Analysis of the charge collection process in solid state X-ray detectors [Elektronische Ressource] / vorgelegt von Nils Kimmel

Nils Kimmel

Sujets

• Physik

Informations

• Publié par: universitat_siegen
• Publié le: 01 janvier 2009
• Nombre de lectures: 29
• Langue: Deutsch
• Poids de l'ouvrage: 12 Mo

Extrait

Analysis of the charge collection process
in solid state X–ray detectors
DISSERTATION
zur Erlangung des Grades eines Doktors
der Naturwissenschaften
vorgelegt von
Dipl.-Phys. Nils Kimmel
geb. am 5 April 1976 in Castrop-Rauxel
eingereicht beim Fachbereich Physik
der Universitat¨ Siegen
Siegen, 2008Tag der mundlichen Prufung: 12.02.2009¨ ¨
Erster Gutachter: Prof. Dr. Lothar Struder (Arbeitsgruppe Detektorphysik¨
und Elektronik)
Zweiter Gutachter: Prof. Dr. Ullrich Pietsch (Arbeitsgruppe Festk¨orperphysik)Kurzfassung
PhysikmitR¨ontgenstrahlenbefasstsichsowohlmitgrosskaligenStruktureninderRon¨ tgenastro-
nomie, als auch mit kleinskaligen Phanomenen bei Strukturanalysen mit Synchrotronstrahlung.¨
InbeidendergenanntenBereichewerdenbildgebendeSensorenben¨otigt,diezus¨atzlich alsSpek-
trometerimEnergiebereichvon0.1keVbis20.0keVarbeiten.UrsprunglichwurdenpnCCDsam¨
Halbleiterlabor der Max–Planck–Institute fu¨r Physik und extraterrestrische Physik entwickelt,
um ein bildgebendes Spektrometer fur die Rontgenastronomiemission XMM–Newton der ESA¨ ¨
bereitzustellen.Das pnCCDisteinDetektor mitPixelstruktur,dervom Infrarotenub¨ eroptische
und UV–Strahlung bis hin zu R¨ontgenstrahlung empfindlich ist.
Diese Arbeit beschreibt die Bewegung von Signalelektronen vom Zeitpunkt ihrer Erzeugung bis
zur Sammlung in den Speicherzellen der Pixelstruktur. Zur experimentellen Untersuchung von
pnCCDs wurdeein Lochraster eingesetzt, das deren Oberflac¨ he mit hoher r¨aumlicher Auflo¨sung
abtastet. Mit Hilfe von numerischen Bauelementesimulationen stand ein Werkzeug zur Model-
lierung der elektrischen Bedingungen in pnCCDs zur Verfug¨ ung.
Durch die Kombination der durchgefuhrten Experimente und Simulationen konnte ein Modell¨
fur¨ dieSignalladungsdynamikim Energiebereich von 0.7 keV bis 5.5 keV erstellt werden.Im all-
gemeineren Sinne hat die vorliegende Arbeit mittels eines physikalisches Modells das Verstand-¨
nis von pnCCDs erweitert. Die dazu entwickelten experimentellen und theoretischen Methoden
konnen auf jeden Detektor angewendet werden, der auf einem vollstandig verarmten Halbleiter-¨ ¨
substrat aufbaut.
Abstract
Physics with X–rays spans from observing large scales in X–ray astronomy down to small scales
inmaterialstructureanalyseswithsynchrotronradiation.Bothfieldsofresearchrequireimaging
detectors featuringspectroscopicresolutionforX–raysinanenergyrangeof0.1keVto20.0keV.
Originally driven by the need for an imaging spectrometer on ESA’s X–ray astronomy satellite
mission XMM-Newton, X–ray pnCCDs were developed at the semiconductor laboratory of the
Max–Planck–Institute. The pnCCD is a pixel array detector made of silicon. It is sensitive over
a wide band from near infrared– over optical– and UV–radiation up to X–rays.
This thesis describes the dynamics of signal electrons from the moment after their generation
until their collection in the potential minima of the pixel structure. Experimentally, a pinhole
array was used to scan the pnCCD surface with high spatial resolution. Numerical simulations
were used as a tool for the modeling of the electrical conditions inside the pnCCD. The results
predicted by the simulations were compared with the measurements.
Both, experiment and simulation, helped to establish a model for the signal charge dynamics
in the energy range from 0.7 keV to 5.5 keV. More generally, the presented work has enhanced
the understanding of the detector system on the basis of a physical model. The developed
experimental and theoretical methods can be applied to any type of array detector which is
based on the full depletion of a semiconductor substrate material.Contents
Overview 1
1 Introduction 3
1.1 Motivation.................................... 3
1.2 Basic semiconductor structures . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2.1 The pn-junction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2.2 TheMOS–capacitor .......................... 7
1.3 X–ray photon detection in silicon . . . . . . . . . . . . . . . . . . . . . . . 14
1.4 Charge storage and shift in three phase CCDs . . . . . . . . . . . . . . . . 16
1.5 pnCCD ..................................... 19
1.5.1 Fuldepletionofthedetectorvolume................. 19
1.5.2 Charge collection, storage and measurement in pnCCDs . . . . . . . 21
1.5.3 Readoutelectronics........................... 24
1.5.4 Applications for X–ray pnCCDs . . . . . . . . . . . . . . . . . . . . 26
