Schottky barrier tuning <i>via</i> dopant segregation in NiGeSn-GeSn contacts

Schulte-Braucks, C.; Hofmann, Emily V. S.; Glass, Stefan; Driesch, Nils von den; Mußler, Gregor; Breuer, U.; Hartmann, Jean‐Michel; Zaumseil, P.; Schrøder, Thomas B.; Zhao, Qing‐Tai; Mantl, S.; Buca, D.

doi:10.1063/1.4984117

Cited by 21 publications

(16 citation statements)

References 42 publications

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“…Moreover, Pt–GeSn showed better behavior in terms of thermal stability compared to Ni–GeSn and Ti–GeSn. Because Sn loss occurs during B-doped GeSn CVD growth, it is still challenging to create low contact resistivity p-type GeSn contacts with high Sn contents, a challenge that is particularly critical for GeSn lasers and GeSn TFETs [ 207 , 208 ].…”

Section: Research Progress For Gesn Cvd Growth and Its Potential Applicationsmentioning

confidence: 99%

Review of Si-Based GeSn CVD Growth and Optoelectronic Applications

et al. 2021

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GeSn alloys have already attracted extensive attention due to their excellent properties and wide-ranging electronic and optoelectronic applications. Both theoretical and experimental results have shown that direct bandgap GeSn alloys are preferable for Si-based, high-efficiency light source applications. For the abovementioned purposes, molecular beam epitaxy (MBE), physical vapour deposition (PVD), and chemical vapor deposition (CVD) technologies have been extensively explored to grow high-quality GeSn alloys. However, CVD is the dominant growth method in the industry, and it is therefore more easily transferred. This review is focused on the recent progress in GeSn CVD growth (including ion implantation, in situ doping technology, and ohmic contacts), GeSn detectors, GeSn lasers, and GeSn transistors. These review results will provide huge advancements for the research and development of high-performance electronic and optoelectronic devices.

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Section: Research Progress For Gesn Cvd Growth and Its Potential Applicationsmentioning

confidence: 99%

Review of Si-Based GeSn CVD Growth and Optoelectronic Applications

et al. 2021

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“…The Sn fractions in the NiGeSn and GeSn layers are ∼10% (Figure d). The average composition of Ni is ∼50.2% in the NiGeSn layer, and it suggests that a Ni 1 (GeSn) 1 phase is formed. For NiGe alloys, the Ni 1 Ge 1 phase contributes a lower sheet resistance and SBH than other phases such as Ni 2 Ge 1 and Ni 5 Ge 3 .…”

Section: Results and Discussionmentioning

confidence: 99%

“…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%

“…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. 7−9 In those studies, the electron SBHs were obtained from the metal/n-GeSn contacts with low Sn fractions (0− 3.4%), 8 or they were indirectly extracted from the hole 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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“…For the Ge NW device, possible boron deactivation 26 in the top Ge for smaller NWs and less B segregation during NiGe formation 27 cause rapid contact resistance increase as the NW diameter decreases. For GeSn/Ge NW p-FETs, a higher density of boron segregated at the NiGeSn/GeSn interface 28 and the smaller SBH of NiGeSn/GeSn result in lower contact resistance increasing rate with decreasing NW diameter, compared to the Ge p-FET. Next, the influence of the NW diameter scaling on the electrical characteristics of GeSn/Ge and Ge pFETs is studied by analyzing the dependence of SS and drain-induced-barrier-lowering (DIBL) on the NW diameters.…”

Section: Electrical Characterizationmentioning

confidence: 99%

Epitaxial GeSn/Ge Vertical Nanowires for p-Type Field-Effect Transistors with Enhanced Performance

Liu

Yang

Shkurmanov

et al. 2020

ACS Appl. Nano Mater.

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Harvesting the full potential of single crystal semiconductor nanowires (NWs) for advanced nanoscale field-effect transistors (FETs) requires a smart combination of charge control architecture and functional semiconductors. In this article, high performance vertical gate-all-2 around nanowire p-type pFETs are presented. The device concept is based on advanced Ge0.92Sn0.08/Ge group IV epitaxial heterostructures, employing quasi-one-dimensional semiconductor nanowires fabricated with a top-down approach. The advantage of using a heterostructure is the possibility of electronic band engineering with band offsets tunable by changing the semiconductor stoichiometry and elastic strain. The use of a Ge0.92Sn0.08 layer as the source in GeSn/Ge NW pFETs results in a small subthreshold slope of 72 mV/dec and a high ION/IOFF ratio of 3×10 6 . A ~32% drive current enhancement is obtained compared to vertical Ge homojunction NW control devices. More interestingly, the drain-induced-barrier lowering is much smaller with GeSn instead of Ge as the source. The general improvement of the transistor's key figures of merits originates from the valence band offset at the Ge0.92Sn0.08/Ge heterojunction, as well as from a smaller NiGeSn/GeSn contact resistivity.

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Schottky barrier tuning via dopant segregation in NiGeSn-GeSn contacts

Cited by 21 publications

References 42 publications

Review of Si-Based GeSn CVD Growth and Optoelectronic Applications

Review of Si-Based GeSn CVD Growth and Optoelectronic Applications

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

Epitaxial GeSn/Ge Vertical Nanowires for p-Type Field-Effect Transistors with Enhanced Performance

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