CdTe prototype detector testing Anja Schubert The University of Melbourne 9 May 2011 Updates

Abstract Tested the performance of MCSS CdTe prototype. Charge collection efficiency Energy resolution Energy calibration Gain variation Tests run at SAXS&WAXS beamline Updates – Anja Schubert2 9 May 2011

3 2mm CdTe sensor 19 pixels in hexagonal array Signal is passed through preamp then delay-line shaper 8 channels connected read-out at once 14-bit ADC Labview interface Updates – Anja Schubert Charge preamp Pulse Shaper Output Buffer 9 May 2011 det I/p output

CdTe versus Si CdTe Z 48/52 e mobility cm2V/s h mobility cm2V/s E for e/h 4.4 to 4.5eV Higher CCE at high E Need to collect electrons Low h mobility leads to trapped positive charge! Si cm2V/s cm2V/s 3.62 eV Low CCE at high E Can collect holes or electrons 9 May 2011

Pixel Layout Hexagonal pixels with 20um gap. Indium bump bonds to connect to chip are formed on circular pads. Uniform electrode on back of sensor (Pt) 9 May

General set-up 9 May 2011 det X-stage Collimated beam 20x20um SAXS|WAXS table Z stage SAXS|WAXS table Z stage sensor Vbias = - 600V Sensor thickness 2mm

Charge Collection Maps Scanned over a 400x400um region in 20um steps. Beam size 20x20um 1000 triggers per point Peak of each waveform is histogrammed. From this the mean energy is calculated via a Gaussian fit for each point. Gives map of collection efficiency 9 May 2011 Drift timeSensor thickness Charge spread Bias Voltage Hole mobility

CCE map Scanned pixels are scaled to their central value (ie max) and summed 9 May

Charge Sharing From the CCE map we can calculate the charge sharing due to diffusion and drift. Repeated for all possible cross sections: σ = 23±5µm 9 May 2011

Energy Resolution Moved to center of pixel (calculate from CCE map). Gaussian fit to photo peak gives energy resolution as sigma/mean Energies 20keV,18keV,16keV,12keV and 8keV Energy resolution was found to be around 12% at 20keV. 9 May 2011 Incident Energy (keV) Mean Pulse Height (DAC) Standard Dev of Pulse Height (DAC) Energy Resolution Stdv/mean (%) noiseNA E=20keV

Energy Calibration Calibration for Pixel 4. 9 May 2011

Gain Variation E is 20keV Calculated from energy distribution at the center of each pixel Gain variation of 500% 9 May 2011 ChannelPixelMeanStd Dev

Summary Energy resolution was found to be around 12% at 20keV, decreasing as energy was lowered. Charge sharing due to drift and diffusion is up to 28um. Gain variation between pixels 500%. 9 May 2011