Efficacy of annealing and fabrication parameters on photo-response of SiGe in TiO₂ matrix

Abstract

SiGe nanoparticles dispersed in a dielectric matrix exhibit properties different from those of bulk and have shown great potential in devices for application in advanced optoelectronics. Annealing is a common fabrication step used to increase crystallinity and to form nanoparticles in such a system. A frequent downside of such annealing treatment is the formation of insulating SiO 2 layer at the matrix/SiGe interface, degrading the optical properties of the structure. An annealing process that could bypass this downside would therefore be of great interest. In this work, a short-time furnace annealing of a SiGe/TiO 2 system is applied to obtain SiGe nanoparticles without formation of the undesired SiO 2 layer between the dielectric matrix (TiO 2 ) and SiGe. The structures were prepared by depositing alternate layers of TiO 2 and SiGe films, using directcurrent magnetron sputtering technique. A wide range spectral response with a responsethreshold up to ∼1300 nm was obtained, accompanied with an increase in photo-response of more than two-orders of magnitude. Scanning electron microscopy, transmission electron microscopy, energy-dispersive x-ray spectroscopy and grazing incidence x-ray diffraction were used to analyze the morphological changes in respective structures. Photoconductive properties were studied by measuring photocurrent spectra using applied dc-voltages at various temperatures.

Influence of SiGe Nanocrystallization on Short-Wave Infrared Sensitivity of SiGe–TiO2 Films and Multilayers

“…XTEM and HRTEM details (Figure c,d) show that the columnar NC arrangement is formed by SiGe and TiO 2 NCs separated by an amorphous matrix rich in SiO 2 . Similar structures were reported in ref . However, we did not find any trace of mixed oxide as (GeTi)­O 2 NCs embedded in a Si­(Ti)­O 2 amorphous matrix as in the case of our previous reports on films of Ge NCs in a matrix of TiO 2 NCs. , Here, in the samples F , the presence of Si looks to be essential to make the difference to the stability of SiGe NCs.…”

“…One can see that the multilayers are photosensitive up to 1600 nm for both 100 and 300 K measurement temperatures due to the light absorption in Ge-rich SiGe NCs (77 ± 16% Ge content). Consequently, within this paper, the sensitivity limit of SiGe/TiO 2 multilayers and SiGe–TiO 2 films (1600 and 1700 nm, respectively) is much extended in SWIR in comparison with ref reporting a photoresponse threshold of up to 1300 nm for SiGe/TiO 2 multilayers or to ref in which spectral sensitivity up to 1250 nm was obtained in films of Ge NCs embedded in TiO 2 . The stabilization of SiGe alloy NCs against fast Ge diffusion ensures a SWIR-extended spectral photocurrent due to photocarrier generation in Ge-rich SiGe NCs.…”

“…The SiGe NC-based structures that are usually reported in the literature are either thin films of SiGe only , or thin films and multilayer structures with SiGe NCs embedded in different oxide matrices, ,− the most commonly used being SiO 2 . Using films of the polycrystalline SiGe alloy only is disadvantageous because of the nonradiative recombination centers formed at the crystal grain boundaries, decreasing the photogenerated carrier density.…”

Fabrication and characterization of Si1−xGex nanocrystals in as-grown and annealed structures: a comparative study

“…The size of 12.5 nm correspond in fact to the diameter of the SiGe ellipsoid plus the thickness of the SiGeO oxide cover-layer, i.e., each SiGe crystallite is covered by 2–3 nm of SiGeO oxide, looking like a core–shell particle. An elemental mapping over a structure (TiO 2 /SiGe/TiO 2 ) 3 annealed at 600 °C in our previous study [37], showed a similar columnar self-assembly of NCs. The analysis showed a well-defined mapping of Si, Ge and Ti (/TiO 2 ) with a small fraction of oxygen observed in the SiGe layer.…”

“…Additionally, the annealing in H 2 /N 2 ambient results in a blue-shift of peak N and is limited as H 2 tends to leave the structure when annealed above 400 °C. To further elucidate the origin of peaks I and N, further studies [22,37] of spectral analysis at varying measurement temperatures (80–300 K) and at varying applied bias (1–11 V) were carried out.…”