Germanium strips for channeling: Study of the crystal quality after slicing and chemical etching

Aiming at the fabrication of germanium strips with lateral faces provided of excellent crystal quality for swift proton beams channeling, two different cutting techniques (diamond saw, DS, and wire electrical discharge machining, WEDM) were adopted to obtain germanium strips from Ga doped wafers (100 mm diameter, 500 \u3bcm thickness). After cutting, the damaged layer was removed by using two different chemical etching compositions, whose etch rate, anisotropy ratio and effects on morphology were investigated. The etch pits density of the as received material was evaluated through selective chemical etching and inspection with optical microscope, whereas the surface morphology of the as cut surface and after chemical treatment was investigated by scanning electron microscopy (SEM). The physical nature, amount and in-depth distribution of the cut induced lattice distortions were analyzed by low energy channeling Rutherford Backscattering Spectrometry (c-RBS), Raman spectroscopy and high resolution X-ray diffraction (HRXRD). The same set of techniques was also applied to monitor the structure evolution with increasing etching time. In the case of WEDM cut samples, though a remarkable recovery of the pristine crystal quality was achieved through removal of the sub-surface damage by prolonged wet etching as pointed out by c-RBS and HRXRD, the trend in crystal quality enhancement versus etching time is not as regular and reproducible as evidenced by the same techniques for DS samples