Detection Characteristics of Ge detectors with microstructured amorphous Ge contacts

The established technique for producing position-sensitive structures by means of photolithography and subsequent plasma etching of grooves through detector contacts was applied for amorphous germanium contacts (a-Ge contacts). A simple 50-strip structure with a pitch of 615 μm was produced. Charge sharing between two adjacent strips (33 mm length) was investigated with the aid of 60-keV photons and 5.8-MeV α-particles. No charge losses were detected when irradiating the structured a-Ge contact of the 16-mm-thick detector with 60-keV photons. The same was concluded for α-particles hitting the unstructured p⁺-contact made by boron implantation. Moreover, excellent position information for α-particles, with an accuracy of about 30 μm, could be extracted in this case. Surprising results were obtained for α-particles impinging on the structured a-Ge contact. No coincident signals from the two adjacent strips caused by α-particles were observed. But a normally positive signal from one of the strips occasionally coincided with a negative signal from the other strip and vice versa. Using a cooled FET assembly mounted near a strip, an energy resolution of 0.78 keV [FWHM] for 60-keV photons was achieved and a slightly better resolution for lower energies. Even better energy resolutions will probably be possible, because the measuring setup was far from being optimized.