High carrier mobility of Sn-doped polycrystalline-Ge films on insulators by thickness-dependent low-temperature solid-phase crystallization

Taizoh Sadoh, Yuki Kai, Ryo Matsumura, Kenta Moto, Masanobu Miyao

Research output: Contribution to journalArticle

19 Citations (Scopus)

Abstract

To realize the advanced thin-film transistors (TFTs), high-carrier-mobility semiconductor films on insulator structures should be fabricated with low-temperature processing conditions (≤500 °C). To achieve this, we investigated the solid-phase crystallization of amorphous-GeSn films on insulating substrates under a wide range of Sn concentrations (0%-20%), film thicknesses (30-500 nm), and annealing temperatures (380-500 °C). Our results reveal that a Sn concentration close to the solid solubility of Sn in Ge (∼2%) is effective in increasing the grain-size of poly-GeSn. In addition, we discovered that the carrier mobility depends on the film thickness, where the mobilities are determined by the counterbalance between two different carrier scattering mechanisms. Here, vacancy-related defects dominate the carrier scattering near the insulating substrates (≤∼120 nm), and grain-size determined by bulk nucleation dominates the grain-boundary scattering of thick films (≥∼200 nm). Consequently, we obtained the maximum mobilities in samples with a Sn concentration of 2% and a film thickness of 200 nm. The effect of increasing the grain-size of poly-GeSn by lowering the annealing temperature was also clarified. By combining these results, a very high carrier mobility of 320 cm2/Vs was obtained at a low temperature of 380 °C. This mobility is about 2.5 times as high as previously reported data for Ge and GeSn films grown at low temperatures (≤500 °C). Our technique therefore opens up the possibility of high-speed TFTs for use in the next generation of electronics.

Original languageEnglish
Article number232106
JournalApplied Physics Letters
Volume109
Issue number23
DOIs
Publication statusPublished - Dec 5 2016

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carrier mobility
solid phases
film thickness
grain size
insulators
crystallization
transistors
scattering
counterbalances
annealing
thin films
thick films
solubility
grain boundaries
high speed
nucleation
temperature
defects
electronics

All Science Journal Classification (ASJC) codes

  • Physics and Astronomy (miscellaneous)

Cite this

High carrier mobility of Sn-doped polycrystalline-Ge films on insulators by thickness-dependent low-temperature solid-phase crystallization. / Sadoh, Taizoh; Kai, Yuki; Matsumura, Ryo; Moto, Kenta; Miyao, Masanobu.

In: Applied Physics Letters, Vol. 109, No. 23, 232106, 05.12.2016.

Research output: Contribution to journalArticle

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