The Energy Loss by Charged Particles in Silicon as a Function of Track Orientation

It is important to know the orientation of the crystal axis of silicon semiconductor detectors when they are used for the detection of energetic charged particles in stacked arrays and the particles are expected to traverse all of the detectors. It has been observed that particles that pass through the crystal along the directions of crystal planes or axes lose less energy than those in other directions. This anomalous energy loss spoils the response characteristics of the detector. Various experiments have demonstrated that the penetrating particles tend to move along crystal planes or axes by a process of correlated multiple-coulomb scattering. The experimental evidence for these anomalous characteristics will be reviewed and the degrading effects on the discrimination ability of mass-discrimination detector-systems will be shown. Mass distribution curves were taken for protons, deuterons, tritons, as well as He3 and alpha particles in the 20 to 40 MeV region with a thin silicon¿E detector oriented with the (111), (110) and other axis parallel to the penetrating particle direction. The mass separation is appreciably improved when the crystal is oriented so that the direction of the penetrating particles is well away from any of the major crystal planes or axes.