Shifts of dilute Pt impurities in amorphous Si by ion irradiation

Abstract

Measurements have been made of shifts and broadenings of dilute Pt impurities in amorphous Si, caused by irradiation with heavy ions. The impurities were layers of about 5 Å buried at depths of about 500 Å. The samples were irradiated at 90 K with Ar, Kr and Xe ions with energies of 110, 40 and 300 keV respectively and analyzed by backscattering spectrometry. Shifts were deduced from changes in the position of the signal from the mixed impurity layer relative to the signal from a second impurity layer buried beyond the range of the incident ions. Broadenings were quantified as half widths deduced from the increases in the variances of the impurity signals. 40 keV Kr ions did not reach the top impurity layer in significant numbers and no shifts or broadenings were observed. 110 keV Ar ions and 300 keV ions mostly penetrated past the shallow impurity layer and caused shifts of the mean of the impurity distribution away from the surface of the sample. The magnitudes were (80±40) Å for 5 × 10 16 Ar ions/cm 2 and (110±50) Å for 1 × 10 16 Xe ions/cm 2, and appeared to increase with irradiation fluence. The direction of these shifts is the opposite of that predicted for collisional mixing by recoiling matrix atoms. The squares of the half widths of the profile broadenings were about 50 times greater than those predicted by collisional theory, assuming mixing by matrix recoils is suppressed.