V. Khomenkov

Analysis of the radiation hardness and charge collection efficiency of thinned silicon diodes

Due to their low depletion voltage, even after high particle fluences, improved tracking precision and momentum resolution and reduced material budget, thin substrates are one of the possible choices to provide radiation hard detectors for future high energy physics experiments. In the framework of the CERN RD50 Collaboration, we have developed p-n diode detectors on membranes obtained by locally thinning the silicon substrate by means of TMAH etching from the wafer back-side. Diodes of different shapes and sizes have been fabricated on 50-/spl mu/m and 100-/spl mu/m thick membranes and tested, showing a low leakage current (about 300 nA/cm/sup 3/) and, as expected, a very low depletion voltage (in the order of 1 V for the 50-/spl mu/m membrane). Radiation damage tests have been performed with 58-MeV Li ions at the SIRAD Irradiation Facility of the INFN National Laboratory of Legnaro, Italy, up to a fluence of 1.83 /spl times/ 10/sup 13/ Li/cm/sup 2/. Moreover, charge collection efficiency tests performed at INFN Firenze with a /spl beta/ particle source have been performed on both non-irradiated and irradiated samples. Results here reported confirm the advantages of thinned diodes with respect to standard ones in terms of low depletion voltage and charge collection efficiency even after the highest ion fluence.

Effect of Various Treatments on Light Emission Properties of Si-Rich-SiOx Structures

The effect of preparation conditions and annealing treatment on Si-rich-SiOx layers was investigated. It was observed that oxygen plays important role in the creation of light-emitting centres. It was found that the emission in the green-orange spectral range is connected with silicon oxide defects which contain dangling bonds. At the same time PL band in the infrared spectral range is caused by recombination of carriers in amorphous silicon or nanocrystalline one. It is shown that modification of defect content under various treatments gives the possibility to control the emission properties of the layers.

Stability of Emission Properties of Silicon Nanostructures

The aging process of silicon nanostructures obtained by magnetron sputtering and electrochemical etching is investigated by photoluminescence and Raman scattering methods. It is shown that oxidation of silicon crystallites takes place in both types of structures and results in appearance of additional emission bands. However the degree of oxidation in etched structures exceeds significantly this value for sputtered samples. It is found that the intensity and spectral position of the emission band caused by exciton recombination in Si crystallites do not change practically during aging in sputtered structures in contrast to etched ones. It is shown that the oxidation of silicon amorphous phase occur during aging in sputtered structures.

Bulk Radiation Damage Induced in Thin Epitaxial Silicon Detectors by 24 GeV Protons

Radiation hardness of silicon detectors based on thin epitaxial layer for the LHC upgrade was studied. No type inversion was observed after irradiation by 24 GeV protons in the fluence range (1.5–10)⋅1015 cm–2 due to overcompensating donor generation. After long-term annealing highly irradiated devices show decrease of effective doping concentration and then undergo type inversion. All mentioned means that thin epitaxial devices might be used for innermost layers of vertex detectors and need moderate cooling during beam off time. Properly chosen scenario might help to restore their working characteristics.