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

Toko, Kaoru  ,  Yoshimine, Ryota  ,  Moto, Kenta  ,  Suemasu, Takashi

7p.16981 , 2017-12 , Nature Publishing Group
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.

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