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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.

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 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 ...

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.

Circular economy solutions reuse and upcycle waste streams in order to minimize the use of resources and mitigate the creation of waste and emissions. Accordingly, circular economy solutions are an essential tool to tackle the imminent challenges of depleting resources and the emerging environmental crisis. In this presentation, we explore the circular solutions for resource recovery in waste streams in a country with one of the highest Gross Domestic Product (GDP) and Human Development Index (HDI) in Europe, Iceland. The economy of Iceland is mainly based on renewable energy, fishery, farming, metallurgy, and tourism. To assess the benefits of circular economy solutions we examine four relevant case studies from the following industrial sectors in Iceland: i) a geothermal energy plant, ii) fisheries, iii) domestic waste processing and iv) aluminium production. By describing the processes, the opportunities and the market potential of the circular economy solutions in the four case studies we identify the superiority of circular recovery of resources in a modern society. The results reveal that the recovery of resources reduces the environmental impacts, increases the economic output and enhances the resilience of the local economy. While our results are based on the examples in Iceland the described processes of resource recovery can be applied in any other country with similar resources. We conclude that the presented circular solutions could lead to a more sustainable world while preserving vital resources for the next generations.

The Blue Lagoon is a geothermal aquifer with a diverse ecosystem located within the Reykjanes UNESCO Global Geopark on Iceland's Reykjanes Peninsula. Blue Lagoon Ltd., which exploits the aquifer, isolated a strain of coccoid cyanobacteria Cyanobacterium aponinum (C. aponinum) from the geothermal fluid of the Blue Lagoon more than two decades ago. Since then Blue Lagoon Ltd. has cultivated it in a photobioreactor, for use as an active ingredient in its skin care products. Until recently, the cultivation of C. aponinum was achieved by feeding it on 99.99% (4N) bottled carbon dioxide (CO2). In this investigation, C. aponinum was cultivated using unmodified, non-condensable geothermal gas (geogas) emitted from a nearby geothermal powerplant as the feed-gas instead of the 4N-gas. The geogas contains roughly 90% vol CO2 and 2% vol hydrogen sulfide (H2S). A comparison of both CO2 sources was made. It was observed that the use of geogas did enhance the conversion efficiency. A 13 weeks' average CO2 conversion efficiency of C. aponinum was 43% and 31% when fed on geogas and 4N-gas, respectively. Despite the high H2S concentration in the geogas, sulfur accumulation in the cultivated biomass was similar for both gas sources. Our results provide a model of a CO2 sequestration by photosynthetic conversion of otherwise unused geothermal emission gas into biomass.

We monitored the evolution in time of pinhole-free structures based on FTO/TiO2/CH3NH3PbI2.6Cl0.4 layers, with and without spiro-OMeTAD and counter electrodes (Ag, Mo/Ag, and Au), aged at 24 °C in a dark nitrogen atmosphere. In the absence of electrodes, no degradation occurs. While devices with Au show only a 10% drop in power conversion efficiency, remaining stable after a further overheating at 70 °C, >90% is lost when using Ag, with the process being slower for Mo/Ag. We demonstrate that iodine is dislocated by the electric field between the electrodes, and this is an intrinsic cause for electromigration of I– from the perovskite until it reaches the anode. The iodine exhaustion in the perovskite layer is produced when using Ag electrodes, and AgI is formed. We hypothesize that in the presence of Au the iodine migration is limited due to the buildup of I– negative space charge accumulated at the perovskite–OMeTAD interface.

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

Publisher's version.(útgefin grein), Fabrication and sensor application of a simple plasmonic structure is described in this paper. The sensor element consists of nano-patterned gold film brought about from two-dimensional periodic photoresist templates created by holographic laser interference lithography. Reflectance spectroscopy revealed that the sensor exhibits significant refractive index sensitivity. A linear relationship between shifts in plasmonic resonances and changes in the refractive index were demonstrated. The sensor has a bulk sensitivity (SB) of 880 nm/refractive index unit and work under normal incidence conditions. This sensitivity exceeded that of many common types of plasmonic sensors with more intricate structures. A modeled spectral response was used to study the effect of its geometrical dimensions on plasmonic behavior. A qualitative agreement between the experimental spectra and modeled ones was obtained., This research was supported in part by the UT System Texas Nanoelectronics Research Superiority Award funded by the State of Texas Emerging Technology Fund. Additional support was provided by the Texas Instruments Distinguished University Chair in Nanoelectronics endowment., "Peer Reviewed"

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.

