Optical and structural properties of InAs nanocrystals fabricated by co-imp
lantation of In and As ions in Si-c(1 0 0), followed by thermal annealing a
re investigated. In the first sample named Si/AsIn the implantation of As i
ons was followed by In ion implantation, whereas in the second sample named
Si/InAs the order of implantation was inverted. RES spectra of these sampl
es taken before and after annealing show that the depth profiles of implant
ed ions depend strongly on the order of implantation. XRD measurements conf
irm the presence of InAs crystallites oriented along the crystallographic a
xes of the silicon matrix irrespective of the order of implantation. Low-te
mperature photoluminescence measurements show a large PL band in the region
0.83-1.03 eV for the sample Si/AsIn. No PL was observed in the sample Si/I
nAs. The optical absorption spectrum of Si/AsIn sample shows a large absorp
tion band in the region 0.4-0.9 eV, whereas the spectrum of sample Si/InAs
contains two distinct absorption bands at 0.45 eV and 0.8 eV. This may indi
cate a bimodal distribution of sizes of InAs nanocrystals in the Si/InAs sa
mple. The absorption and photoluminescence bands arise from the blueshifted
bandgap absorption/emission of InAs nanocrystals, this blueshift being dep
endent on the size of the nanocrystals. These results indicate that in the
case of As ions implanted first, the InAs nanocrystals are smaller than for
the case of In ions implanted first. This effect may be explained by the l
ow solubility of In ions in the silicon matrix, which results in agglomerat
ion of In ions during the implantation. When As ions are implanted afterwar
ds, the In clusters are partially transformed into InAs nanocrystals which
grow in size during the annealing. Hence, the order of ion implantation is
found to influence the size and distribution of the resultant nanocrystals,
as well as the optical properties of the samples obtained. (C) 2001 Elsevi
er Science B.V. All rights reserved.