Abstract
High-carrier mobility semiconductors on insulators are essential for fabricating advanced thin-film transistors, allowing for three-dimensional integrated circuits or high-performance mobile terminals. We investigate the low-temperature (375–450 °C) solid-phase crystallization (SPC) of Ge on a glass substrate, focusing on the precursor conditions. The substrate temperature during the precursor deposition, Td, ranged from 50 to 200 °C. According to the atomic density of the precursor and the Td dependent SPC properties, the precursor conditions were determined by three regimes: the low-density regime (Td < 100 °C), high-density regime (100 ≤ Td ≤ 125 °C), and nucleation regime (Td > 125 °C). The use of the precursor in the narrow high-density regime enabled us to form SPC-Ge with a hole mobility of 340 cm2/Vs, the highest value among semiconductor thin films grown on insulators at low temperature (<900 °C). The origins of the high hole mobility were determined to be both a large grain size (5 µm) and a low energy barrier height (6.4 meV) for the grain boundary. The findings from and knowledge gained in this study, that is, the influence of the precursor conditions on subsequent crystal growth, will be universal and applicable to various materials.
Highlights
Germanium has been proposed as a major candidate for next-generation electronic devices because of its high carrier mobility and good compatibility with Si1–3
Achieve pure Polycrystalline Ge (poly-Ge) with a hole mobility of 340 cm2/Vs by controlling the atomic density of an a-Ge precursor. This hole mobility is the highest ever recorded for a semiconductor thin film including Ge, Si, compound, oxide, and organic materials formed on insulators at temperatures below 900 °C
The crystal quality and electrical properties of the poly-Ge layer formed by solid-phase crystallization (SPC) varied with the deposition temperature, Td, of the precursor Ge layer
Summary
Germanium has been proposed as a major candidate for next-generation electronic devices because of its high carrier mobility and good compatibility with Si1–3. Polycrystalline Ge (poly-Ge) thin films have been directly formed on glass or plastic substrates at low temperatures using solid-phase crystallization (SPC)[17,18,19,20,21], laser annealing[22,23,24], chemical vapor deposition (CVD)[25,26], flash lamp annealing (FLA)[27], and metal-induced crystallization (MIC)[28,29,30,31,32]. This hole mobility is the highest ever recorded for a semiconductor thin film including Ge, Si, compound, oxide, and organic materials formed on insulators at temperatures below 900 °C
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