2 pnCCD in detail 31
2.1 ThepixelarayofapnCCD.......................... 31
2.1.1 Structureandelectricdefinitionofapixel .............. 31
2.1.2 Thereadoutstructureofachannel.................. 35
2.2 Electricpotentialinthebulk.......................... 36
2.2.1 Driftanddiffusionofelectriccharge. 38
3 The mesh experiment 45
3.1 Functionprinciple................................ 45
3.1.1 Energy range and spatial resolution . . . . . . . . . . . . . . . . . . 47
3.2 Analysisofmeshmeasurementdata...................... 49
3.2.1 Determinationofthemeshgeometry................. 50
3.2.2 Reconstructionofthevirtualpixelmap................ 5
4 Measurements 61
4.1 Setup for the used pnCCDs . . . . . . . . . . . . . . . . . . . . . . . . . . 61
4.1.1 The Rosti facility . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61¨
4.1.2 pnCCDs used for measurements . . . . . . . . . . . . . . . . . . . . 63
ICONTENTS
4.1.3 meshasembly ............................. 64
4.2 Measurementprogram 67
4.2.1 Back side illumination . . . . . . . . . . . . . . . . . . . . . . . . . 68
4.2.2 Front side . . . . . . . . . . . . . . . . . . . . . . . . . 70
4.3 Standardanalysisandcalibrationofdata................... 72
4.3.1 Noiseandoffsetcalibration ...................... 73
4.3.2 Photoneventdetection......................... 75
4.3.3 Gain calibration and CTE correction . . . . . . . . . . . . . . . . . 76
4.3.4 Analysisoutput 78
5 ‘Mesh’ data analysis 81
5.1 Typesofreconstructedpixelmaps. 81
5.1.1 Eventtypemaps............................ 82
5.1.2 Photonresponsemaps. 85
5.2 Precisionofthegeneratedmaps........................ 89
5.2.1 Geometricalmeshparameters..................... 89
5.2.2 Error function model of the charge collection function . . . . . . . . 91
5.3 Analysisofthepixelresponse. 93
5.3.1 Locationofeventtypes. 94
5.3.2 Photonflux...............................101
5.3.3 Chargecolection............................108
6 Device simulations 115
6.1 Simulations of a pnCCD with 75 μmpixels..................18
6.1.1 Chargetransferdirection........................19
6.1.2 Linedirection..............................12
6.2 Simulationsofchargedriftanddiffusion ...................124
6.2.1 Simulationprinciple ..........................124
6.2.2 Electrondriftinthebulk.128
6.2.3 Numeric simulations of the charge cloud expansion . . . . . . . . . 133
7 Comparison of device simulations and analysis results 137
7.1 Evaluationofccfsimulations..........................137
7.1.1 75 μmpixelpnCCD138
7.1.2 51 μmpixelpnCCD139
7.1.3 Reconstruction of the photon conversion position . . . . . . . . . . 144
7.2 Separationprocesofachargecloud .....................149
7.3 Photon absorption in the front-side structure . . . . . . . . . . . . . . . . . 152
7.3.1 Electricpotentialatthefrontside...................153
7.3.2 Best fit parameters for the absorption model . . . . . . . . . . . . . 159
Conclusion 163
IIList of figures i
Literature v
IIIIVOverview
Physics with X–rays spans from observing large scales in X–ray astronomy down to small
scales in material structure analyses with synchrotron radiation. Both fields of research
require imaging detectors featuring spectroscopic resolution for X–rays in an energy range
of 0.1 keV to 20.0 keV. Originally driven by the need for an imaging spectrometer on ESA’s
X–ray astronomy satellite mission XMM-Newton, X–ray pnCCDs were developed at the
semiconductor laboratory of the Max–Planck–Institute (MPI-HLL). The pnCCD is a pixel
array detector made of silicon. It is sensitive over a wide band from near infrared– over
optical– and UV–radiation up to X–rays.
This thesis describes the dynamics of signal electrons from the moment after their gener-
ation until their collection in the potential minima of the pixel structure. Experimentally,
a pinhole array was used to scan the pnCCD surface with high spatial resolution. Numeri-
cal simulations were used as a tool for the modeling of the electrical conditions inside the
pnCCD. The results predicted by the simulations were compared with the measurements.
Both, experiment and simulation, helped to establish a model for the signal charge
dynamics in the energy range from 0.7 keV to 5.5 keV. The benefits from this analysis
approach are:
• Improvement of the spatial resolution of the detector. The conversion position of X–
ray photons can be reconstructed from signal charge measurements. The accuracy
of the reconstruction is only limited by the precision of a charge measurement.
• Better design capabilities for the definition of future pixel geometries. Pixel sizes
can now be adjusted for the optimum ratio of the spatial resolution to the spectral
resolution of the detector.
• Identification of insensitive regions in the