ZnTe precipitates formed in SiO2 by sequential implantation of Zn+ and Te+ ions

Ion implantation is a versatile tool for the formation of compound semiconductor nanocrystal precipitates in a host medium with the ultimate goal to form quantum dots for use in device technology. Low dose (1 × 1016 cm−2) implantations of tellurium and zinc ions have been performed in a 250 nm thick SiO2 layer thermally grown on 〈1 1 1〉 silicon. Their respective energies (180 and 115 keV) have been chosen to produce 5–10 at.% profiles overlapping at a mean depth of about 100 nm. Subsequent thermal treatments at 700 and 800 °C lead to the formation of nanometric precipitates of the compound semiconductor ZnTe. Their size, crystalline structure and depth distribution have been studied as a function of annealing temperature using transmission electron microscopy (TEM) and Rutherford backscattering spectrometry. For the lowest temperature the TEM images shows a cloudy band of ZnTe, but for the highest temperature, the ZnTe nanocrystals are self organized into two layers parallel to the surface. Their mean diameter ranges between 4 and 30 nm, as a function of annealing temperature.