Fermi Level Depinning on n-Epitaxial GeSn by Yb Stanogermanide Formation With Low-Contact Resistivity

Teng, Shih-Chieh; Su, Cheng‐Kuan; Chen, Kuen-Yi; Chou, Chun‐Nan; Wu, Yung-Hsien

doi:10.1109/led.2016.2591620

Cited by 7 publications

(2 citation statements)

References 19 publications

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“…For high-performance applications, low series resistances such as source/drain (S/D) and contact resistances are needed. While a low contact resistivity of <10 –9 Ω·cm 2 has been demonstrated in a metal/p-GeSn contact, for metal/n-Ge(Sn) contacts, their high electron Schottky barrier height (SBH) due to Fermi-level pinning (FLP) leads to a large contact resistivity of 10 –6 –10 –7 Ω·cm 2 . , Because of a large number of surface states in Ge(Sn), the Fermi level is pinned near the valence band edge, resulting in a high SBH for electrons. , Understanding the SBH properties of the metal/n-GeSn contacts is critical to reduce the contact resistivity, and only few studies were reported on the electron SBHs. − In those studies, the electron SBHs were obtained from the metal/n-GeSn contacts with low Sn fractions (0–3.4%), or they were indirectly extracted from the hole SBHs. , Ideally, the electron SBH is equal to the energy difference between the band gap and the hole SBH. The band gap energy needs to be determined precisely to extract the electron SBH.…”

Section: Introductionmentioning

confidence: 99%

“…While a low contact resistivity of <10 −9 Ω•cm 2 has been demonstrated in a metal/p-GeSn contact, 3 for metal/n-Ge(Sn) contacts, their high electron Schottky barrier height (SBH) due to Fermi-level pinning (FLP) leads to a large contact resistivity of 10 −6 −10 −7 Ω•cm 2 . 4,5 Because of a large number of surface states in Ge(Sn), the Fermi level is pinned near the valence band edge, resulting in a high SBH for electrons. 6,7 Understanding the SBH properties of the metal/n-GeSn contacts is critical to reduce the contact resistivity, and only few studies were reported on the electron SBHs.…”

Section: Introductionmentioning

confidence: 99%

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Schottky Barrier Height Modulation of Metal/n-GeSn Contacts Featuring Low Contact Resistivity by in Situ Chemical Vapor Deposition Doping and NiGeSn Alloy Formation

Chuang

Liu

Kao

et al. 2021

ACS Appl. Electron. Mater.

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GeSn complementary metal-oxide-semiconductor (CMOS) devices have attracted much attention for future VLSI technology nodes due to high carrier mobility. However, Fermilevel pinning in metal/n-GeSn contacts leads to high contact resistivity and limits GeSn CMOS devices for high-performance logic applications. In this work, we investigate Schottky characteristics and contact resistivity in the metal/n-GeSn contacts. Highquality n-GeSn layers were epitaxially grown by chemical vapor deposition with an in situ doping technique with a high carrier activation rate of 73% up to a doping concentration of ∼1.3 × 10 20 cm −3 . The electron Schottky barrier heights of the metal/n-GeSn contacts with different Sn fractions and metal work functions were extracted by an I−T method. The results show that the Fermi level is pinned at an energy level slightly above the valence band maximum. The Schottky barrier height is highly correlated with the GeSn band gap energy and decreases with the Sn fraction. The contact resistivity of the metal/n-Ge 0.9 Sn 0.1 contacts was extracted by a refined transmission line model and effectively reduced by increasing the doping concentration in the n-GeSn films. A post-metal annealing step at 400 °C was performed to further reduce the Schottky barrier height by forming NiGeSn alloys. A record low contact resistivity of ∼1.5 × 10 −7 Ω•cm 2 is achieved without any surface treatment. This is attributed to the reduced Schottky barrier height by increasing the Sn fraction in the n-GeSn film and the reduced Schottky barrier width due to the high carrier density achieved by in situ doping.

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