Depth distribution of luminescent Si nanocrystals in Si implanted SiO2 films on Si

Abstract

Depth-resolved measurements of the photoluminescence of Si implanted and annealed SiO 2 films on Si have been performed to determine the depth distribution of luminescent Si nanocrystals. Si nanocrystals with diameters ranging from ϳ2 to 5 nm were formed by implantation of 35 keV Si ions into a 110-nm-thick thermally grown SiO 2 film on Si͑100͒ at a fluence of 6ϫ10 16 Si/cm 2 , followed by a thermal anneal at 1100°C for 10 min. The photoluminescence spectrum is broad, peaks at ϭ790 nm, and contains contributions from both recombination of quantum confined excitons in the nanocrystals and ion-implantation-induced defects. By chemical etching through the SiO 2 film in steps and analyzing the changes in the photoluminescence spectrum after each etch step, the depth from which each of the two luminescence features originate is determined. The etch rate of the oxide, as derived from Rutherford backscattering spectrometry data, varies from 1.3 nm/s in the regions of small excess Si to 0.6 nm/s at the peak of the concentration profile ͑15 at. % excess Si͒. It is found that the defect luminescence originates from an ϳ15-nm-thick near-surface region. Large nanocrystals luminescing at long wavelengths ͑ ϭ900 nm͒ are mainly located in the center of the film, where the Si concentration is highest ͑48 at. %͒. This is corroborated by transmission electron microscopy that shows a high density of Si nanocrystals in the size range of 2-5 nm in the center of the film. The largest density of small luminescent nanocrystals ͑ ϭ700 nm͒, not detectable by electron microscopy is found near the SiO 2 surface and the SiO 2 /Si interface. This is attributed to either the fact that the surface and the SiO 2 /Si interface affect the Si nanocrystal nucleation kinetics in such a way that small nanocrystals are preferentially formed in these regions, or an optical interaction between nanocrystals of different sizes that quenches the luminescence of small nanocrystals in the center of the film.

Enhanced Radiative Emission Rate and Quantum Efficiency in Coupled Silicon Nanocrystal-Nanostructured Gold Emitters

“…The sizes of the nc-Si produced from the Gaussian ion implantation profile, were inferred from the variation of average PL emission wavelength with D, due to their size-dependent exciton emission energies, and found to be depthdependent. The measured trends indicated that smaller nanocrystals formed in the wings of the implanted excess Si + distribution, consistent with previous observations by Brongersma et al 6 The reference sample PL intensity, I PLref , was measured for each D, and the luminescence intensities were found to be consistent with a Gaussian nc-Si distribution centered at 19.2 ± 0.1 nm from the unetched surface. The separation distance between the quartz surface and the peak of the Si nanocrystal distribution at each step is therefore equal to (19.2 nm -D).…”

Excitation of surface plasmons at aSiO2∕Aginterface by silicon quantum dots: Experiment and theory

“…The error bars are calculated by taking into account the straggle of the Si depth profile and assuming a symmetric spread of Si QDs around the center of the distribution. 34 The decay rate enhancement by the Ag is then a factor 2.1± 0.1, and is mostly due to the additional SP decay channel that constitutes 60% of the total decay rate. Experimentally, the decay rate enhancement derived in Sec.…”

Tailoring the surface density of silicon nanocrystals embedded in SiOx single layers

“…1,2 Recently, it has been proposed to use them in solar cells for down-conversion, to generate multi-excitons or as a top absorber in multifunction solar systems. [3][4][5][6][7] Several different methods for fabricating Si-NCs, all compatible with the semiconductor industry standards, have been developed, such as ion implantation, 8 cosputtering, 9 or plasma enhanced or low pressure chemical vapor deposition (CVD). 10 Even so, all these techniques face difficulties in accurately controlling the Si-NCs size and density, leading to a certain degree of uncertainty in interpreting how the actual Si-NCs morphology affects their electronic properties.…”

“…Many efforts have been put so far to control the Si-NCs size, either by controlling the silicon concentration, the postdeposition thermal process [8][9][10] or limiting the thickness of SiO x layers between SiO 2 stoichiometric barriers (as the one proposed by Zacharias et al 11 ). Nevertheless, only few works can be found in literature dedicated to control and analyze the Si-NC areal density in similar systems.…”