Production of detector-grade silicon using high-current electron accelerators

Abstract

With the development of new silicon detectors (SD) with a large working-surface area and depletion-region thickness [13], the requirements on starting-material quality have risen [4, 5]. Along with high resistivity p and charge-carrier lifetime T, homogeneity of the electrophysical properties of single-crystal silicon with large ingot diameters is acquiring principal importance. The acceptable resistivity fluctuation 6,0 over the volume of ingots of detector silicon with a diameter of greater than 50 mm is =20% at a nominal 3-10 kQ .cm. High-resistivity homogeneous silicon cannot be produced by conventional metallurgical methods, due to large fluctuations 6,0 and a small yield of single crystals with specified p [6]. Improvement of the volume homogeneity of resistivity and more-accurate control of the charge-carrier concentration and it space distribution are achieved by nuclear doping of the silicon by a phosphorous donor impurity or an aluminum acceptor impurity and irradiation of the starting single crystals by neutrons or gamma quanta, respectively [7]. The promise of the use of neutron-doped silicon in various types of SDs has been shown in some publications 12-5, 8]. Here, we shall present the results of a study of nuclear doping by means of bremsstrahlung gamma quanta [7, 9-11] to produce detector-grade silicon.