Photoemission surface core-level study of sulfur adsorption on Ge(100)

Weser, T.; Bogen, A.; Konrad, B.; Schnell, R.D.; Schug, C.; Steinmann, and W.

doi:10.1103/physrevb.35.8184

Cited by 116 publications

(68 citation statements)

References 16 publications

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“…On the other hand, the adsorption of the group-V elements As and Sb leads to formation of symmetric adatom dimers on Si(001) and Ge(001) [3][4][5]. S monolayers are found to passivate the Ge(001) surface and yield an almost ideal (1 x 1) structure [6]. The same behavior has been reported for Se on Si(001) [7].…”

mentioning

confidence: 51%

Theory of adsorption: Ordered monolayers from Na to Cl on Si(001) and Ge(001)

Krüger

Pollmann

1994

Appl. Phys. A

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Abstract. First principles calculations of clean and adsorbate-covered surfaces of Si(001) and Ge(001) are reported. Chemical trends in the adsorption of ordered Na, K, Ge, As, Sb, S, Se and CI overlayers are discussed. The calculations are based on the local-density approximation and employ non-local, norm-conserving pseudopotentials together with Gaussian orbital basis sets. The semi-infinite geometry of the substrate is properly taken into account by employing our scattering theoretical method. From total-energy minimization calculations we obtain optimal surface reconstructions which show asymmetric dimers for Si(001), Ge(001) and Ge:Si(001). For As:Si(001), Sb:Si(001) and Sb:Ge(001), we find symmetric adatom dimers in the equilibrium geometries. S or Se adlayers are found to be adsorbed in bridge positions forming a (1 x 1) unit cell with a geometry very close to the configuration of a terminated bulk lattice. C1 atoms adsorb on top of the dangling bonds of symmetric Si dimers residing in the first substrate-surface layer. Our calculations for Na:Si(001) and K:Si(001) confirm valleybridge site adsorption for half monolayer coverage. For full monolayer alkali-metal coverage, adsorption in pedestal and valley-bridge positions is found to be energetically most favourable. The calculated optimal adsorption configurations are in excellent agreement with a whole body of recent experimental data on surface-structure determination. For these structural models, we obtain electronic surface band structures which agree very good with a wealth of data from angle-resolved photoemission spectroscopy investigations. The adsorption of adlayers at semiconductor surfaces has been under intensive study in recent years. These investigations are motivated by fundamental physical reasons and important technological applications. In basic research, semiconductors are interesting substrates for adsorption systems due to the unsaturated directional bonds at their surfaces. This allows the formation of chemical compounds which are neither stable as small, isolated molecules nor as extended solids. The technological interest ranges from homoand heteroepitaxy and growth, via surface passivation and doping to dry etching and photo-surface cleaning. For example, the quality of the heteroepitaxial growth of GaAs on Si is determined by the initial stage of this process which consists in formation of As adlayers. Furthermore, surface passivation may involve As, S or Se atoms. In the fabrication of electronic devices, dry etching and photo-surface cleaning is carried out by the reaction of C1 on Si. The adsorption of alkali metals in the range of monolayer coverage leads to a drastic reduction of the ionization energy. These systems have important applications as high-efficiency emitters. They are also widely discussed in the context of the Schottky-barrier problem [1].

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confidence: 51%

Theory of adsorption: Ordered monolayers from Na to Cl on Si(001) and Ge(001)

Krüger

Pollmann

1994

Appl. Phys. A

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“…A coverage of 0.3 monolayers (MLs) of sulfur was obtained, and the sulfur atoms were in two-fold bridging sites shared between two germanium atoms. 5,6 Alternate sources of sulfur such as H 2 S have also been investigated. Gas phase H 2 S dissociatively adsorbs on the surface and reaches a saturation coverage of 0.25 ML at room temperature and up to 0.5 ML after heating to 553 K to desorb hydrogen from the surface.…”

