ABSTRACTMeV ion irradiation effects on semiconductor crystals, GaAs(100) and Si
(111) and on an insulating crystal CaF2 (111) have been studied
by the x-ray rocking curve technique using a double crystal x-ray
diffractometer. The results on GaAs are particularly interesting. The strain
developed by ion irradiation in the surface layers of GaAs (100) saturates
to a certain level after a high dose irradiation (typically
1015/cm2), resulting in a uniform lattice spacing
about 0.4% larger than the original spacing of the lattice planes parallel
to the surface. The layer of uniform strain corresponds in depth to the
region where electronic energy loss is dominant over nuclear collision
energy loss. The saturated strain level is the same for both p-type and
n-type GaAs. In the early stages of irradiation, the strain induced in the
surface is shown to be proportional to the nuclear stopping power at the
surface and is independent of electronic stopping power. The strain
saturation phenomenon in GaAs is discussed in terms of point defect
saturation in the surface layer.An isochronal (15 min.) annealing was done on the Cr-doped GaAs at
temperatures between 200° C and 700° C. The intensity in the diffraction
peak from the surface strained layer jumps at 200° C < T ≤ 300° C. The
strain decreases gradually with temperature, approaching zero at T ≤ 500°
C.The strain saturation phenomenon does not occur in the irradiated Si. The
strain induced in Si is generally very low (less than 0.06%) and is
interpreted to be mostly in the layers adjacent to the maximum nuclear
stopping region, with zero strain in the surface layer. The data on
CaF2 have been analysed with a kinematical x-ray diffraction
theory to get quantitative strain and damage depth profiles for several
different doses.
Solving the Puzzle of Nuclear Stopping Power
