Characterisation of Ge micro-strip sensors with a micro-focused X-ray beam

Abstract

Germanium micro-strip sensors were selected as the sensor technology to take data in energy dispersive X-ray spectroscopy experiments at the Extremely Brilliant Source (EBS) in Grenoble (FR). It is important for this experimental technique to use sensors with a large uniform area and a fine pitch. The former determines the range of energy detectable with a single sensor. The latter improves spectral resolution. A high stopping power is also important to perform studies with hard X-rays.The device under test in this measurement was a germanium micro-strip sensor made of 1024 strips with 50μm pitch. The bulk was 1.5 mm thick. The sensor was assembled into a prototype cryostat part of the XH detector system. The device was tested at the B16 beamline at the Diamond Light Source (DLS) in Didcot (UK). The objective of the test-beam was to characterise charge-sharing between strips. In fact, this effect limits the spectral resolution of the device.To carry out this test, the sensor was scanned over a subset of strips with micro-focused X-rays under different settings. These were beam energy and intensity, sensor temperature and bias voltage. Results are presented in this paper. It was measured that the full width half maximum of the charge-sharing profile across different strips was ∼90μm for settings which were indicative of the experimental conditions at the EBS. This was a signal current per unit area on the sensor of ∼1.66×10−8 A/μm2, a bias voltage of −180 V and a temperature of −159 oC.