Development of transmission Si(Li) detectors

During the development of double-sided microstructured Si(Li) detectors thin Lidoped contacts with effective thicknesses below 10 (mu)m could be created. The effective thickness was determined by evaluating the measured energy loss of (alpha)-particles entering the detector through the Li-doped contact. Extensive examinations have been performed to find the correlation between the effective thicknesses determined with the help of (alpha)-particles and the thicknesses based on the measured distribution of the Li-ions in the Li-diffused layers. Pronounced discrepancies were found in the relation between the effective thicknesses and the thicknesses of the removed layer during the thinning process. In any case, the effective thickness was considerably smaller than the thickness estimated from the distribution of the Li-ions. The dependence of the effective thickness on the bias voltage and the temperature was studied. A possible explanation of the relatively small effective thicknesses based on the internal electric field inside the Li-doped layer caused by the concentration gradient is presented. The technique to create Lidoped layers with an effective thickness smaller than 5 (mu)m is described. In this way, the transmission Si(Li) detectors with the effective dead layers being smaller than 0.1% of their thickness can be realized (patent is filed).