Silica, precipitated out of geothermal fluid discharged from a geothermal powerplant in Svartsengi on the Reykjanes peninsula in Iceland, was used as a chromatographic adsorbent to extract blue colored protein, C-phycocyanin, from coccoid blue-green algae. The only supplement used was salt obtained by evaporating the geothermal fluid. Analysis of the silica, using scanning electron microscopy, X-ray diffractometry and Brunauer–Emmett–Teller (BET) adsorption confirmed it has a high specific surface area and is amorphous. Upon adsorption and subsequent elution the purity of the extracted protein, measured as the ratio of the light absorbance of 620 and 280 nm, increased from 0.5 to above 2.0. Our results could facilitate utilization of a mostly unused byproduct of geothermal powerplants as chromatographic material.

We review nanophotonic device technology that is based on fundamental photonic resonance effects. We present the physics behind resonance device operation, illustrate their design with rigorous methods, discuss fabrication processes, and present results of physical and spectral characterization. We indicate the application potential of this field, discuss some past device examples, and provide new and emerging aspects. In particular, we present new wideband resonant reflectors designed with gratings in which the grating ridges are matched to an identical material thereby eliminating local reflections and phase changes. This critical interface therefore possesses zero refractive-index contrast; hence we call them “zero-contrast gratings.” For simple gratings with two-part periods, we show that zero-contrast grating reflectors outperform comparable high-contrast grating reflectors with nearly 700-nm bandwidth achieved at 99% reflectance. Resonance elements functioning as simultaneous spatial and spectral filters are introduced and substantiated with computed and experimental results that are in excellent agreement. Single-layer bandpass filters are presented and compared to their classic multilayer counterparts. An example bandpass filter with narrow transmission band fashioned with a single periodic layer compares in functionality with a classic Bragg stack with ∼30 layers. We discuss deep Si grating structures that efficiently absorb fully-hemispherical unpolarized light in the entire visible spectral domain. This absorber provides a broad spectral continuum of densely populated resonant photonic states as well as a cooperating wide-angular antireflection effect, resulting in broadband, omnidirectional, and polarization-insensitive light absorption. We experimentally verify the absorber performance with precise fabrication and conical input beam spectral analysis. The promise and limitations of this class of devices is discussed.

Metal-catalysed etching (MCE) is a simple and versatile method for fabrication of silicon nanowires, of high structural quality. When combined with laser interference lithography (LIL), large areas of periodic structures can be generated in only few steps. The aspect ratio of such periodic structure is however commonly not higher than several decades or very few hundred. Here, a combined MCE and LIL techniques were applied to fabricate dense (4 × 108 cm−3), periodic arrays of vertically aligned silicon nanowires with aspect ratio of up to 103. This is a considerable higher number than previously reported on for periodic silicon wire arrays prepared with top–down approaches. The wires were slightly tapered, with top and bottom diameters ranging from 370 to 195 nm and length of up to 200 μm. A potential use of the nanowires as light absorber is demonstrated by measuring reflection in integrating sphere. An average total absorption of ~97 % was observed for 200-μm-long wires in the spectral range of 450–1000 nm. A comparison to simulated absorption spectra is given.

Fabrication of plasmonic resonance devices composed of large arrays of highly ordered gold nanocups is presented. The nanostructures are generated from periodic photoresist templates created by interference lithography and subsequent reflow, deposition, and dislodging. The nanocups are hemispherical in shape and arranged in both rectangular and hexagonal arrays with periods of ~500 nm. Their ability to support surface plasmonic resonances is manifested experimentally by reflectance spectroscopy. Theoretical modeling to ascertain the plasmonic spectra of these nanostructures is performed. The computed spectra of the rectangular structure are in qualitative agreement with the measurements. A weaker correlation observed for the hexagonal structure is explained by its more intricate symmetry which complicates the spectral response.

A facile procedure to fabricate large arrays of highly ordered metal nanocups, 250 nm in diameter, is reported. The nanostructure is generated from periodic photoresist templates created by holographic laser interference lithography. A subsequent gold deposition and a peeling-off step respectively results in a large area of hemispherical nano-indentations or nanocups. A wide range of coating materials can be used, and the dimensions and periodicity of the structure are easily controlled. The structure’s ability to support localized surface plasmon polaritons was manifested by reflectance spectroscopy. A good correlation between experimental data and calculated data was observed.

