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

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