Role of an interlayer at a TiN/Ge contact to alleviate the intrinsic Fermi-level pinning position toward the conduction band edge

Yamamoto, Keisuke; Mitsuhara, Masatoshi; Hiidome, Keisuke; Noguchi, R.; Nishida, Minoru; Wang, Dong; Nakashima, Hiroshi

doi:10.1063/1.4870510

Cited by 31 publications

(33 citation statements)

References 18 publications

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“…The Richardson constant of Ge is 143 A cm –2 K 2 , and the contact area is 100 × 100 μm 2 . Therefore, the SBH between GeSn and TiN was derived to be 0.49 eV, which agrees well with other reported values. , Figure b shows the band diagram of the TiN/GeSn heterojunction. The electron affinity and bandgap of GeSn with 8% Sn composition obtained from the literature are 4.0 and 0.60 eV, respectively .…”

Section: Resultssupporting

confidence: 90%

Flexible Titanium Nitride/Germanium-Tin Photodetectors Based on Sub-Bandgap Absorption

Liao

Kim

2021

ACS Appl. Mater. Interfaces

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We report an enhanced performance of flexible titanium nitride/germanium-tin (TiN/GeSn) photodetectors (PDs) with an extended photodetection range based on sub-bandgap absorption. Single-crystalline GeSn membranes transfer-printed on poly(ethylene terephthalate) are integrated with plasmonic TiN to form a TiN/GeSn heterojunction. Formation of the heterojunction creates a Schottky contact between the TiN and GeSn. A Schottky barrier height of 0.49 eV extends the photodetection wavelength to 2530 nm and further enhances the light absorption capability within the detection range. In addition, finite-difference time-domain simulation proves that the integration of TiN and GeSn could enhance average absorption from 0.13 to 0.33 in the near-infrared (NIR) region (e.g., 1400–2000 nm) and more than 70% of light is absorbed in TiN. The responsivity of the fabricated TiN/GeSn PDs is increased from 30 to 148.5 mA W–1 at 1550 nm. There is also an ∼180 nm extension in the optical absorption wavelength of the flexible TiN/GeSn PD. The enhanced performance of the device is attributed to the absorption and separation of plasmonic hot carriers via TiN and the TiN/GeSn junction, respectively. The effect of external uniaxial strain is also investigated. A tensile strain of 0.3% could further increase the responsivity from 148.5 to 218 mA W–1, while it is decreased to 102 mA W–1 by 0.25% compressive strain. In addition, the devices maintain stable performance after multiple and long bending cycles. Our results provide a robust and cost-effective method to extend the NIR photodetection capability of flexible group IV PDs.

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Section: Resultssupporting

confidence: 90%

Flexible Titanium Nitride/Germanium-Tin Photodetectors Based on Sub-Bandgap Absorption

Liao

Kim

2021

ACS Appl. Mater. Interfaces

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“…32 The effect of Ge−N bonds to reduce the electron SBH of the metal/n-Ge contact has been also studied with a TiN/n-Ge structure. 1,33 The Ge−N bonds form an interface dipole at the metal nitride/Ge interface, and the dipole can reduce the SBH of the contact. 32 The presence of Ge−N bonds was verified using an X-ray photoelectron spectroscopy (XPS) analysis on the TaN/n-Ge structure as shown in Figure 7a, where the binding energy of the Ge−N bond is located at 397.6 eV in the N 1s spectra.…”

Section: Resultsmentioning

confidence: 99%

“…An ultralow source/drain (S/D) contact resistance should be achieved to utilize the advantages of Ge in nanoscale metal−oxide−semiconductor field-effect transistors (MOS-FETs). 1 However, it is difficult to obtain an ultralow contact resistance in n-type Ge (n-Ge) due to the low solubility and high diffusivity of n-type dopants 2 and the large electron Schottky barrier height (SBH) induced by severe Fermi-level pinning (FLP) at the metal/Ge interface. When the metal is in contact with Ge, the Fermi level on the metal side is strongly pinned near the edge of the valence band of Ge, resulting in an SBH of approximately 0.55 eV regardless of the value of the metal work-function, as shown in Figure 1a.…”

