Abstract
Low temperature (<200 oC) crystallization of GeSn (substitutional Sn concentration: >8%) on insulating substrates is essential to realize next generation flexible electronics. To achieve this, a growth method of high quality GeSn films on insulating substrates by combination of laser irradiation and subsequent thermal annealing is developed. Here, the laser fluence is chosen as weak, which is below the critical fluence for crystallization of GeSn. It is clarified that for samples irradiated with weak laser fluence, complete crystallization of GeSn films is achieved by subsequent thermal annealing at ∼170 oC without incubation time. In addition, the quality of GeSn films obtained by this method is higher compared with conventional growth techniques such as melting growth by pulsed laser annealing or solid-phase crystallization (SPC) without pre-laser irradiation. Substitutional Sn concentrations in the grown layers estimated by Raman spectroscopy measurements are 8-10%, which far exceed thermal equilibrium solid-solubility of Sn in Ge (∼2%). These phenomena are explained by generation of a limited number of nuclei by weak laser irradiation and lateral SPC by subsequent thermal annealing. This method will facilitate realization of next-generation high performance devices on flexible insulating substrates.
Highlights
Low-temperature (
GeSn crystals on insulator structures are strongly desired to realize high-speed thin film transistors (TFTs) and high-efficiency optical devices for generation electronics. This is because GeSn crystals have higher carrier mobility than Si and Ge due to the direct-transition energy band structure with smaller effective mass of carriers for high substitutional Sn concentrations (>8%).[1,2]
We reported solid phase crystallization (SPC) of amorphous GeSn (a-GeSn) films with initial Sn concentration of 20% at a low temperature (
Summary
Low-temperature (
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