arXiv subjects

F. B. Naranjo

Publications and source records attributed to F. B. Naranjo.

9 recordsLinked to original sources

arXiv2025

Enhancing solar cell efficiency of AlxIn1-xN/Si heterojunctions using an a-Si buffer: A study of material, interface and device properties

This study explores the impact of an optimized amorphous silicon (a-Si) buffer layer on AlxIn1-xN-on-Si(100) heterojunction solar cells, with Al content varying from 0% (InN) to 55%. The buffer layer improves the structural quality of the AlInN layer, as evidenced by reduced full width at half maximum values in X-ray diffraction rocking curves around the AlInN (0002) peak. Atomic force microscopy reveals that the buffer layer does not alter surface roughness. The effectiveness of the a-Si buffer is demonstrated by an enhancement of the conversion efficiency under AM1.5G illumination from 3.3 % to 3.9 % for devices with 35 % Al. Looking at the effect of the Al content in devices with the a-Si buffer, the device with 22% Al shows the best photovoltaic performance, with a conversion efficiency of 4.1 % and a VOC of 0.42 V, JSC of 15.4 mA/cm2, and FF of 63.3%. However, performance declines for Al contents above 36% due to increased resistivity and reduced carrier concentration. These findings highlight the critical role of the novel a-Si buffer layer developed by RF-sputtering and the Al content in optimizing AlInN/Si heterojunction solar cell performance.

cond-mat.mtrl-sci↗

arXiv2025

Low-to-mid Al content ($x\sim$ 0-0.56) Al$_x$In$_{1-x}$N layers deposited on Si(100) by radio-frequency sputtering

Radio-frequency (RF) sputtering is a low-cost technique for the deposition of large-area single-phase AlInN on silicon layers with application in photovoltaic devices. Here, the effect of the Al mole fraction x from 0 to 0.56 on the structural, morphological, electrical, and optical properties of $n$ Al$_x$In$_{1-x}$N layers deposited at 550 $^\circ$C on p-Si(100) by RF sputtering is studied. X-ray diffraction data show a wurtzite structure oriented along the c-axis in all samples, where the full width at half maximum of the rocking curve around the InN (0002) diffraction peak decreases from $\sim 9^\circ$ to $\sim 3^\circ$ while incorporating Al to the AlInN layer. The rootmean-square surface roughness, estimated from atomic force microscopy, evolves from 20 nm for InN to 1.5 nm for Al$_{0.56}$In$_{0.44}$N. Low-temperature photoluminescence spectra show a blueshift of the emission energy from 1.59 eV (779 nm) for InN to 1.82 eV (681 nm) for Al$_{0.35}$In$_{0.65}$N according to the Al content rise. Hall effect measurements of Al$_x$In$_{1-x}$N ($0<x <0.35$) on sapphire samples grown simultaneously point to a residual n-type carrier concentration in the 1021 cm$^{-3}$ range. The developed n-AlInN/p-Si junctions present promising material properties to explore their performance operating as solar cell devices.

cond-mat.mtrl-sci↗

arXiv2025

Effect of temperature and excitation power on down-conversion process in Tb3+/Yb3+-activated silica-hafnia glass-ceramic films

Transparent glass ceramics, when activated by rare earth ions, are excellent photonic materials. Regarding photonic glass-ceramics based on silicates, hafnia and silica in a binary system has proved to be an excellent matrix to incorporate rare earth ions in the hafnia nanocrystals, resulting in important luminescence enhancement and, consequently, allowing a large spectrum of critical applications. Here we will focus on the downconversion mechanism driven by the couple Tb3+/Yb3+, largely exploited in photovoltaic systems. The research presented here has been performed on 70SiO2-30HfO2 silica-hafnia glass-ceramic films activated with 19 % rare earth ions: [Tb + Yb]/[Si + Hf] = 19 %. Two main results will be discussed: (a) the intensity and the broadening of the Yb3+ emission band at 975 nm were found to be temperature-dependent, as shown in the figure; (b) the energy transfer mechanism Tb3+ >> Yb3+ will be discussed, referring to the mechanisms that have been proposed in the literature. In relation to the latter topic, the power dependence spectra for the luminescence of Yb3+: 2F5/2 >> 2F7/2 will be discussed.

cond-mat.mtrl-sci↗

arXiv2025

InN nanowire solar cells on Si with amorphous Si interlayer deposited by sputtering

Here, we report the first experimental demonstration of InN nanowire solar cells deposited by RF sputtering with a bandgap energy of 1.78 eV. By adding an amorphous Si (a-Si) buffer to the n-InN/p-Si structure, we have improved the photovoltaic performance of the resulting devices while maintaining their material quality. We have firstly optimized the deposition of Si on Si(100) by DC sputtering, obtaining an amorphous material with bandgap energy of 1.39 eV. Then we have studied the influence of the thickness of the a-Si buffer layer (0-25 nm) on the structural, morphological, electrical, and optical properties of InN nanowires on Si (100) substrates. With the use of a 15-nm buffer, n-InN/a-Si/p-Si nanowire heterojunction solar cells exhibit a promising short-circuit current density of 17 mA/cm2, open circuit voltage of 0.37 V and fill factor of 35.5%, pointing to a power-conversion efficiency of 2.3% under 1-sun (AM 1.5G) illumination. These work demonstrated that the combination of in-situ sputtered a-Si, which could serve as potential passivation layer, and the light trapping enhancement by the nanostructured active layer leads to an improvement of the photovoltaic efficiency of sputtered III-nitride devices.

physics.app-ph↗

arXiv2021

Comparison of the material quality of AlxIn1-xN (x ~ 0-0.50) films deposited on Si (100) and (111) by reactive RF sputtering

