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The present work reports the evolution and growth of GeGaAs(O) polytype nanoislands over GaAs p‐type substrate with photoemission application in mind. Several morphological transformations from NIs to simultaneously present nanopits/holes are observed as a function of annealing parameters that is, temperature (350‐800°C) and time (5‐90 minutes). Structural and elemental analyses are executed using atomic force microscopy, scanning electron microscopy and energy dispersive X‐ray spectroscopy. Photoemission current of the nanostructured surfaces, measured upon exposure from 265 nm light emitting diode, is found to depend on the nanoislands size, which in turn depends on the annealing parameters. A maximum photoelectric emission is obtained for structure annealed at 650°C for 60 minutes, upon which an increment of roughly two orders of magnitude is observed.

This study incorporates the structural and magnetic characterization of epitaxial Ni80Fe20 films grown by direct current magnetron sputtering on MgO(001) and MgO(001)||VN(001) substrates. A series of samples grown with different N2 flow settings for the deposition of VN and similar permalloy deposition parameters was utilized to investigate the effect of morphological evolution and buffer layer induced strain on the magnetic properties of Ni80Fe20. X-ray diffraction analysis reveals an epitaxial nature of the VN(001) and Py(001) films grown on MgO substrates. Angular dependent magneto-optical Kerr effect characterization reveals a cubic anisotropy for Ni80Fe20 on MgO with a coercivity of ∼0.8 Gauss along the easy directions. Incorporating an epitaxial VN buffer, the structures showed a transition from a cubic to isotropic magneto-crystalline anisotropy with coercivity varying from 2.5 to 25 Gauss for Ni80Fe20 deposition on VN (with N2 varying from 5 to 12 sccm). The variation is attributed to the microstructural evolution of the Ni80Fe20 to 3D structures along with an induced structural strain., This work was supported by funding from the Icelandic Research Fund Grant Nos. 218029–051, 228951–051 and 207111–051.

Publisher's version (útgefin grein), Films of SiGe nanocrystals (NCs) in oxide have the advantage of tuning the energy band gap by adjusting SiGe NCs composition and size. In this study, SiGe-SiO2 amorphous films were deposited by magnetron sputtering on Si substrate followed by rapid thermal annealing at 700, 800 and 1000 °C. We investigated films with Si:Ge:SiO2 compositions of 25:25:50 vol.% and 5:45:50 vol.%. TEM investigations reveal the major changes in films morphology (SiGe NCs with different sizes and densities) produced by Si:Ge ratio and annealing temperature. XPS also show that the film depth profile of SiGe content is dependent on the annealing temperature. These changes strongly influence electrical and photoconduction properties. Depending on annealing temperature and Si:Ge ratio, photocurrents can be 103 times higher than dark currents. The photocurrent cutoff wavelength obtained on samples with 25:25 vol% SiGe ratio decreases with annealing temperature increase from 1260 nm in SWIR for 700 °C annealed films to 1210 nm for those at 1000 °C. By increasing Ge content in SiGe (5:45 vol%) the cutoff wavelength significantly shifts to 1345 nm (800 °C annealing). By performing measurements at 100 K, the cutoff wavelength extends in SWIR to 1630 nm having high photoresponsivity of 9.35 AW−1., This work was supported by TE Contract no.30/2018 (PN-III-P1-1.1-TE-2016-2050, within PNCDI III), M-ERA.NET PhotoNanoP Contract No. 33/2016, PCE Contract No. 122/2017, PCCDI Contract No. 75/2018, and financed by CNCS-UEFISCDI, and by Romanian Ministry of Research and Innovation through NIMP Core Program PN19-03 (Contract No. 21N/08.02.2019)., "Peer Reviewed"

Silicon nanowires (SiNWs) hold potential applications in optoelectronics and SiNW-based optical sensors. Here, a photoluminescence study of SiNW arrays fabricated with a simple two-step silver (Ag) catalyzed etching of silicon wafers is presented. The morphology and photoluminescence properties were investigated for SiNWs of different lengths obtained by varying Ag concentration (as silver nitrate, AgNO 3 ) and etching time. The samples consist of vertically aligned SiNWs with length in the range ~10-40 µm. Our foremost result is that the photoluminescence intensity from the SiNW arrays is an order of magnitude higher than that from bulk Si. This is accompanied by a red-shift in the peak position of approximately 0.09 eV, which may be attributed either to the variation in size of the Ag-nanoparticles created during the etching process or different lengths of the SiNWs. The results indicate that SiNWs obtained by simple and cost-effective metal catalyzed etching, are potentially promising for optoelectronic applications.