Section: Introductionmentioning

confidence: 99%

“…Germanium (Ge) has emerged as a sound substitute for silicon (Si) in the next-generation complementary metal–oxide–semiconductor (CMOS) technology, due to its higher carrier mobility. An ultralow source/drain (S/D) contact resistance should be achieved to utilize the advantages of Ge in nanoscale metal–oxide–semiconductor field-effect transistors (MOSFETs) . However, it is difficult to obtain an ultralow contact resistance in n-type Ge (n-Ge) due to the low solubility and high diffusivity of n-type dopants and the large electron Schottky barrier height (SBH) induced by severe Fermi-level pinning (FLP) at the metal/Ge interface.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Fermi-Level Unpinning Technique with Excellent Thermal Stability for n-Type Germanium

Kim¹,

Kim²,

Lee

et al. 2017

ACS Appl. Mater. Interfaces

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A metal-interlayer-semiconductor (M-I-S) structure with excellent thermal stability and electrical performance for a nonalloyed contact scheme is developed, and considerations for designing thermally stable M-I-S structure are demonstrated on the basis of n-type germanium (Ge). A thermal annealing process makes M-I-S structures lose their Fermi-level unpinning and electron Schottky barrier height reduction effect in two mechanisms: (1) oxygen (O) diffusion from the interlayer to the contact metal due to high reactivity of a pure metal contact with O and (2) interdiffusion between the contact metal and semiconductor through grain boundaries of the interlayer. A pure metal contact such as titanium (Ti) provides very poor thermal stability due to its high reactivity with O. A structure with a tantalum nitride (TaN) metal contact and a titanium dioxide (TiO) interlayer exhibits moderate thermal stability up to 400 °C because TaN has much lower reactivity with O than with Ti. However, the TiO interlayer cannot prevent the interdiffusion process because it is easily crystallized during thermal annealing and its grain boundaries act as diffusion path. A zinc oxide (ZnO) interlayer doped with group-III elements, such as an aluminum-doped ZnO (AZO) interlayer, acts as a good diffusion barrier due to its high crystallization temperature. A TaN/AZO/n-Ge structure provides excellent thermal stability above 500 °C as it can prevent both O diffusion and interdiffusion processes; hence, it exhibits Ohmic contact properties for all thermal annealing temperatures. This work shows that, to fabricate a thermally stable and low resistive M-I-S contact structure, the metal contact should have low reactivity with O and a low work-function, and the interlayer should have a high crystallization temperature and a low conduction band offset to Ge. Furthermore, new insights are provided for designing thermally stable M-I-S contact schemes for any semiconductor material that suffers from the Fermi-level pinning problem.

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“…To address this issue, several attempts have recently been made to achieve ohmic contact even for an n-Ge contact by direct deposition of metal nitride such as TaN [6], TiN [7] and WN x [8]. These results demonstrate that nitrogen-associated defects and/or interfacial layers between metal and Ge play a crucial factor to modulate the SBH.…”

Section: Introductionmentioning

confidence: 99%

The Mechanism of Schottky Barrier Modulation of Tantalum Nitride/Ge Contacts

Seo

Lee

Baek

et al. 2015

IEEE Electron Device Lett.

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In this letter, we discuss the mechanism of Schottky barrier height (SBH) modulation of the TaN/Ge contact by varying the nitrogen concentration in the TaN. The Fermi level, which is strongly pinned near the valence band edge of Ge, moves to the conduction band edge of Ge with higher nitrogen concentration in the reactive sputtered TaN. This SBH modulation is attributed to the presence of an electric dipole induced by Ge-N bonds at the interface of the TaN/Ge contact. This SBH modulation due to the semiconductor-nitrogen bonds at the interface is not specific to TaN/Ge, but rather is a general feature in various transitionmetal nitride systems on various semiconductors.Index Terms-Germanium, Fermi level de-pinning, tantalum nitride, Schottky barrier height.

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Role of an interlayer at a TiN/Ge contact to alleviate the intrinsic Fermi-level pinning position toward the conduction band edge

Cited by 31 publications

References 18 publications

Flexible Titanium Nitride/Germanium-Tin Photodetectors Based on Sub-Bandgap Absorption

Flexible Titanium Nitride/Germanium-Tin Photodetectors Based on Sub-Bandgap Absorption

Fermi-Level Unpinning Technique with Excellent Thermal Stability for n-Type Germanium

The Mechanism of Schottky Barrier Modulation of Tantalum Nitride/Ge Contacts

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