Influence of germanium incorporation on the structural and electrical properties of boron-doped ultrathin poly-Si1−x Ge x films deposited by chemical vapour deposition

Abstract

A few properties of polycrystalline silicon germanium (poly-Si1−x Ge x ) films can be tailored by modulating the germanium incorporation. In this paper, the structural, mechanical and electrical properties of heavily doped ultrathin (~100 nm) poly-Si1−x Ge x films (0.84 ≤ x ≤ 0.88) fabricated by low-pressure chemical vapour deposition were investigated. For a boron concentration of ~2.2 × 1021 atoms/cm3, a slight increase of germanium fraction significantly enhances the deposition rate, crystallinity and Hall mobility while having negligible influence on the Young’s modulus and hardness. The grain size increases from ~6 to ~12 nm while the grain structure becomes more columnar. In addition, the resistivity decreases from 7.4 to 1.1 m Ω cm with a corresponding increase in the Hall mobility from ~0.9 to ~4.2 cm2 V−1 s−1. However, the Young’s modulus (~101 GPa) and hardness (~8.8 GPa) are virtually unaffected within the range of germanium fraction explored. In practice, poly-SiGe layer having low resistivity, high modulus, high mobility and low surface roughness can be successfully applied for resonators, biosensors and nanoswitches among others.