We investigate the formation and evolution of Ga droplets over GaAs (001) substrate with and without Ge top layer (8 nm). Various morphological transformation from holes to droplets formation were observed as a function of annealing parameters. It was observed that the application of Ge layer plays a vital role in incorporating oxygen into the system. Moreover, a potential application of these structures as a photocathode is discussed, demonstrating increased photoemission.

We investigate the structural morphology and electrical characteristics i.e., metal-insulator transition (MIT) of V 2 O 3 thin films grown by high power impulse magnetron sputtering on Al 2 O 3 (c, r, m and a-plane), Si/SiO 2 and Si/ SiO 2 /TiO 2 . The MIT characteristics of films were linked to strain induced by substrate, growth temperature, the O 2 flow settings, the lattice parameters of grown films and the stoichiometry. Of the studied substrates, films grown on c-plane Al 2 O 3 and SiO 2 showed a dominant abrupt transition with a strong MIT. Tunning the electrical transition characteristics of films grown on r-plane reveals MIT characteristics at high growth temperatures at remarkably low O 2 flow settings compared to films grown on c-plane substrates.

We investigate the photoluminescence properties of structures comprising of Si1-xGex nanoparticles (NPs) within SiO2, GeO2, TiO2 and Ta2O5 oxide matrices. Of the investigated structures, it was observed that the structures with GeO2 and TiO2 matrices provide increased spectral response (at ~907 and 844 nm respectively) and increased PL intensity. The improved PL characteristic have been attributed to increased diffusion barrier against oxygen which otherwise would result in formation of unwanted oxide at the film-oxide interface, thereby deteriorating the optical properties., This work is partially funded by the Icelandic Research Fund Grants nos. 218029 and 196141., Pre-print (óritrýnt handrit)

Publisher's version (útgefin grein), Multilayer structures comprising of SiO2/SiGe/SiO2 and containing SiGe nanoparticles were obtained by depositing SiO2 layers using reactive direct current magnetron sputtering (dcMS), whereas, Si and Ge were co-sputtered using dcMS and high-power impulse magnetron sputtering (HiPIMS). The as-grown structures subsequently underwent rapid thermal annealing (550-900 degrees C for 1 min) in N-2 ambient atmosphere. The structures were investigated using X-ray diffraction, high-resolution transmission electron microscopy together with spectral photocurrent measurements, to explore structural changes and corresponding properties. It is observed that the employment of HiPIMS facilitates the formation of SiGe nanoparticles (2.1 +/- 0.8 nm) in the as-grown structure, and that presence of such nanoparticles acts as a seed for heterogeneous nucleation, which upon annealing results in the periodically arranged columnar self-assembly of SiGe core-shell nanocrystals. An increase in photocurrent intensity by more than an order of magnitude was achieved by annealing. Furthermore, a detailed discussion is provided on strain development within the structures, the consequential interface characteristics and its effect on the photocurrent spectra., M-ERA. NET project PhotoNanoP UEFISCDI Contract no. 33/2016, PCE project UEFISCDI Contract no. 122/2017 and by Romanian Ministry of Research and Innovation through NIMP Core Program PN19-03, contract no. 21 N/08.02.2019 and by the Technology Development Fund of the Icelandic Centre for Research, grant no. 159006-0611., "Peer Reviewed"

We investigate the effect of room-temperature hydrogen-plasma treatment on the photoconductivity of SiGe nanoparticles sandwiched within SiO2 layers. An increase in photocurrent intensity of more than an order magnitude is observed after the hydrogen plasma treatment. The enhancement is attributed to neutralization of dangling bonds at the nanoparticles and to passivation of nonradiative defects in the oxide matrix and at SiGe/matrix interfaces. We find that increasing the partial pressure of hydrogen to pressures where H3+ and H2+ were the dominant ions results in increased photocurrent.

