Effect of Nanosecond Ultraviolet Laser Pulses on the Surface of Germanium Single Crystals

For the first time, a detailed comprehensive study is conducted of the dry etching of dislocation and dislocation-free samples of germanium on planes {111}, {110}, and {100}. Etching is performed by exposure to pulses of nanosecond ultraviolet (UV) laser radiation of the subthreshold intensity (wavelength, 355 nm; duration, ~10 ns; energy density, ~0.5–1.3 J/cm2; pulse repetition rate, 100 Hz; and divergence, 1–2 mrad). Before and after the laser heat treatment of the surface, the samples are examined using a Zygo optical profilometer and a scanning electron microscope. Features of the nature of the damage to the surfaces corresponding to different crystallographic planes of single crystals of industrial dislocation germanium are revealed. They are compared with the data on the subthreshold damage of typical dislocation-free crystals. It is shown that in dislocation samples of germanium on the {111} plane, it is possible to create a regime of exposure to radiation, leading to the formation of etch pits, which is outwardly identical to the dislocation pits detected during selective chemical etching. Their concentration corresponds in order of magnitude to the density of dislocations. On the {100} plane of dislocation samples, etching results are also found, which clearly have a crystallographic nature. At the energy density of the acting radiation ≥0.4 J/cm2 on the surfaces of dislocation (plane {100}) and dislocation-free germanium (planes {111}, {100}, {110}), only individual spots of ~50 µm and individual microcraters of ~0.1–1 µm having crystallographic features are recorded. The possibility of the environmentally friendly detection of dislocations in germanium without the use of chemical reagents is shown.