Design and First Tests of a Radiation-Hard Pixel Sensor for the European X-Ray Free-Electron Laser

The high intensity and high repetition rate of the European X-ray Free-Electron Laser, presently under construction in Hamburg, requires silicon sensors which can stand X-ray doses of up to 1 GGy for 3 years of operation at high bias voltage. Within the AGIPD Collaboration the X-ray-radiation damage in MOS Capacitors and Gate-Controlled Diodes fabricated by four vendors on high-ohmic n-type silicon with two crystal orientations and dif- ferent technological parameters, has been studied for doses between 1 kGy and 1 GGy. The extracted values of oxide-charge and surface-current densi- ties have been used in TCAD simulations, and the layout and technological parameters of the AGIPD pixel sensor optimized. It is found that the op- timized layout for high X-ray doses is significantly different from the one for non-irradiated sensors. First sensors and test structures have been de-livered in early 2013. Measurement results for X-ray doses of 0 to 10 MGy and their comparison to simulations are presented. They demonstrate that the optimization has been successful and that the sensors fulfill the required specifications

Investigation of X-ray induced radiation damage at the Si-SiO2 interface of silicon sensors for the European XFEL

Experiments at the European X-ray Free Electron Laser (XFEL) require silicon pixel sensors which can withstand X-ray doses up to 1 GGy. For the investigation of X-ray radiation damage up to these high doses, MOS capacitors and gate-controlled diodes built on high resistivity n-doped silicon with crystal orientations and produced by two vendors, CiS and Hamamatsu, have been irradiated with 12 keV X-rays at the DESY DORIS III synchrotron light source. Using capacitance/conductance-voltage, current-voltage and thermal dielectric relaxation current measurements, the surface densities of oxide charges and interface traps at the Si-SiO2 interface, and the surface-current densities have been determined as function of dose. Results indicate that the dose dependence of the surface density of oxide charges and the surface-current density depend on the crystal orientation and producer. In addition, the influence of the voltage applied to the gates of the MOS capacitor and the gate-controlled diode during X-ray irradiation on the surface density of oxide charges and the surface-current density has been investigated at doses of 100 kGy and 100 MGy. It is found that both strongly depend on the gate voltage if the electric field in the oxide points from the surface of the SiO2 to the Si-SiO2 interface. Finally, annealing studies have been performed at 60 and 80 degree C on MOS capacitors and gate-controlled diodes irradiated to 5 MGy and the annealing kinetics of oxide charges and surface current determined.Comment: 10 pages, 6 figures, 3 table

Radiation Induced Point and Cluster-Related Defects with Strong Impact to Damage Properties of Silicon Detectors

This work focuses on the investigation of radiation induced defects responsible for the degradation of silicon detectors. Comparative studies of the defects induced by irradiation with 60Co- rays, 6 and 15 MeV electrons, 23 GeV protons and 1 MeV equivalent reactor neutrons revealed the existence of point defects and cluster related centers having a strong impact on damage properties of Si diodes. The detailed relation between the microscopic reasons as based on defect analysis and their macroscopic consequences for detector performance are presented. In particular, it is shown that the changes in the Si device properties after exposure to high levels of 60Co- doses can be completely understood by the formation of two point defects, both depending strongly on the Oxygen concentration in the silicon bulk. Specific for hadron irradiation are the annealing effects which decrease resp. increase the originally observed damage effects as seen by the changes of the depletion voltage. A group of three cluster related defects, revealed as deep hole traps, proved to be responsible specifically for the reverse annealing. Their formation is not affected by the Oxygen content or Si growth procedure suggesting that they are complexes of multi-vacancies located inside extended disordered regions.Comment: 14 pages, 15 figure

Investigation of high resistivity p-type FZ silicon diodes after 60Co {\gamma}-irradiation