Photosensitive films based on finely dispersed semiconductor nanocrystals (NCs) in dielectric films have great potential for sensor applications. Here we report on preparation and characterization ...

We investigate the effect of hydrogen plasma treatment on the metal-insulator transition (MIT) of epitaxial V2O3 films grown on c-Al2O3. The films were exposed to plasma at constant power for varying intervals. With increasing hydrogenation the films display a suppression of the MIT magnitude and temperature due to neutralization of structural defects and passivation of unpaired bonds by incorporation of atomic hydrogen as supported by relaxation in strain by XRD and Raman spectroscopy analysis, while stabilizing the metallic phase due to reduction in Peierls dimerization of V-V bonds. Heating to 350-400 °C the electrical characteristics of the film in the as-grown state are regained showing the possibility of reversibly controlling the MIT characteristics.

Hydrogenation is a widely used method to improve performance of electronic devices made from silicon but much less frequently to improve corresponding optical properties. Here, we study the possible use of hydrogenation to reduce inherent optical loss in silicon. We address enablement of efficient resonance metastructures such as filters, wideband reflectors, and polarizers via successful outcomes of such experimentation. A noticeable reduction in attenuation is observed.

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

The study presents the dynamics of solid-state dewetting of silver (Ag)-film annealed in N2 ambient, analyzed by atomic force microscopy and scanning electron microscopy. Varying the annealing parameters (i.e. temperature and time) and Ag-film thicknesses were taken into account, to determine their effect over the solid-state dewetting of Ag-films. Several morphological evolutions from nanohole to the presence of metastable nanorings were observed. It was determined that structures annealed at high temperature (≥900 °C) and/or time (≥2 h) results in formation of metastable nanorings and whose geometrical aspects and population grew with increasing film thickness. Possible applications of the structures for fabrication of silicon nanowire arrays and photo-emitters are briefly described.

We study the surface morphology and growth process of SiGe nanoislands on TiO2 films, deposited over Si (001) substrates by high power impulse magnetron sputtering, followed by varying annealing parameters (i.e., 500–750 °C for 30 min to 20 h). Structural analysis was performed by atomic force microscopy, scanning electron microscopy, and grazing incidence x-ray diffraction. Two structural schemes were taken into consideration, i.e., SiGe grown over pre-annealed TiO2 (scheme I) and as-grown TiO2 (scheme II). Photoluminescence (PL) study of the structures revealed spectral features comprised of multiple peak features related to localized and surface states within the oxide layer, along with a peak due to the SiGe nano-islands. It was observed that the spectral feature and intensity depend on the surface morphology and the crystallinity of the underlying TiO2 layer. The structures were subjected to low temperature PL measurements, and the spectra were de-convoluted in order to validate the origin of the obtained spectra. Structural analysis revealed that pre-annealing the underlying polycrystalline TiO2 film, prior to deposition of SiGe layers (scheme I), facilitates the formation of SiGe nanoislands, preferably along the grain boundaries (due to their higher interfacial energy). In comparison, for the case of SiGe deposited over as-grown TiO2 (scheme II), annealing of the structure resulted in random distribution of nanoislands across the entire film. The size of the nanoislands grew with increased annealing time up until the point they started to coalesce, forming discontinuous SiGe layers and eventually leading to melting of the layer.

