Orientation and temperature dependence of electron damage in n-type germaniun

The energy dependence of defect production in n-type Ge has been studied at 78°K and 269°K for electron irradiation parallel to 〈111〉 and 〈100〉 crystallographic directions. Up to 900 kev, irradiation in the 〈111〉 direction results in greater defect production than irradiation parallel to 〈100〉. Damage production is higher at 269°K than at 78°K, but the orientation dependence is much smaller. The orientation effect vanishes at 340 kev. The maximum ratio between 〈111〉 and 〈100〉 damage production is found near 450 kev; a reversal occurs near 900 kev. It is suggested that the observed isotropic damage production at the lowest energy for which defect production can be detected may be an indication that there exists a lower displacement threshold corresponding to a nearest interstitial site along the 〈111〉 direction as postulated by Kohn.