We report on measurements of the frequency-dependent conductivity in lithium-diffused (Li-diffused) and annealed GaAs in the frequency range 10– 10 6 Hz and the temperature range 30– 300 K . Li diffusion into GaAs reduces the free carrier concentration and can make the material semi-insulating. Using admittance spectroscopy we show that the conduction in semi-insulating Li-diffused GaAs is due to hopping between localized centers. These centers are suggested to be associated with the gallium vacancy VGa and the gallium antisite GaAs. Furthermore, percolation is apparent in as-diffused samples, indicating that the material contains metallic precipitates. We suggest that the percolation is due to Li precipitation or formation of GaLi clusters during in-diffusion of lithium. At high frequency the AC conductivity is proportional to ωs. The value of s decreases with increasing temperature which suggests a correlated barrier hopping mechanism.

Si-doped GaAs layers were grown p-type at 700°C and n-type at 840°C by liquid phase epitaxy. Thermal annealing of the p-type samples at temperatures around 840°C converted the samples to n-type. We compare the as-grown and annealed samples by means of photoluminescence and temperature-dependent Hall and conductivity measurements. Highly doped samples converted to n-type through annealing become highly compensated. Their Hall mobility also increases more than an order of magnitude. Samples grown n-type at 840°C show up to three times higher mobility than the annealed ones. The compensation in each case was monitored through the shift of the photoluminescence bands with excitation intensity, up to 24 meV per decade of increase in the excitation power density for the highest compensation ratio.

Electrostatic powder impact deposition (EPID) is a novel method to deposit thin films by electrostatic acceleration of powder material between charged plates in vacuum. The EPID method has been used to deposit Ge films on Si and Cu substrates at room temperature. Surface morphology and microstructure as studied by SEM showed a very rough surface. XRD and RBS measurements revealed that the films were mostly nanocrystalline or amorphous Ge oxide. The grain size distribution of the Ge powder was measured before and after deposition. Initial distribution showed a median grain size of 32??m and distribution width of 80??m. After the deposition the median grain size had decreased to 16??m and the width decreased to 55??m. The grain size of the deposited film was less than 1??m.

We study the effect of hydrogen passivation on Al x Ga 1− x As grown by liquid-phase epitaxy (LPE) on semi-insulating GaAs. Using surface photovoltage (SPV) spectroscopy and Hall measurements we investigate the effect of hydrogenation on Al x Ga 1− x As epilayers with electron concentrations in the range 10 16 –10 17 cm −3 . We measure the minority carrier diffusion length in the as-grown Al x Ga 1− x As epilayers to be in the range 0.1–0.8 μm and to increase significantly upon hydrogenation. Hydrogen passivation of interface states at the heterojunction is demonstrated for epilayers with low carrier concentration. We apply the result from the SPV measurements to speculate on the band bending at the heterojunction.

Using Hall and conductivity measurements the formation of a Li–Au-related complex in p-type crystalline silicon is demonstrated. Substitutional gold is known to introduce two energy levels in the band gap of silicon, a deep acceptor level at Ec−0.56 eV and a deep donor level at Ev+0.34 eV. We observe two energy levels introduced by lithium diffusion of Au-doped silicon, a previously reported acceptor at Ec−0.41 eV in n-type Si : Au and a new level at Ev+0.41 eV in p-type Si : Au. In addition, control of the Li-doping level of p-type Si is found to shift the Fermi level position between the deep donor level to the deep acceptor level as expected, thus confirming their presence in the samples. We discuss the identity of these levels in comparison with theoretical predictions for the interaction between hydrogen and the energy levels of substitutional Au in silicon.

An expedient procedure to fabricate large arrays of highly ordered metal nanocups, 150-200 nm in diameter, is reported. Their ability to support localized surface-plasmon polaritons is manifested by reflectance spectroscopy.

