Fermi-level pinning and charge neutrality level in germanium

Dimoulas, A.; Tsipas, Polychronis; Sotiropoulos, A.; Evangelou, E. K.

doi:10.1063/1.2410241

Cited by 588 publications

(422 citation statements)

References 20 publications

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“…However, the Fermi level is almost perfectly pinned to the valence band edge of Ge at the metal=Ge interface for various element metals. 7,8) This fact suggests that the Fermi level pinning (FLP) on Ge may be limited by an intrinsic mechanism. Therefore, understanding the FLP mechanism and controlling the SBH on n-Ge are strongly required.…”

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confidence: 99%

Reexamination of Fermi level pinning for controlling Schottky barrier height at metal/Ge interface

Nishimura

Yajima

Toriumi

2016

Appl. Phys. Express

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The element metal/germanium (Ge) interface exhibits a strong Fermi level pinning (FLP), which is usually characterized on the basis of Ge side semiconductor properties. In this work, we demonstrate that metal properties significantly affect the Schottky barrier height (SBH) on Ge. Metallic germanides show both FLP alleviation and a clear substrate orientation dependence of SBH on Ge, despite the nearly perfect FLP and very slight orientation dependence in the element metal case. As a result, ohmic characteristics are observed at germanide/n-Ge (111) junctions. The metal properties required to alleviate the FLP on Ge are also discussed. © 2016 The Japan Society of Applied Physics G ermanium (Ge) is one of the promising semiconductor materials for high-performance complementary metal-oxide-semiconductors (CMOSs) in the next generation owing to its high electron and hole mobilities. Recently, high electron mobility in Ge n-channel metal-insulation-semiconductor field-effect transistors (n-MISFETs) with a sub-nm equivalent oxide thickness gate stack has been demonstrated, owing to appropriate gate stack designing, [1][2][3][4] in addition to the high hole mobility in Ge p-MISFET, which has already been reported. 5,6) Therefore, the most serious challenges for realizing practical scaled Ge CMOS are currently the reduction in parasitic resistance and the suppression of off-state leakage at the source=drain of MISFETs. In particular, to reduce the contact resistance at the metal=Ge interface, a reduction in Schottky barrier height (SBH) at the interface is definitely required. However, the Fermi level is almost perfectly pinned to the valence band edge of Ge at the metal=Ge interface for various element metals. 7,8) This fact suggests that the Fermi level pinning (FLP) on Ge may be limited by an intrinsic mechanism. Therefore, understanding the FLP mechanism and controlling the SBH on n-Ge are strongly required.Recently, FLP alleviation has been demonstrated in ultrathin-film [GeO 2 , 9) Al 2 O 3 , 9) GeN, 10) SiN,11) MgO,12) Si,13) ZnO, 14) TiO 2 , 15) W-encapsulating Si, 16) indium tin oxide (ITO) 17) ] insertion at the element metal=Ge interface. When the direct metal=Ge interface is replaced by the metal= ultrathin film and ultrathin film=Ge interfaces, the strong FLP at the direct metal=Ge interface becomes less significant. Nevertheless, since the interface layer resistance is added, the direct metal=Ge interface with a low SBH is more preferable from the viewpoint of contact resistance reduction. With respect to the direct metal=Ge interface, it has recently been reported that the SBHs at epitaxial Fe 3 Si, 18) α-TiGeN, 19) epitaxial Mn 5 Ge 3 , 20) epitaxial NiGe 2 , 21) graphene, 22) and Sn 23) =n-Ge interfaces are relatively low, which deviates from the trend of strong FLP. 7,8) Some of them 18,20,21,23) considered that the FLP on Ge might not be determined by an intrinsic but extrinsic origin. It is inferred that those two kinds of experimental results may include a key aspect to understand the FLP mechani...

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mentioning

confidence: 99%

Reexamination of Fermi level pinning for controlling Schottky barrier height at metal/Ge interface

Nishimura

Yajima

Toriumi

2016

Appl. Phys. Express

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“…A thin Al layer (~4 nm) was formed without breaking the vacuum after the Py deposition in order to prevent oxidation of the Py surface. It is worth noting that the Py/p-type Ge contact is ohmic because of Fermi level pinning 13,14 and that dynamical spin injection is not impeded by the Schottky barrier. In order to inject spins dynamically, we employed a spin pumping method using an electron spin resonance (ESR) system.…”

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Dynamical Spin Injection into p-Type Germanium at Room Temperature

Koike

Shikoh

Ando

et al. 2013

Appl. Phys. Express

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“…In analogy with Si, an important role in determining Ge surface properties is played by the dangling bond (DB). Both theoretical and experimental arguments [8][9][10] indicate that the Ge DB is a charge trapping center responsible for the density of states at the interface between Ge and oxides and possibly for the Fermi level pinning. Despite its impact, little is known on the microstructure of the DB at the Ge/ oxide interface.…”

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Evidence of Trigonal Dangling Bonds at the Ge(111)/Oxide Interface by Electrically Detected Magnetic Resonance

Paleari

Baldovino²,

Molle³

et al. 2013

Phys. Rev. Lett.

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Despite a renewed interest in Ge as a competitor with Si for a broad range of electronic applications, the microstructure and the electronic properties of the dangling bonds that, in analogy with Si, are expected at the Ge/oxide interface have escaped a firm spectroscopy observation and characterization. Clear evidence based on contactless electrically detected magnetic resonance spectroscopy of a dangling bond at the Geð111Þ=GeO 2 interface is reported in this Letter. This result supports the similarity between dangling bonds at the Si(111)/oxide and Ge(111)/oxide interfaces, both showing C 3v trigonal point symmetry with the main axis oriented along the h111i direction. In contrast, at the Ge(001)/oxide interface the absence of the trigonal center in favor of a lower symmetry dangling bond marks the difference with the Si(001)/ oxide interface, where both centers are present and the one having higher point symmetry prevails. This fact is rationalized in terms of suboxide interface rearrangement and oxide viscoelasticity, which promote the generation of the nonaxial centers at distorted dimers. The unambiguous identification of the centers at the Ge/oxide interfaces yields a deeper insight into the physical properties of the suboxide interface structure and offers a valid indicator for the evaluation of different surface capping and passivation techniques, with the potential to boost the Ge-related technology.

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Fermi-level pinning and charge neutrality level in germanium

Cited by 588 publications

References 20 publications

Reexamination of Fermi level pinning for controlling Schottky barrier height at metal/Ge interface

Reexamination of Fermi level pinning for controlling Schottky barrier height at metal/Ge interface

Dynamical Spin Injection into p-Type Germanium at Room Temperature

Evidence of Trigonal Dangling Bonds at the Ge(111)/Oxide Interface by Electrically Detected Magnetic Resonance

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