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Depth of interaction and bias voltage depenence of the spectral response in a pixellated CdTe detector operating in time-over-threshold mode subjected to monochromatic X-rays

DOI: 10.1088/1748-0221/7/03/C03002 DOI Help

Authors: E. Frojdh (Mid Sweden University, Sweden) , C. Frojdh (Mid Sweden University, Sweden) , E. N. Gimenez (Diamond Light Source) , D. Maneuski (University of Glasgow, U.K.) , J. Marchal (Diamond Light Source) , B. Norlin (Mid Sweden University, Sweden) , V. O'shea (University of Glasgow, U.K.) , G. Stewart (University of Glasgow, U.K.) , R. Modh Zain (University of Glasgow, U.K.) , G. Thungstrom (Mid Sweden University, Sweden) , H. Wilhelm (Diamond Light Source)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Instrumentation , VOL 7

State: Published (Approved)
Published: March 2012

Open Access Open Access

Abstract: High stopping power is one of the most important figures of merit for X-ray detectors. CdTe is a promising material but suffers from: material defects, non-ideal charge transport and long range X-ray fluorescence. Those factors reduce the image quality and deteriorate spectral information. In this project we used a monochromatic pencil beam collimated through a 20 mu m pinhole to measure the detector spectral response in dependance on the depth of interaction. The sensor was a 1mm thick CdTe detector with a pixel pitch of 110 mu m, bump bonded to a Timepix readout chip operating in Time-Over-Threshold mode. The measurements were carried out at the Extreme Conditions beamline I15 of the Diamond Light Source. The beam was entering the sensor at an angle of similar to 20 degrees to the surface and then passed through similar to 25 pixels before leaving through the bottom of the sensor. The photon energy was tuned to 77keV giving a variation in the beam intensity of about three orders of magnitude along the beam path. Spectra in Time-over-Threshold (ToT) mode were recorded showing each individual interaction. The bias voltage was varied between -30V and -300V to investigate how the electric field affected the spectral information. For this setup it is worth noticing the large impact of fluorescence. At -300V the photo peak and escape peak are of similar height. For high bias voltages the spectra remains clear throughout the whole depth but for lower voltages as -50V, only the bottom part of the sensor carries spectral information. This is an effect of the low hole mobility and the longer range the electrons have to travel in a low field.

Journal Keywords: Beams; Cadmium Tellurides; Cdte Semiconductor Detectors; Charge Transport; Electric Fields; Escape Peaks; Fluorescence; Images; Interactions; Monochromatic Radiation; Pitches; Readout Systems; Sensors; Spectra; Spectral Response; Stopping Power; Surfaces

Subject Areas: Technique Development

Instruments: I15-Extreme Conditions

Added On: 08/10/2012 14:25

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