Influence of germanium incorporation on the structural and electrical properties of boron-doped ultrathin poly-Si_1-x Ge _x films deposited by chemical vapour deposition

A few properties of polycrystalline silicon germanium (poly-Si _1-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-Si _1-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.