Damaged regions in neutron-irradiated and ion-bombarded Ge and Si

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Abstract
The formation of amorphous or crystalline damaged regions by ion bombardment or neutron irradiation of Ge and Si is discussed. Several experiments have demonstrated that Ge and Si become amorphous when bombarded to high fluences with ions of 20–200 keV energy, but remain crystalline after low ion fluences (14/cm2) or after fission neutron irradiations up to very high fluences. The present results indicate that a fission neutron fluence of 5 × 1035 n/cm2 at ∼50 °C and at a flux of 6 × 1012 n/cm2/sec produces no amorphism in Ge or Si, but that microcrystals appear after annealing at 450 °C. It is concluded that the individual damaged regions produced by high-energy ions or by primary knock-on atoms from fission neutron collisions are crystalline. When these damaged regions are created rapidly enough so that overlap occurs before appreciable annealing of point defects takes place, the damaged regions become amorphous. The critical defect concentration required for spontaneous transformation to amorphism is estimated to be 0.02.