Modification of a Germanium Surface Exposed to Radiation of a Nanosecond Ultraviolet Laser

• Published in: Russian microelectronics 2021-12, Vol.50 (8), p.649-656
• Main Authors: Zheleznov, V. Yu, Malinsky, T. V., Mikolutsky, S. I., Rogalin, V. E., Filin, S. A., Khomich, Yu. V., Yamshchikov, V. A., Kaplunov, I. A., Ivanova, A. I.
• Format: Article
• Language: English
• Subjects: Ablation; Chemical etching; Crystal dislocations; Crystal growth; Crystal surfaces; Electrical Engineering; Engineering; Etching; Flux density; Germanium; Lasers; Neodymium lasers; Nucleation; Pits; Pyramids; Radiation; Radiation damage; Radiation effects; Single crystals; Surface layers; Ultraviolet lasers; Ultraviolet radiation
• ISSN: 1063-7397; 1608-3415
• DOI: 10.1134/S1063739721080102

The modification of the polished {111} surface of single-crystal germanium ( n -type of conductivity, resistivity 47 Ohm cm) as a result of exposure to focused frequency-pulse radiation of nanosecond ultraviolet Nd : YaG laser are studied by optical profilometry, as well as scanning electron and probe microscopy. It is revealed that the threshold of the plasma formation with the formation of a crater on the surface arises at the energy density of laser radiation E ~ 1.2–1.3 J/cm 2 . When the sample is stationary at E ~ 0.1 J/cm 2 irreversible damage to the surface occurred. When scanning a surface with radiation at E ~ 0.50–1.15 J/cm 2 , in the absence of noticeable traces of crater formation, the formation of etching pits is observed with a regular triangular shape, the concentration of which is (3–5) × 10 5 cm –2 . The shapes resemble dislocation etching pits obtained by selective chemical etching. Dislocations are detected by ablation as a result of exposure to laser radiation. The centers of ablation nucleation are dislocations emerging on the crystal surface. The transverse size of the etching pits is ~5–10 μm, and their overlap results in an alternating pattern of trihedral pyramids formed by the {111} planes. The rounded edges and tops of the pyramids are observed and the height of the profile of the figures is ~1–2 microns. The linear dimensions of the pits indicate a rapid course of the process. The rate of the formation of flat faces in the pits, which is ~0.1–0.3 m s –1 , which is several orders of magnitude higher than the rate of formation of the same faces during the crystal growth is set based on the total time of exposure to radiation on the surface of ∼200 ns. The depth of the surface layer in which the structure was formed is ∼15 μm.