Improved neutron radiation hardness for Si detectors: application of low resistivity starting material and/or manipulation of N/sub eff/ by selective filling of radiation-induced traps at low temperatures

Abstract

Radiation-induced electrical changes in both space charge region (SCR) of Si detectors and bulk material (BM) have been studied for samples of diodes and resistors made on Si materials with different initial resistivities. The space charge sign inversion fluence (/spl Phi//sub inv/) has been found to increase linearly with the initial doping concentration (the reciprocal of the resistivity), which gives improved radiation hardness to Si detectors fabricated from low resistivity material. The resistivity of the BM, on the other hand, has been observed to increase with the neutron fluence and approach a saturation value in the order of hundreds k/spl Omega/ cm at high fluences, independent of the initial resistivity and material type. However, the fluence (/spl Phi//sub s/), at which the resistivity saturation starts, increases with the initial doping concentrations and the value of /spl Phi//sub s/ is in the same order of that of /spl Phi//sub inv/ for all resistivity samples. Improved radiation hardness can also be achieved by the manipulation of the space charge concentration (N/sub eff/) in SCR, by selective filling and/or freezing at cryogenic temperatures the charge state of radiation-induced traps, to values that will give a much smaller full depletion voltage. Models have been proposed to explain the experimental data.