Performance of bulk SiC radiation detectors

SiC is a wide-gap material with excellent electrical and physical properties that may make it an important material for some future electronic devices. The most important possible applications of SiC are in hostile environments, such as in car/jet engines, within nuclear reactors, or in outer space. Another area where the material properties, most notably radiation hardness, would be valuable is in the inner tracking detectors of particle physics experiments. Here, we describe the performance of SiC diodes irradiated in the 24 GeV proton beam at CERN. Schottky measurements have been used to probe the irradiated material for changes in I–V characteristics. Other methods, borrowed from III–V research, used to study the irradiated surface include atomic force microscope scans and Raman spectroscopy. These have been used to observe the damage to the materials surface and internal lattice structure. We have also characterised the detection capabilities of bulk semi-insulating SiC for α radiation. By measuring the charge collection efficiency (CCE) for variations in bias voltage, CCE values up to 100% have been measured

Developments in silicon detectors and their impact on LHCb physics measurements

The LHCb experiment is a high energy physics detector at the Large Hadron Collider (LHC) which will probe the current understanding of the Standard Model through precise measurements of CP violation and rare decays. The LHCb detector heavily depends on the silicon vertexing (VELO) sub-detector for excellent vertex and proper decay time resolutions. The VELO detector sits at a position of only 7 mm from the LHC proton beams. However, the proximity of the silicon sensors to the proton beams results in the detectors suffering radiation damage. Radiation damage results in three changes in the macroscopic properties of the silicon detector: an increase of the leakage current, a decrease in the charge collection efficiency, and changes in the operation voltage required to fully deplete the silicon detector of the free charge carriers. Due to this radiation damage, it is expected that a replacement or upgrade of the LHCb vertex detector will be required by 2010, only 3 years after the turn-on of the LHC. This thesis investigates possible scenarios for the VELO upgrade in 2010. There are two properties through which LHCb could gain from an upgraded VELO: increased statistics, and an improved proper time resolution. Increased statistics could be achieved by an increase in luminosity. Since the radiation damage is primarily caused by the primary interactions, an increase in luminosity would require silicon with a greater radiation tolerance. This thesis investigates Czochralski grown silicon as a possible radiation hard silicon. A detailed characterization has been performed on Czochralski silicon, including the use of the Transient Current Technique. The type inversion point of Czochralski silicon was investigated and no type inversion was measured in Czochralski silicon. The first test beam with a Czochralski strip detector read out with LHC speed electronics was performed and yielded promising results for the future application of Czochralski silicon. An increase in proper time resolution and impact parameter resolution could be achieved through the reduction of material in the detector, or through positioning the silicon closer to the proton beams. Research into repositioning the VELO is presented in this thesis and includes an investigation of possible designs that would position the first active silicon strip closer to the LHC beam. This is achieved by a redesign of the VELO sensor geometry with a reduced active inner radius. Results are then presented on the impact of this VELO design on the physics reach of the experiment

Guard Ring Width Impact on Impact Parameter Performances and Structure Simulations

The 1 mm guard ring structure of the VELO sensors has been simulated. The performance of the baseline design is considered and a design which improves the electric field characteristics proposed. Designs which would permit a reduced guard ring width, to 0.5 mm or better, are also discussed and shown to also have similarly good electric field performances. The effect of implementing these designs on the impact parameter resolution of LHCb is found to be better than 5 %. This design is currently being fabricated. Finally, a very different structure, the trench guard ring, is considered which would then allow an impact parameter resolution improvement of approximately 7 %

Super-radiation hard particle tracking at the CERN SLHC

The proposed upgrade of the CERN Large Hadron Collider to ten times brighter luminosity poses severe challenges to semiconductor detectors within the CERN experiments. We investigate a silicon "3-D" detector design for these conditions and semiconductors alternative to silicon, namely silicon carbide and gallium nitride, Charge collection measurements suggest some degree of additional radiation tolerance over conventional detector geometry and materials

Radiation-hard semiconductor detectors for SuperLHC.

An option of increasing the luminosity of the Large Hadron Collider (LHC) at CERN to 1035 cm−2 s−1 has been envisaged to extend the physics reach of the machine. An efficient tracking down to a few centimetres from the interaction point will be required to exploit the physics potential of the upgraded LHC. As a consequence, the semiconductor detectors close to the interaction region will receive severe doses of fast hadron irradiation and the inner tracker detectors will need to survive fast hadron fluences of up to above 1016 cm−2. The CERN-RD50 project “Development of Radiation Hard Semiconductor Devices for Very High Luminosity Colliders” has been established in 2002 to explore detector materials and technologies that will allow to operate devices up to, or beyond, this limit. The strategies followed by RD50 to enhance the radiation tolerance include the development of new or defect engineered detector materials (SiC, GaN, Czochralski and epitaxial silicon, oxygen enriched Float Zone silicon), the improvement of present detector designs and the understanding of the microscopic defects causing the degradation of the irradiated detectors. The latest advancements within the RD50 collaboration on radiation hard semiconductor detectors will be reviewed and discussed in this work