Section: Introductionmentioning

confidence: 99%

Reaction of aqueous ammonium sulfide on SiGe 25%

Heslop

Peckler

Muscat

2017

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

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SiGe 25% substrates were treated with aqueous solutions of ammonium sulfide with and without added acid to understand the adsorption of sulfur on the surface. X-ray photoelectron spectroscopy showed no sulfide layer was deposited from aqueous (NH 4 ) 2 S alone and instead both Si and Ge oxides formed during immersion in the sulfur solution. The addition of hydrofluoric and hydrochloric acids dropped the pH from 10 to 8 and deposited sulfides, yet increased the oxide coverage on the surface and preferentially formed Ge oxides. The sulfur coverage grew with increasing concentrations of acid in the aqueous (NH 4 ) 2 S. The simultaneous deposition of O and S is suspected to be the result of oxidized sulfur species in solution. Metal-insulator-semiconductor capacitor (MISCAP) devices were fabricated to test the electrical consequences of aqueous ammonium sulfide wet chemistries on SiGe. MISCAPs treated with acidic ammonium sulfide solutions contained fewer interface defects in the valence band region. The defect density (D it ) was on the order of 10 þ12 cm -2 eV À1. The flat band voltage shift was lower after the acidic ammonium sulfide treatment, despite the presence of surface oxides. Adsorption of S and potentially O improved the stability of the surface and made it less electrically active.

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“…[3][4][5][6] or by reactions in the gas phase using H 2 S or elemental S. 2,[7][8][9][10] Both treatments result in the adsorption of S on the Ge surface. However, the amount of adsorbed S, as well as the surface ordering can differ.…”

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confidence: 99%

“…The surface ordering reported for the wet (NH 4 ) 2 S treatment is a (1 Â 1) reconstruction, 3,5 while the gas phase reaction of H 2 S results in a (2 Â 1) reconstruction 2,9 and the gas phase adsorption of elemental S in a (1 Â 1) reconstruction. 7,8 The exact coverage of S on the Ge surface after the (NH 4 ) 2 S treatment varies for different reports. Lyman et al 4 ) measured the S coverage by XRF (2-3 monolayers) and the coherent coverage by X-Ray Standing Waves ($ 0.4 monolayers), the latter being defined as the total number of S atoms in registry with the Ge substrate.…”

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confidence: 99%

Atomic Layer Deposition of High-κ Dielectrics on Sulphur-Passivated Germanium

Sioncke

Lin

Brammertz

et al. 2011

J. Electrochem. Soc.

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High mobility channels are currently being explored to replace the silicon channel in future CMOS technology nodes. However, until now the promising bulk properties are very difficult to translate into high transconductance due to a poor passivation of the interface between the gate dielectric and the channel. We have studied the S-passivation of the germanium surface combined with various high-permittivity dielectric gate stacks. (NH4)2S is used to achieve a S-terminated Ge surface. We found that the Ge/S/Al2O3 interface is superior to both the Ge/S/ZrO2 and Ge/S/HfO2 interfaces. Bi-layer stacks consisting of Ge/S/Al2O3/HfO2 or Ge/S/Al2O3/ZrO2 were built to achieve a gate stack with low EOT (Equivalent Oxide Thickness). In these bi-layer stacks, the Al2O3 thickness is reduced to a minimum without degradation of the interface properties. Rather thick Al2O3 interlayers (∼ 2 nm) are needed due to island growth on S-terminated Ge surface. A pMOSFET was built using a bi-layer gate stack (Ge/S/Al2O3/HfO2). The peak mobility of this device is > 200 cm2/Vs at an EOT of 1.5 nm.

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Photoemission surface core-level study of sulfur adsorption on Ge(100)

Cited by 116 publications

References 16 publications

Theory of adsorption: Ordered monolayers from Na to Cl on Si(001) and Ge(001)

Theory of adsorption: Ordered monolayers from Na to Cl on Si(001) and Ge(001)

Reaction of aqueous ammonium sulfide on SiGe 25%

Atomic Layer Deposition of High-κ Dielectrics on Sulphur-Passivated Germanium

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