Formation of SiGe nanocrystals in an oxide matrix via deposition and subsequent annealing is a widely applied approach as it gives good control over optical properties by varying the Ge atomic fraction, the size, shape and crystallinity of the nanocrystals. A common drawback of annealing is a strain relaxation in the structure creating dislocations, point defects, dangling bonds, Ge clustering and altered interface morphology. All these phenomena are well-known to degrade the optoelectronic and electrical properties of the structure. As a proof of concept, in this study we have utilized a modern technique of high impulse power magnetron sputtering (HiPIMS) to obtain a crystalline TiO2/SiGe/TiO2 structure without any pre-/post-annealing. It is furthermore demonstrated how a control of the nano-crystallite size is obtained by altering the HiPIMS discharge power alone. Grazing incidence X-ray diffraction analysis was carried out for the structural characterization, while photocurrent measurements were utilized to access the role of TiO2 structural morphology over interface integrity in determining spectral feature and sensitivity. An increase of 1 – 2 orders magnitude in spectral intensity was achieved for as-grown structures fabricated via HiPIMS in comparison to annealed structure, sputtered with conventional direct current magnetron sputtering.

The effect of room temperature hydrogen plasma treatment on the photoconductive properties of the SiO 2 matrix containing SiGe nanoparticles is investigated. A considerable increase in photocurrent intensity is observed after plasma treatment. The increase is partly attributed to neutralization of dangling bonds around the nanoparticles and partly to passivation of non-radiative centers and defects in the matrix and at the nanoparticles-matrix interfaces.

GeSi NCs / Ti0 2 multilayers with enhanced photocurrent properties were prepared and studied. Multilayers of Ti0 2 /(GeSi/Ti0 2 )x2 /Si-p were deposited by magnetron sputtering and annealed by RTA at 700 °C for GeSi NCs formation. A post-annealing hydrogenation in plasma was performed on multilayers for healing of defects acting as traps and/or recombination centers and consequently producing the photocurrent enhancement. We studied the electrical and photoconductive properties of multilayers annealed by RTA and post-annealing hydrogenated. The current - temperature dependence reveals the conduction mechanisms in GeSi NCs / Ti0 2 multilayers RTA annealed, i.e. thermal activation of carriers to extended states (0.31 eV activation energy), the electron tunneling mechanism to nearest neighbors (T-1/2 behavior) and Mott variable range hopping (T−1/4 dependence). The photocurrent spectra made on multilayers structures hydrogenated for 10, 20 and 30 min evidence the photocurrent increasing up to 50%, showing that the hydrogenation is a suitable treatment for enhancing photocurrent. All photocurrent spectra present a dominant maximum (920 nm) and two shoulders (~770 and~ 10 60 nm).

We studied the effect of short term furnace annealing over the photoconductive properties of tristacked layer i.e. TiO2/(SiGe/TiO2)3. The structure was prepared by depositing alternate layers of TiO2 and SiGe films, using direct-current magnetron sputtering technique. A transmission electron microscopy and grazing incidence spectroscopy was used to analyze the morphology of the structure. Photoconductive properties were studied by measuring photocurrent spectra at different applied voltages and temperatures. Tristack layers were obtained with 5–10 nm SiGe nanocrystals (NCs) by annealing at 600 °C for 5 min. No sign of SiO2 formation was found inside stacked layers. A maximum in the photocurrent spectra was observed at 994 nm at 300 K but it red-shifted gradually to 1045 nm with decrease in temperature to 100 K. This transition in peak maxima is attributed to SiGe NCs, due to lattice vibration and to contribution of non-radiative recombination at low temperatures.

The photosensing properties related to the structure of GeSi/TiO2 multilayers prepared under different conditions are studied. TiO 2 cap/(GeSi/TiO 2 ) 2 multilayers (ML) were deposited by magnetron sputtering (MS) and annealed by rapid thermal annealing. Trilayers of TiO 2 cap/GeSi/TiO 2 (TL) were also deposited using reactive high power impulse MS (HiPIMS) for TiO 2 layers and dc MS for the GeSi layer. For TL samples a two-step annealing was employed, one before and the second after depositing TiO 2 cap. Structure and morphology characterization (X-ray diffraction, scanning and transmission electron microscopy) was carried out and photocurrent measurements (voltage dependences, spectral curves) were performed. The annealed ML samples are formed of GeSi NCs with 5–10 nm sizes, while in the annealed TL samples, the GeSi NCs are larger (20–30 nm). These morphologies determine the multilayers photosensing properties in VIS-NIR of ML structures and in UV in TL ones, respectively.