronic properties at both interfaces. For both Cu/Si and Cu/InP, the valence band spectra and core level intensity profiles show intermixing of the metal with the substrate atoms. Moreover, for both semiconductors, the increase in Cu coverage induces an increase of the width of the Si L 2,3 VV (∼92 eV) and P L 2,3 VV (∼120 eV) Auger peaks at the earliest stage of barrier formation followed by a 4.4 eV splitting for higher coverages. These experimental observations lead to very similar models of the chemical reaction at the interface and the formation of the intermixed region and indicate bonding between Cu and P or Si for the InP and Si interfaces. In the case of the Cu/InP interface, we observe segregation of In to the surface and the formation of metallic islands.
Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 08/1983; · 1.34 Impact Factor
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ABSTRACT: Photoemission measurements are used to study the Schottky barrier formation and the intermixing (with GaAs) of the three metals, Cu, Ag, and Au, deposited at room temperature on GaAs(110) cleaved surfaces. It is tentatively concluded that Fermi level pinning cannot be followed satisfactorily for metal coverages above a monolayer. The work of Palau on Schottky barrier height (I–V and C–V) for Au and Ag deposited on cleaved GaAs(110) in UHV indicate pinning positions surprisingly close to those found for other overlayers in the ‘‘unified defect’’ model. It was found that ‘‘intermixing’’ between noble metals and GaAs decreases in the order of Cu, Au, and Ag. Although island formation probably occurs, it is tentatively concluded that the principle reason for difficulty in using our photoemission measurements to determine E fs for the noble metals is the inclusion of Ga (as well as As) in or on the noble metal overlayer.
Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 08/1983; · 1.34 Impact Factor
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ABSTRACT: We have performed soft x‐ray photoemission spectroscopy (SXPS) measurements, using synchrotron radiation as the excitation source, to study cleaved n‐type GaAs(110) surfaces covered with Au overlayers ranging in thickness from 0.3 monolayer (ML) to 80 ML. At room temperature our results show both band‐bending effects and significant Au intermixing, with a continuous, monotonic shift of the Au 4f core levels toward their bulk positions with increasing Au coverage. Observation of the Ga 3d and As 3d core levels indicates a preferential As segregation to the surface at the highest Au coverages. The effect of heating (up to 500 °C) on a relatively thick (15 ML) Au overlayer has been studied using valence band as well as core level emission. These results indicate an increase in the Ga and As concentrations with evidence of metallic Ga formation. These findings have an important bearing on our understanding of Schottky barrier formation as well as the particular behavior of the Au–GaAs interface.
Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 05/1983; · 1.25 Impact Factor
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ABSTRACT: We report new photoemission studies of the Au–InP (110) interface for both n‐ and p‐type samples using synchrotron radiation in the energy range 80 to185 eV. By slowly increasing Au coverages and by studying core level structures and valence band spectra we have been able to differentiate between two coverage intervals. The lower coverage interval (θ≪1 ML) is dominated by band bending with no measurable chemical changes and with a total measured Schottky barrier height of 0.6 eV. In the higher coverage interval (1≪θ≤37 ML), we observed changes in the In 4d and P 2p core level shapes and a monotonic shift of the Au 4f to lower binding energies with increased Au coverage. Evidence of intermixing of Au with the P and In atoms indicates the formation of a nonabrupt interface. These results are at variance with the view that Au is a nonreactive metal on InP (110).
Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 05/1983; · 1.25 Impact Factor
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ABSTRACT: Considerable interest in the use of laser irradiation as a means of processing (annealing, cleaning, alloying, etc.) semiconductor materials, as well as the importance of the oxygen surface chemistry on III‐V semiconductors, has led us to study the effect of low‐intensity (?3 W/cm<sup>2</sup>) laser radiation on the oxidation behavior of (110) surfaces of GaAs cleaved in UHV (≪10<sup>-10</sup> Torr). The oxygen sticking probability in the submonolayer coverage range has been increased by a factor of 10<sup>3</sup> (from a probability of ∼10<sup>-9</sup> to ∼10<sup>-6</sup>) by uniform irradiation of the GaAs surface with a continuous wave Ar<sup>+</sup> laser (λ = 5145 Å) during the oxygen exposure. We find the data cannot be explained in terms of either heating of the surface or excitation of the oxygen by the laser radiation; it appears that the most likely explanation of the phenomena is an increase in the density of electrons and/or holes at the surface. A limiting step in the oxygen uptake process is the breakup of the oxygen molecule; this dissociation would be increased by increasing the number of electrons at or near the surface. In chemical terms, the reconstructed GaAs surface has no orbitals suitable for binding oxygen—such orbitals can be provided by changing the charge state of a surface atom via optical excitation.
Journal of Vacuum Science and Technology 08/1982;
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ABSTRACT: New photoemission measurements show higher Schottky barrier heights (≳1.3 eV) on atomically clean GaAs(110) surfaces at a Au coverage of about 25 monolayers. It is suggested that this effect is due to the movement of Au into the semiconductor; at room temperature it creates acceptor states near the valence band maximum (VBM) that cause the Fermi level at the surface (E fs ) to move close to the VBM. We found that heating of the GaAs(110) surface (above 100 °C) covered with a small amount of Au (0.2 monolayer) causes E fs to move back to its original position (on the clean surface before Au deposition). The heating process is found to greatly inhibit the formation of large barrier heights due to the removal of defect states from the surface region.
Journal of Vacuum Science and Technology 08/1982;
