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

Abstract

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 1st seeding layer, annealing, and deposition of a 2nd 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 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.