We study lithium-diffused and annealed GaAs by admittance spectroscopy in the frequency range $10\char21{}{10}^{6}\mathrm{Hz}$ and the temperature range 30\char21{}300 K. Li diffusion turns the GaAs semi-insulating but subsequent out-diffusion of Li increases the conductivity and makes the samples p type. It is demonstrated that the conduction in semi-insulating Li-diffused GaAs is due to thermally activated carriers in the valence-band percolating around insulating metallic precipitates. At high frequencies the ac conductivity is proportional to ${\ensuremath{\omega}}^{x},$ with x being close to unity value, independent of temperature. We suggest that the percolation may be due to metallic precipitates formed during in-diffusion of lithium and following cooling. After subsequent annealing the ac conductivity becomes proportional to ${\ensuremath{\omega}}^{s}$ at high frequencies with the value of s decreasing with increasing temperature. The temperature dependency of s suggests a correlated barrier hopping mechanism in a band of defects. We attribute these defects to gallium vacancies ${V}_{\mathrm{Ga}}$ and gallium antisites ${\mathrm{Ga}}_{\mathrm{As}}.$

Temperature dependent conductivity and Hall effect measurements were carried out in the temperature range 30-300 K on Li-diffused and annealed GaAs. Li in-diffusion into GaAs reduces the free carrier concentration which leads to electrical conductivity as low as 10/sup -7/ S/cm. Annealing the lithium diffused samples at temperatures above 200/spl deg/C significantly increases the room temperature conductivity to 1-10 S/cm, depending on the annealing temperature. In samples annealed at 300-500/spl deg/C the temperature dependence of the conductivity indicates that hopping conduction sets in at temperatures below 100 K. We relate this to enhanced gallium vacancy (V/sub Ga/) and gallium antisite (Ga/sub As/) concentration in Li in-diffused and annealed samples.

Originally n-type Si-doped GaAs turns p-type after Li indiffusion and consequent annealing at 200-600°C. Temperature-dependent conductivity and Hall effect measurements carried out in the temperature range 30-300 K revealconduction via impurity bands made up of shallow acceptors in addition to the valence-band conduction. Li diffusion into GaAs reduces the free-carrier concentration which leads to electrical resistivity as high as 10 7 Ω cm. Annealing highly resistive samples at temperatures above 200 °C significantly decreases the room-temperature resistivity to 0,1-1 Ω cm, depending on the annealing temperature. For samples annealed at 300-400°C we observe a metallic-type conduction which contributes to the conduction even at room temperature. In samples annealed at 500-600 °C the temperature dependence of the resistivity indicates that impurity conduction sets in at temperatures below 100 K. We discuss this conduction change in relation to enhanced gallium vacancy (V G a ) and gallium antisite (Ga A s ) concentration in Li indiffused and annealed samples.

A single-step, low-cost fabrication method to generate resonant nano-grating patterns on poly-methyl-methacrylate (PMMA; plexiglas) substrates using thermal nano-imprint lithography is reported. A guided-mode resonant structure is obtained by subsequent deposition of thin films of transparent conductive oxide and amorphous silicon on the imprinted area. Referenced to equivalent planar structures, around 25% and 45% integrated optical absorbance enhancement is observed over the 450-nm to 900-nm wavelength range in one- and two-dimensional patterned samples, respectively. The fabricated elements provided have 300-nm periods. Thermally imprinted thermoplastic substrates hold potential for low-cost fabrication of nano-patterned thin-film solar cells for efficient light management.

We provide experimental evidence of a hybrid photonic device supporting simultaneously surface-plasmon polaritons and resonant leaky modes. A fabricated metallo-dielectric structure exhibits a pronounced plasmonic resonance at 799 nm wavelength and a modal resonance at 669 nm in transverse magnetic polarization. In transverse electric polarization, a weak modal resonance appears at 725 nm wavelength. We identify the corresponding modes by computing the attendant internal field distributions. Numerically computed spectra are in good agreement with our measurements. Since traditional modal and plasmonic devices find many uses, their hybrid versions may enable the extension of their applicability.

Silicon p–n junctions for solar cell applications were prepared by growing thin n-type films on p-type metallurgical-grade silicon (MG-Si) substrate in a liquid solution of arsenic-doped gallium/indium solution. MG-Si has much higher impurity concentrations than traditional solar-grade silicon, but is here being used as a low-cost alternative. The as-grown film showed negligible photovoltaic response. A post-growth exposure of the as-grown p–n junctions to a H2/Ar plasma resulted in an active photovoltaic device with VOC of up to several hundred mV. Furthermore, a significant increase in the minority carrier lifetime was observed. The short-circuit current density indicated low efficiency in accordance with the high defect concentration of the impure substrate. An x-ray diffraction study of MG-Si prior to and after film growth revealed textured crystal structure that diminished during film growth, indicating that the film is more homogeneous than the substrate.