TUNNELING STATES IN NEUTRON-DISORDERED BULK SILICON

Measurements of the variation of the low-temperature (LT) ultrasonic v elocity and Raman scattering spectroscopy were performed on pure, bulk single-crystalline silicon, both unirradiated and irradiated with fas t-neutron doses up to 1.7 and 3.2x10(21) n/cm(2) (E>0.1 MeV). This irr adiation is found to transform the crystalline silicon structure into a partly disordered state. Previous LT studies on amorphous and partly disordered low-coordinated solids show the presence of low-energy exc itations, which can be described as quantummechanical tunneling states (TS's). The possible ''glassy'' behavior of highly coordinated solids , is, however, still under discussion. Our observations indicate the p resence of TS in neutron-irradiated bulk silicon. This result makes it possible to study TS in highly coordinated bulk solids.