M. Valentan

Measuring doping profiles of silicon detectors with a custom-designed probe station

Silicon detectors are often used in High Energy Physics (HEP) experiments as tracking and vertexing devices. Many scientific institutes are equipped with setups able to electrically characterize those detectors e.g. for quality assurance reasons. Such probe stations can be easily extended to measure resistivities and doping profiles in the bulk material and in doped regions by using the Spreading Resistance Probe (SRP) technique. After an introduction to the method, this paper describes how an existing probe station, that has been used for electrical measurements on strip detectors, has been modified to perform SRP measurements. The presented results prove that the method is reliable and capable of characterizing doping regions as thin as one micron. Beside profiling implants, SRP measurements have the potential to deliver the basis for investigations of bulk material defects in heavily irradiated samples.

The 'LiC Detector Toy' program

LiC is a simple but powerful and flexible software tool, written in MatLab, for basic detector design studies (geometries, material budgets) by determining the resolution of reconstructed track parameters. It is based on a helix track model including multiple scattering, and consists of a simplified simulation of the detector followed by track reconstruction using the Kalman filter. After a short description of LiCs main characteristics, we demonstrate its capabilities by applying this tool in a performance study of the LDC and SiD detector concepts at the International Linear Collider (ILC).

Backside doping profiles of irradiated silicon detectors

Silicon detectors are used in High Energy Physics (HEP) experiments as tracking and vertexing devices. The damage caused by radiation is of special interest for sensors to be used at the HL-LHC. The doping profiles of highly irradiated sensors can neither be measured with common capacitance voltage methods nor with methods of chemical analysis. Nevertheless, they need to be known for damage modelling or for simulations of the sensor performance. In this paper it is shown that highly neutron irradiated doping profiles can be measured by using a spreading resistance probe technique. It turned out that the implantation depth of the profiles of active dopants decreases with increasing fluences.

Comparison of n-side strip isolation methods for silicon sensors

Precision experiments at electron-positron-colliders and b-factories demand high position resolution and low material budget for precise particle tracking. These requirements are fulfilled by thin double-sided silicon detectors (DSSDs). However, due to the low signals of thin sensors a careful sensor design is required in order to achieve high charge collection efficiency. In this paper we investigate the p-stop and the p-spray blocking method for strip isolation on the n-side of DSSDs with n-type bulk. We compare three different p-stop patterns: the common p-stop, the atoll p-stop and a combined p-stop pattern, whereas for every pattern four different geometric layouts are considered. Test sensors featuring these p-stop patterns and the p-spray blocking method were tested in a 120 GeV/c hadron beam at the Super Proton Synchrotron (SPS) at CERN (Geneva, Switzerland), where one variant of the atoll p-stop pattern performed best. The results of these tests are used to design the DSSDs for the Belle II experiment at KEK (Tsukuba, Japan).

Electronics and mechanics for the Silicon Vertex Detector of the Belle II experiment

A major upgrade of the KEK-B factory (Tsukuba, Japan), aiming at a peak luminosity of 8 × 1035cm−2s−1, which is 40 times the present value, is foreseen until 2014. Consequently an upgrade of the Belle detector and in particular its Silicon Vertex Detector (SVD) is required. We will introduce the concept and prototypes of the full readout chain of the Belle II SVD. Its APV25 based front-end utilizes the Origami chip-on-sensor concept, while the back-end VME system provides online data processing as well as hit time finding using FPGAs. Furthermore, the design of the double-sided silicon detectors and the mechanics will be discussed.

Comparing Spreading Resistance Profiling and C-V characterisation to identify defects in silicon sensors

The quality and functionality of a silicon sensor strongly depends on the effective doping concentration of the active silicon bulk. The creation of additional defects, by certain steps in the production or through irradiation in a particle beam, can heavily influence its performance. Several methods exist to characterise the bulk material for a silicon sensor. C-V characterisation is a widely implemented, non-destructive method to extract the depth profile of Neff. A technique which is rarely used at laboratories developing silicon sensors is Spreading Resistance Profiling (SRP) which directly measures the resistivity of the silicon. We will show, that a comparison of measurements from these two methods can yield important information on the defect concentration in the bulk of the silicon. To demonstrate the technique, we investigated a sensor material where the active region was reduced using a deep diffusion process which is assumed to create additional defects in the bulk.

Radiation Field Unfolding at the Free Electron Laser in Hamburg (FLASH) using a Genetic Algorithm

In Summer 2005, a high brilliance, vacuum ultraviolet (lambda=13 nm) free electron laser named FLASH (free electron laser in Hamburg) commenced its routine operation at DESY in Hamburg. The FLASH is driven by a 700 MeV electron linac based on high-purity superconducting Niobium cavities developed by the TESLA Technology collaboration at DESY. The gamma radiation doses along the containment tank walls of the accelerator modules 4 and 5 of the electron linac were evaluated using radiochromic films during its routine operation. This paper highlights a genetic algorithm (GA) developed by us in order to unfold the dosimeter readings. The unfolded data were used to inverse calculate the radiation source strength at the cavities, thereby quantifying the field emission induced radiation produced by each individual cavity belonging to the accelerator module.