High hole mobility (≥500 cm 2 V −1 s −1 ) polycrystalline Ge films on GeO 2 -coated glass and plastic substrates

Applied Physics Letters

et al. 2019

Low-temperature synthesis of polycrystalline (poly-) Ge on insulators is a key technology to integrate Ge-CMOS into existing devices. However, Fermi level control in poly-Ge has been difficult because poly-Ge has remained naturally highly p-type due to its defect-induced acceptors. We investigated the formation of n-type poly-Ge (thickness: 100-500 nm) using the advanced solid-phase crystallization technique with Sb-doped densified precursors. Sb doping on the order of 10 20 cm À3 facilitated lateral growth rather than nucleation in Ge, resulting in large grains exceeding 15 lm at a low growth temperature (375 C). The subsequent heat treatment (500 C) provided the highest electron mobility (200 cm 2 /V s) and the lowest electron density (5 Â 10 17 cm À3) among n-type poly-Ge directly grown on insulators. These findings will provide a means for the monolithic integration of high-performance Ge-CMOS into Si-LSIs and flat-panel displays.

mentioning

confidence: 99%

Sb-doped crystallization of densified precursor for n-type polycrystalline Ge on an insulator with high carrier mobility

Takahara

Moto

Applied Physics Letters

et al. 2019

“…42 We further updated the Hall hole mobility to 620 cm 2 /V s by thickening Ge, postannealing at 500 °C, and inserting a GeO 2 underlayer. 43,44 This hole mobility is the highest ever recorded for a semiconductor film directly grown on an insulator at temperatures below 900 °C.…”

Section: Introductionmentioning

confidence: 84%

Influence of grain boundaries on the properties of polycrystalline germanium

Journal of Applied Physics

Suemasu

Toko

2020

Self Cite

High-speed thin film transistors based on plastic substrates are indispensable to realize next-generation flexible devices. Here, we synthesized a polycrystalline Ge layer, which had the highest quality ever, on GeO 2 -coated substrates using advanced solid-phase crystallization at 375 °C. X-ray diffraction and Raman spectroscopy revealed that Ge on plastic had a compressive strain, while conventional Ge with a glass substrate had a tensile strain. This behavior was explained quantitatively from the difference in the thermal expansion coefficients between Ge and the substrate. Electron backscatter diffraction analyses showed that the Ge had large grains up to 10 μm, while many intragranular grain boundaries were present. The potential barrier height of the grain boundary was lower for the plastic sample than that for the glass sample, which was discussed in terms of the strain direction. These features resulted in a hole mobility (500 cm 2 /V s) exceeding that of a single-crystal Si wafer. The findings and knowledge will contribute to the development of polycrystalline engineering and lead to advanced flexible electronics.

“…29 Additionally, l Hall was updated to 620 cm 2 /Vs by thickening a-Ge, postannealing at 500 C, and inserting GeO 2 underlayer. 30,31 This l Hall is the highest ever recorded for a thin film directly grown on an insulator at temperatures below 900 C. In the present study, we fabricate poly-Ge TFTs using SPC-Ge and discuss the relationship between the film properties (thickness, l Hall , and p) and TFT characteristics (field-effect mobility: l FE and on/off currents). We demonstrate the highest l FE among low-temperature (<500 C) poly-Ge TFTs without minimizing the channel region.…”

mentioning

confidence: 92%

Polycrystalline thin-film transistors fabricated on high-mobility solid-phase-crystallized Ge on glass

Moto

Yamamoto

Applied Physics Letters

et al. 2019