Enhanced mobility of Sn-doped Ge thin-films (≤50nm) on insulator for fully depleted transistors by nucleation-controlled solid-phase crystallization

Chang Xu, Xiangsheng Gong, Masanobu Miyao, Taizoh Sadoh

Research output: Contribution to journalArticle

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Abstract

High-speed fully depleted thin-film transistors (TFTs) for low-power consumption are required for next-generation electronics, such as three-dimensional large-scale integrated circuits and advanced system-in-displays. For this purpose, high-carrier-mobility semiconductor thin-films (thickness: ≤∼50 nm) on insulator structures should be fabricated under low-temperature processing conditions (≤500 °C). To achieve this, solid-phase crystallization of amorphous GeSn (a-GeSn) with low Sn concentration (2%) is investigated for a wide range of film thicknesses (30 - 200 nm), where thin a-Si underlayers (thickness: 0 - 20 nm) are introduced between a-GeSn films and substrates. GeSn is polycrystallized by annealing at 450 °C, keeping Si underlayers amorphous. Crystal grains of almost identical sizes are obtained for GeSn thicknesses of 30 - 50 nm, though grain sizes significantly decrease for thicknesses exceeding 50 nm owing to enhanced bulk nucleation. A detailed analysis of GeSn films (thickness: 50 nm) reveals that grain sizes are decreased by introducing a-Si underlayers (thickness: 3 - 20 nm), e.g., from ∼10 μm to 2 - 3 μm. This phenomenon is attributed to the change in dominant nucleation sites from the interface to the bulk, which significantly decreases grain-boundary scattering of carriers through a decrease in the barrier heights at grain boundaries. As a result, a high carrier mobility of 200 - 300 cm2/V s is realized for GeSn thin-films (thickness: 30 - 50 nm) grown with a-Si underlayers. The mobility (200 - 300 cm2/V s) is the largest ever reported data for Ge and GeSn thin-films (thickness: 30 - 50 nm) grown at low temperatures (≤500 °C). This technique will facilitate the realization of high-speed fully depleted TFTs for next-generation electronics.

Original languageEnglish
Article number042101
JournalApplied Physics Letters
Volume115
Issue number4
DOIs
Publication statusPublished - Jul 22 2019

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solid phases
film thickness
transistors
insulators
nucleation
crystallization
thin films
carrier mobility
grain boundaries
grain size
high speed
electronics
integrated circuits
low concentrations
annealing
scattering
crystals

All Science Journal Classification (ASJC) codes

  • Physics and Astronomy (miscellaneous)

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Enhanced mobility of Sn-doped Ge thin-films (≤50nm) on insulator for fully depleted transistors by nucleation-controlled solid-phase crystallization. / Xu, Chang; Gong, Xiangsheng; Miyao, Masanobu; Sadoh, Taizoh.

In: Applied Physics Letters, Vol. 115, No. 4, 042101, 22.07.2019.

Research output: Contribution to journalArticle

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abstract = "High-speed fully depleted thin-film transistors (TFTs) for low-power consumption are required for next-generation electronics, such as three-dimensional large-scale integrated circuits and advanced system-in-displays. For this purpose, high-carrier-mobility semiconductor thin-films (thickness: ≤∼50 nm) on insulator structures should be fabricated under low-temperature processing conditions (≤500 °C). To achieve this, solid-phase crystallization of amorphous GeSn (a-GeSn) with low Sn concentration (2{\%}) is investigated for a wide range of film thicknesses (30 - 200 nm), where thin a-Si underlayers (thickness: 0 - 20 nm) are introduced between a-GeSn films and substrates. GeSn is polycrystallized by annealing at 450 °C, keeping Si underlayers amorphous. Crystal grains of almost identical sizes are obtained for GeSn thicknesses of 30 - 50 nm, though grain sizes significantly decrease for thicknesses exceeding 50 nm owing to enhanced bulk nucleation. A detailed analysis of GeSn films (thickness: 50 nm) reveals that grain sizes are decreased by introducing a-Si underlayers (thickness: 3 - 20 nm), e.g., from ∼10 μm to 2 - 3 μm. This phenomenon is attributed to the change in dominant nucleation sites from the interface to the bulk, which significantly decreases grain-boundary scattering of carriers through a decrease in the barrier heights at grain boundaries. As a result, a high carrier mobility of 200 - 300 cm2/V s is realized for GeSn thin-films (thickness: 30 - 50 nm) grown with a-Si underlayers. The mobility (200 - 300 cm2/V s) is the largest ever reported data for Ge and GeSn thin-films (thickness: 30 - 50 nm) grown at low temperatures (≤500 °C). This technique will facilitate the realization of high-speed fully depleted TFTs for next-generation electronics.",
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