Structure changes in silicon irradiated by high energy ions of hydrogen, deuterium and helium

Abstract

Structural and optical properties of silicon irradiated by ions of 6.8 МеV hydrogen (p+ or H+), 13.6 МеV deuterium (heavy hydrogen 2H+ or D+) and 27.2 MeV helium (α-particles or He2+) with fluences Ф ≥ 5 ∙ 1016 сm–2 were studied using the complex of methods: selective etching and metallographic, ellipsometry and profilometry. The irradiated crystals were cut along the direction of irradiation, allowing to study the properties of silicon in the region of the ions’ path, braking and behind it. The projection lengths of the path of the ions of a given energy are about 360 microns for p+ and He2+ and about 780 m for D+. The main structural defects are observed in the braking region, where concentration of radiation defects is the largest. The widths of etched lines along ion stopping change in the direction from the sample edge (where temperature was lower due to the sample cooling during irradiation) to the center of irradiation and depend of the ion type. After proton irradiation silicon structure in the path region does not sufficiently change. Structure of the path region of helium irradiated Si changes essentially from the crystal form to the highly destroyed (perhaps, polycrystalline). At currents about 0.25 - 0.45 А and fluences Ф ≥ 1016 сm–2 the defect “walls” parallel to the stopping line appeared both in the path region, and behind stopping line at the distance equal to double projection length of the path. The number of the “walls” depended on the ion beam intensity. We consider that the soliton mechanism is responsible for the ordered structure creation in the region behind the stopping line. Periodic structures in the path region might appear due to the moving of the recrystallization front of the highly disordered layers, possible, amorphous, in the process of the highly energetic long-lasting ion irradiation.