Structure‐related current transport and photoluminescence in SiO_xN_y and SiN_x based superlattices with Si nanocrystals

Abstract

Phone: þ7 495 939 4681, Fax: þ7 495 939 1566A comparative study of structural properties, photoluminescence and electrical conductivity of SiO x N y /SiO 2 , SiO x N y / Si 3 N 4 and SiN x /Si 3 N 4 superlattices is presented. The samples were prepared by plasma enhanced chemical vapor deposition and annealed at 1150 8C in order to produce arrays of silicon nanocrystals, with their formation being confirmed by X-ray diffraction analysis and photoluminescence spectroscopy. Reference samples without silicon nanocrystals were also fabricated by annealing of as-prepared films at a lower temperature (700 8C). All high temperature -annealed samples are characterized by similar photoluminescence spectra with the maxima in the range from 1.3 to 1.6 eV, which were attributed to Si nanocrystals. The peak position, as well as photoluminescence lifetime in the microsecond range, point to the quantum confined origin of the emission. Current-voltage measurements revealed an increase in conductivity by several orders of magnitude for the samples with Si nanocrystals in SiN x /Si 3 N 4 superlattices as compared to both SiO x N y /Si 3 N 4 and SiO x N y /SiO 2 films, as well as to low temperature annealed counterparts. The dependence of the conduction mechanism in superlattices on their structural properties is discussed.

Near-IR Emitting Si Nanocrystals Fabricated by Thermal Annealing of SiNx/Si3N4 Multilayers

“…Hence, we can assume that the most probable reason for the effect of Si NC coalescence demonstrated in Figure 1 is the small enough thickness of SiNx layers (1.6-2 nm), leading to an appearance of distinct intermixing regions. This trend is in full agreement with our previous observations of SL structure intermixing for SiOx and SiNx-based multilayers with ultrathin Si-rich layers [11,22,23].…”

“…Spectra are characterized by maxima in the near IR range (885-940 nm), which is not typical for Si NCs in Si 3 N 4 matrix, as mentioned above. Nevertheless, luminescence in this spectral region was also observed recently from similar SiN x /Si 3 N 4 SLs with Si NCs, but produced by different methods [10,23]. Moreover, bare theory of quantum confinement predicts the reduction of an energy gap (i.e., red shift) for Si nanocrystals with the decrease of confinement barriers, i.e., when nanocrystals are incorporated into Si 3 N 4 matrix instead of SiO 2 [4].…”

“…With respect to SL structures, matrix-related luminescence signal intensity may be reduced by decreasing the thickness of Si3N4 barriers, as demonstrated recently by an example of SiOxNy/Si3N4 hetero-SLs [6]. Indeed, in general, luminescence from Si NCs in SiNx/Si3N4 SLs with the peak energy at about 1.7 eV or below is observed, when Si3N4 barriers has the thickness under 2 nm [9,10,23]. On the opposite, in case of thicker barriers or SiNx monolayered films with Si NCs the position of PL peak is usually found in the spectral range above 1.7 eV [13,16,27].…”