In this work, the effects of $^\text{60}$Co $\gamma$-ray irradiation on high resistivity $p$-type diodes have been investigated. The diodes were exposed to dose values of 0.1, 0.2, 1, and \SI{2}{\mega Gy}. Both macroscopic ($I$--$V$, $C$--$V$) and microscopic (Thermally Stimulated Current~(TSC)) measurements were conducted to characterize the radiation-induced changes. The investigated diodes were manufactured on high resistivity $p$-type Float Zone (FZ) silicon and were further classified into two types based on the isolation technique between the pad and guard ring: $p$-stop and $p$-spray. After irradiation, the macroscopic results of current-voltage and capacitance-voltage measurements were obtained and compared with existing literature data. Additionally, the microscopic measurements focused on the development of the concentration of different radiation-induced defects, including the boron interstitial and oxygen interstitial (B$_\text{i}$O$_\text{i}$) complex, the carbon interstitial and oxygen interstitial C$_\text{i}$O$_\text{i}$ defect, the H40K, and the so-called I$_\text{P}^*$. To investigate the thermal stability of induced defects in the bulk, isochronal annealing studies were performed in the temperature range of \SI{80}{\celsius} to \SI{300}{\celsius}. These annealing processes were carried out on diodes irradiated with doses of 1 and \SI{2}{\mega Gy} and the corresponding TSC spectra were analysed. Furthermore, in order to investigate the unexpected results observed in the $C$-$V$ measurements after irradiation with high dose values, the surface conductance between the pad and guard ring was measured as a function of both dose and annealing temperature

Investigation of the Boron removal effect induced by 5.5 MeV electrons on highly doped EPI- and Cz-silicon

This study focuses on the properties of the B$_\text{i}$O$_\text{i}$ (interstitial Boron~-~interstitial Oxygen) and C$_\text{i}$O$_\text{i}$ (interstitial Carbon~-~interstitial Oxygen) defect complexes by \SI{5.5}{\mega\electronvolt} electrons in low resistivity silicon. Two different types of diodes manufactured on p-type epitaxial and Czochralski silicon with a resistivity of about 10~$\Omega\cdot$cm were irradiated with fluence values between \SI{1e15}{\per\square\centi\meter} and \SI{6e15}{\per\square\centi\meter}. Such diodes cannot be fully depleted and thus the accurate evaluation of defect concentrations and properties (activation energy, capture cross-section, concentration) from Thermally Stimulated Currents (TSC) experiments alone is not possible. In this study we demonstrate that by performing Thermally Stimulated Capacitance (TS-Cap) experiments in similar conditions to TSC measurements and developing theoretical models for simulating both types of B$_\text{i}$O$_\text{i}$ signals generated in TSC and TS-Cap measurements, accurate evaluations can be performed. The changes of the position-dependent electric field, the effective space charge density $N_\text{eff}$ profile as well as the occupation of the B$_\text{i}$O$_\text{i}$ defect during the electric field dependent electron emission, are simulated as a function of temperature. The macroscopic properties (leakage current and $N_\text{eff}$) extracted from current-voltage and capacitance-voltage measurements at \SI{20}{\celsius} are also presented and discusse

Measurements of charge carrier mobilities and drift velocity saturation in bulk silicon of 〈111〉 and 〈100〉 crystal orientation at high electric fields

The mobility of electrons and holes in silicon depends on many parameters. Two of them are the electric field and the temperature. It has been observed previously that the mobility in the transition region between ohmic transport and saturation velocities is a function of the orientation of the crystal lattice. This paper presents a new set of parameters for the mobility as function of temperature and electric field for and crystal orientation. These parameters are derived from time of flight measurements of drifting charge carriers in planar p^+nn^+ diodes in the temperature range between -30{\deg}C and 50{\deg}C and electric fields of 2x10^3 V/cm to 2x10^4 V/cm.Comment: revised version after peer revie

Results on defects induced by Co-60 gamma irradiation in standard and oxygen enriched silicon

Radiation-induced defects in silicon diodes were investigated after exposure to high doses of 60 Co gamma irradiation, using Deep Level Transient Fourier Spectroscopy and Thermally Stimulated Current methods. The main focus was on differences between standard and oxygen-enriched material and the impact of the observed defect generation on the diode properties. Two close to mid gap trapping levels and a bi-stable donor level have been found to be responsible for the main macroscopic changes both in standard and oxygen-enriched float zone diodes