Electrical properties of pseudo-single-crystalline germanium thin-film-transistors fabricated on glass substrates

Abstract

By developing a low-temperature (≤300 °C) fabrication process for the gate-stack structure on Ge(111), we study electrical properties of thin film transistors (TFTs) consisting of (111)-oriented pseudo-single-crystalline-germanium (PSC-Ge) channels on glass. Although the Hall mobility (μHall) of p-type PSC-Ge layers reaches 210 cm2/V s and the gate-stack/Ge interface has low trap density, we observe field-effect-mobility (μFE) fluctuation in the p-channel TFTs from 8.2 to 71 cm2/V s, depending on the thickness of the PSC-Ge layer. Considering the μFE fluctuation and low Ion/Ioff ratio in the p-TFTs, we infer the presence of defective Ge layers near the surface of the glass substrate. This study reveals that it is quite important for the high-performance p-Ge TFTs to improve the quality of the Ge layer near the surface of the glass substrate or to choose other materials with better Ge/substrate interface qualities.

High-hole mobility polycrystalline Ge on an insulator formed by controlling precursor atomic density for solid-phase crystallization

“…The electrical properties of the resulting poly-Ge layers were evaluated by Hall effect measurements. All samples showed p-type conduction, similar to conventional non-doped poly-Ge 17 , 25 , 27 , 32 . This is because dangling bonds in Ge provide shallow acceptor levels and then generate holes at room temperature 39 .…”

“…To avoid thermal damage to the substrates and to lower the process costs, the low-temperature formation (<600 °C) of GOI is necessary. Polycrystalline Ge (poly-Ge) thin films have been directly formed on glass or plastic substrates at low temperatures using solid-phase crystallization (SPC) 17 – 21 , laser annealing 22 – 24 , chemical vapor deposition (CVD) 25 , 26 , flash lamp annealing (FLA) 27 , and metal-induced crystallization (MIC) 28 – 32 . The use of these techniques has allowed researchers to fabricate Ge thin-film transistors (TFTs) via all-low-temperature processes 20 , 21 , 27 , 32 .…”

“…In 2009, we demonstrated a hole mobility of 140 cm 2 /Vs for poly-Ge on glass formed by two-step SPC of amorphous (a−) Ge at 425 °C followed by 500 °C 17 . In the last couple of years, the highest hole mobility has been updated frequently: FLA has achieved 200 cm 2 /Vs 27 , followed by Au-induced crystallization achieving 160–210 cm 2 /Vs 31 , 32 . On the other hand, incorporating Sn in Ge has been found to be effective for enhancing the hole mobility 33 – 35 .…”

Effects of Al grain size on metal-induced layer exchange growth of amorphous Ge thin film on glass substrate

“…Highly (111)-oriented Ge layers have been recently achieved on glass [18][19][20][21][22][23][24] and plastic substrates [25][26][27] owing to the development of metal-induced layer exchange (MILE), that is, crystallization via the layer exchange between a-Ge and metals. The MILE is a powerful technique to fabricate high-speed thin-film transistors [28] or vertically aligned nanowires [29,30] on amorphous substrates including plastics.…”

Effect of interlayer on silver-induced layer exchange crystallization of amorphous germanium thin film on insulator

“…On the other hand, in a Au-Ge system, the resulting Ge layer shows relatively good electrical properties (p = 2 × 10 17 cm -3 and hole mobility: 25) This has allowed for the formation of a thin-film transistor by an all-lowtemperature process. 30) However, Au has difficulty in being used for large-area devices because it is expensive and unstable.…”