Here, we compare the material quality of AlxIn1-xN layers deposited on Si with different crystallographic orientations, (100) and (111), via radio-frequency (RF) sputtering. To modulate their Al content, the Al RF power was varied from 0 to 225 W, whereas the In RF power and deposition temperature were fixed at 30 W and 300oC, respectively. X-ray diffraction measurements reveal a c-axis-oriented wurtzite structure with no phase separation regardless of the Al content (x = 0-0.50), which increases with the Al power supply. The surface morphology of the AlxIn1-xN layers improves with increasing Al content and it is similar for samples grown on both Si substrates (the root-mean-square roughness decreases from 12 nm to 2.5 nm). Furthermore, from TEM images we notice a similar grain-like columnar morphology and defect density on samples deposited on both Si substrates under the same conditions. Simultaneously grown AlxIn1-xN-on-sapphire samples point to a residual n-type carrier concentration in the 1020-1021 cm-3 range. The optical band gap energy of these layers evolves from 1.75 eV to 2.56 eV with increasing Al content, consistent with the blue shift of their low-temperature photoluminescence. In general, the material quality of the AlxIn1-xN films on Si is similar for both crystallographic orientations. Nonetheless, samples deposited on sapphire show an improved structural and morphological characteristic likely due to the lower difference in lattice constants between the nitride and the sapphire substrate.

cond-mat.mtrl-sci↗

arXiv2019

Design of n-AlInN on p-silicon heterojunction solar cells

Aluminum Indium Nitride (AlInN) alloys offer great potential for photovoltaic devices thanks to their wide direct bandgap energy that covers the solar spectrum from 0.7 eV (InN) to 6.2 eV (AlN), and their superior resistance to high temperatures and high-energy particles. In this paper, we report the design of AlInN on silicon heterojunctions, with the aim to explore their potential for solar cell devices through the analysis and optimization of the properties of the AlInN on Si heterojunction. In particular, we study the influence of the AlInN bandgap energy, AlInN thickness and carrier concentration, silicon surface recombination, interface defects and Si wafer quality on the photovoltaic properties (conversion efficiency and external quantum efficiency) of the AlInN on Si heterojunctions. The effect of introducing an anti-reflective coating is also studied. Optimized AlInN on Si heterostructure shows a conversion efficiency of 18% under 1-sun AM1.5G illumination for low-quality Si wafers, which increases to 23.6% for high-quality Si wafers and incorporating a properly designed anti-reflective layer. In comparison with standard Si solar cells without AlInN, the external quantum efficient of the devices increases for wavelengths below 500 nm, making them appealing for space applications. These results lead to the AlInN on Si heterojunction a promising future as a novel technology for solar cell devices.

physics.app-ph↗

arXiv2019

High quality Al$_{0.37}$In$_{0.63}$N layers grown at low temperature (<300$^\circ$C) by radio-frequency sputtering

High-quality Al0.37In0.63N layers have been grown by reactive radio-frequency (RF) sputtering on sapphire, glass and Si (111) at low substrate temperature (from room temperature to 300°C). Their structural, chemical and optical properties are investigated as a function of the growth temperature and type of substrate. X-ray diffraction measurements reveal that all samples have a wurtzite crystallographic structure oriented with the c-axis perpendicular to the substrate surface, without parasitic orientations. The layers preserve their Al content at 37 % for the whole range of studied growth temperature. The samples grown at low temperatures (RT and 100°C) are almost fully relaxed, showing a closely-packed columnar-like morphology with an RMS surface roughness below 3 nm. The optical band gap energy estimated for layers grown at RT and 100°C on sapphire and glass substrates is of ~2.4 eV while it red shifts to ~2.03 eV at 300°C. The feasibility of growing high crystalline quality AlInN at low growth temperature even on amorphous substrates open new application fields for this material like surface plasmon resonance sensors developed directly on optical fibers and other applications where temperature is a handicap and the material cannot be heated.

physics.app-ph↗

arXiv2019

Effect of different buffer layers on the quality of InGaN layers grown on Si

This work studies the effect of four different types of buffer layers on the structural and optical properties of InGaN layers grown on Si(111) substrates and their correlation with electrical characteristics. The vertical electrical conduction of n-InGaN/buffer-layer/p-Si heterostructures, with In composition near 46%, which theoretically produces an alignment of the bands, is analyzed. Droplet elimination by radical-beam irradiation was successfully applied to grow high quality InGaN films on Si substrates for the first time. Among several buffer choices, an AlN buffer layer with a thickness above 24 nm improves the structural and optical quality of the InGaN epilayer while keeping a top to bottom ohmic behavior. These results will allow fabricating double-junction InGaN/Si solar cells without the need of tunnel junctions between the two sub-cells, therefore simplifying the device design.

physics.app-ph↗

arXiv2018

Influence of the AlN interlayer thickness on the photovoltaic properties of In-rich AlInN on Si heterojunctions deposited by RF sputtering

We report the influence of the AlN interlayer thickness (0-15 nm) on the photovoltaic properties of Al0.37In0.63N on Si heterojunction solar cells deposited by radio frequency sputtering. The poor junction band alignment and the presence of a 2-3 nm thick amorphous layer at the interface mitigates the response in devices fabricated by direct deposition of n-AlInN on p-Si(111). Adding a 4-nm-thick AlN buffer layer improves the AlInN crystalline quality and the interface alignment leading to devices with a conversion efficiency of 1.5% under 1-sun AM1.5G illumination. For thicker buffers the performance lessens due to inefficient tunnel transport through the AlN. These results demonstrate the feasibility of using In-rich AlInN alloys deposited by radio frequency sputtering as novel electron-selective contacts to Si-heterojunction solar cells.

physics.app-ph↗