Recrystallization of Ge thin film on SiO₂ substrates using a two-step annealing process

The fabrication of high-quality crystalline germanium thin films (GeTF) on an amorphous SiO₂ layer is crucial for the realization of high performance-, low cost III-V solar cells used in many applications. Herein, we report the growth of a high-quality crystalline GeTF on SiO₂/Si substrates using an ultra-vacuum chemical vapor deposition (UHV-CVD) method. GeTF was grown on the SiO₂ layer using a two-step growth and multi-annealing processes. The fabrication method involved the deposition of a 1^st seeding layer, annealing, and deposition of a 2^nd main layer followed by three times of cyclic annealing. The crystallization of the seeding layer having a thickness of less than 10 nm could be ascribed to the evolution of polycrystalline structures in the main layer. The cyclic annealing performed after the deposition of the main layer is also found to be crucial for the formation of single crystalline, high-quality Ge films on SiO₂ substrates with <311> direction. The cyclic annealing results in a further reduction of the defects, thereby threading dislocations significantly to a density of ~ 5.311 × 10⁷ cm⁻². Electrical measurements using the van der Pauw method revealed that the GeTF exhibits p-type characteristics and a high mobility of 360.10 cm²/Vs at room temperature. [Figure not available: see fulltext.]