Solution-based coating and printing of polycrystalline Ge films using GeO₂ solution by moderate-pressure hydrogen plasma reduction

Abstract

A printable-formation method for Ge films using a GeO 2 solution was developed in this study. The GeO 2 film was prepared by applying GeO 2 ink on a glass substrate and reducing it using high-pressure H 2 -based plasma. The crystallinity, electrical conductivity, and photosensitivity of the films were examined before and after the plasma treatment. The film transformed from amorphous GeO 2 to crystalline Ge after treatment with the H 2 -based plasma. The Ge film obtained after H 2 plasma reduction exhibited an electrical resistivity of 4000 Ω cm and a photosensitivity of 1.9 under AM 1.5G illumination of 100 mW cm −2 . In addition, the dependence of the reduction behavior of the GeO 2 film on the process parameters, such as the input power, substrate temperature, treatment time, and hydrogen concentration, were investigated systematically. The reduction of GeO 2 by H 2 plasma proceeded with an increase in the input power. The thickness of the reduced Ge film depended strongly on the substrate temperature, and the plasma reduction process required a low reduction temperature and short reaction time as compared to those of the thermal reduction process. The presence of only 4% H 2 gas in the process atmosphere played an important role in the reduction and crystallization of the Ge film, although pure He plasma could also reduce the GeO 2 film. Thus, we demonstrated the position-controlled preparation of Ge films using a commercial inkjet printer loaded with a GeO 2 ink solution.