Si-rich Al2O3 films grown by RF magnetron sputtering: structural and photoluminescence properties versus annealing treatment

International audienceSilicon-rich Al2O3 films (Six(Al2O3)1−x) were co-sputtered from two separate silicon and alumina targets onto a long silicon oxide substrate. The effects of different annealing treatments on the structure and light emission of the films versus x were investigated by means of spectroscopic ellipsometry, X-ray diffraction, micro-Raman scattering, and micro-photoluminescence (PL) methods. The formation of amorphous Si clusters upon the deposition process was found for the films with x ≥ 0.38. The annealing treatment of the films at 1,050°C to 1,150°C results in formation of Si nanocrystallites (Si-ncs). It was observed that their size depends on the type of this treatment. The conventional annealing at 1,150°C for 30 min of the samples with x = 0.5 to 0.68 leads to the formation of Si-ncs with the mean size of about 14 nm, whereas rapid thermal annealing of similar samples at 1,050°C for 1 min showed the presence of Si-ncs with sizes of about 5 nm. Two main broad PL bands were observed in the 500- to 900-nm spectral range with peak positions at 575 to 600 nm and 700 to 750 nm accompanied by near-infrared tail. The low-temperature measurement revealed that the intensity of the main PL band did not change with cooling contrary to the behavior expected for quantum confined Si-ncs. Based on the analysis of PL spectrum, it is supposed that the near-infrared PL component originates from the exciton recombination in the Si-ncs. However, the most intense emission in the visible spectral range is due to either defects in matrix or electron states at the Si-nc/matrix interface

Comparative Investigation of Structural and Optical Properties of Si-Rich Oxide Films Fabricated by Magnetron Sputtering

International audienceRF magnetron sputtering of two separate silicon and oxide (SiO2 or Al2O3) targets in pureargon plasma was used for deposition of Six(SiO2)1-x and Six(Al2O3)1-x films with x=0.15-0.7 onlong fused quarts substrate. The effect of post-fabrication treatments on structural and light emittingproperties of the films with different x values was investigated by means of Raman scattering,electron paramagnetic resonance and X-ray diffraction as well as by photoluminescence (PL)methods. The formation of amorphous Si clusters upon deposition process was found for the bothtypes of films. The annealing treatment at 1150°C during 30 min results in formation of Sinanocrystallites (Si-ncs). The latter were found to be larger in Six(Al2O3)1-x films than that inSix(SiO2)1-x counterparts with the same x values and are under tensile stresses. The investigation ofphotoluminescence properties of annealed films of both types revealed the appearance of visiblenearinfrared light emission. The Six(SiO2)1-x films demonstrated one broad PL band which peakposition shifts gradually to from 1.4 eV to 1.8 eV with the x decrease. Contrary to this, for theSix(Al2O3)1-x films two overlapped PL bands were observed in the 1.4-2.4 eV spectral range withpeak positions at ~2.1 eV and ~1.7 eV accompanied by near-infrared tail. Comparative analysis ofPL spectra of both types’ samples showed that the main contribution to PL spectra of Six(SiO2)1-xfilms is given by exciton recombination in the Si-ncs whereas PL emission of Six(Al2O3)1-x films iscaused mainly by carrier recombination either via defects in matrix or via electron states at the Sincs/matrix interface

Direct bandgap type-I GeSn/GeSn quantum well on a GeSn- and Ge- buffered Si substrate

This paper reports the comprehensive characterization of a Ge0.92Sn0.08/Ge0.86Sn0.14/Ge0.92Sn0.08 single quantum well. By using a strain relaxed Ge0.92Sn0.08 buffer, the direct bandgap Ge0.86Sn0.14 QW was achieved, which is unattainable by using only a Ge buffer. Band structure calculations and optical transition analysis revealed that the quantum well features type-I band alignment. The photoluminescence spectra showed dramatically increased quantum well peak intensity at lower temperature, confirming that the Ge0.86Sn0.14 quantum well is a direct bandgap material

Electron Accumulation Tuning by Surface-to-Volume Scaling of Nanostructured InN Grown on GaN(001) for Narrow-Bandgap Optoelectronics

The existence of an uncontrolled electron accumulation layer near the surface of InN thin films is an obstacle for the development of reliable InN-based devices for use in narrow-bandgap optoelectronics. In this article, we show that this can be regulated by modulating the surface of the InN grown on GaN(001). By increasing the surface-to-volume ratio, we can demonstrate a reduction in the surface carrier concentration from ∼1018 to ∼1017 cm–3. These controlled changes are despite the idea that donor-type surface states, which contribute to conduction band electrons are reported to be the main origin of the surface charge density. Additionally, by evaluating the surface carrier concentration through modeling of photoluminescence (PL) spectroscopy, we have found a failure of the Burstein–Moss theory. Conversely, modeling of the longitudinal optical phonon–plasmon coupled modes measured using Raman spectroscopy, simulations of InN structures using the k·p method, and Hall effect measurements, where possible, showed an excellent correlation of the surface electron concentrations. The large inhomogeneous broadening in the PL, which overwhelms any broadening due to the Burstein–Moss effect, is understood to be the result of varying Stark shifts due to varying strain throughout high surface-to-volume nanostructures, which dramatically affects the spatially indirect nature of the electron–hole recombination. Finally, our findings demonstrate how the electron population of 2D and 3D InN nanostructures can be tuned by structural features, such as porosity and/or the surface-to-volume ratio