Properties of InAs nanocrystals in silicon formed by sequential ion implantation

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.