Classification of different post-hyperdoping treatments for enhanced crystallinity of IR-sensitive femtosecond-laser processed silicon

Abstract

Crystalline silicon becomes photosensitive and absorbing in the sub-bandgap spectral region if hyperdoped, i.e. supersaturated to a level above the solubility limit in thermal equilibrium, by deep impurities, such as sulfur. Here we apply femtosecond laserpulses to crystalline silicon in a SF6 atmosphere as hyperdoping method. The ultrashort laser pulses cause crystal damage and amorphous phases that would decrease quantum efficiency in a potential optoelectronic device application. We investigate five different post-hyperdoping methods: three etching techniques (ion beam etching IBE, reactive ion etching RIE, and wet-chemical etching HNA) as well as ns-annealing and minute-long thermal annealing and study their impact on crystallinity by Raman spectroscopy and absorptance in the visible and near infrared wavelength regime. We use femtosecond laser hyperdoped silicon (fs-hSi) with two different levels of surface roughness to study a potential dependence on the impact of post-treatments. In our investigation, ns-annealing leads to the best results, characterized by a high Raman crystallinity and a high remaining absorptance in the sub-bandgap spectral region of silicon. Within the used etching methods IBE outperforms the other etching methods above a certain level of fs-hSi surface roughness. We relate this to the specific anisotropic material removal behavior of the IBE technique and back this up with simulations of the effect of the various etching processes.

The Mechanism Behind the Annealing‐Induced Reduction of Infrared Absorption in Zinc‐Hyperdoped Silicon

“…[14,15] Therefore, it is crucial to control and recover the lattice defects introduced during femtosecond laser processing to minimize their impacts on the electrical properties of optoelectronic devices, by means of thermal annealing, chemical treatments, or epitaxial growth of materials. [16] Annealing is the most commonly used technique to mitigate the defects induced by femtosecond laser processing. By subjecting the processed material to an appropriate annealing process, the recrystallization of the semiconductor material can be promoted, leading to the reduction or even elimination of defects and stresses in it.…”