AlxIn1−xN on Si (100) Solar Cells (x = 0–0.56) Deposited by RF Sputtering

We investigate the photovoltaic performance of solar cells based on n-AlxIn1−xN (x = 0–0.56) on p-Si (100) hetero-junctions deposited by radio frequency sputtering. The AlxIn1−xN layers own an optical bandgap absorption edge tuneable from 1.73 eV to 2.56 eV within the Al content range. This increase of Al content results in more resistive layers (≈10−4–1 Ω·cm) while the residual carrier concentration drops from ~1021 to ~1019 cm−3 . As a result, the top n-contact resistance varies from ≈10−1 to 1 MΩ for InN to Al0.56In0.44N-based devices, respectively. Best results are obtained for devices with 28% Al that exhibit a broad external quantum efficiency covering the full solar spectrum with a maximum of 80% at 750 nm, an open-circuit voltage of 0.39 V, a short-circuit current density of 17.1 mA/cm2 and a conversion efficiency of 2.12% under air mass 1.5 global (AM1.5G) illumination (1 sun), rendering them promising for novel low-cost III-nitride on Si photovoltaic devices. For Al contents above 28%, the electrical performance of the structures lessens due to the high top-contact resistivityThis research was funded by the national projects from the Ministry of Research and Innovation TEC2017-84378-R and NERA (RTI2018-101037-B-I00); the projects from the Comunidad de Madrid SINFOTON2-CM (P2018/NMT-4326), MADRID-PV2 (P-2018/EMT-4308) and SOLA (CM/JIN/2019-013); the projects from the University of Alcalá ANIS (CCG2018/EXP-042) and PISA (CCG19/IA-005); and by the FEDER program. R. Blasco acknowledges the financial support of his contract associated with the Ramon y Cajal Fellowship RYC-2013-1408

Development of AlInN photoconductors deposited by sputtering

In this work, we have developed photoconductor devices based on Al0.39In0.61N layers grown on sapphire by reac-tive radio-frequency magnetron sputtering. The fabricat-ed devices show a sublinear dependence of the photocur-rent as a function of the incident optical power. The above-the-band-gap responsivity reaches 7 W/A for an ir-radiance of 10 W/m2 (405 nm wavelength). The response decreases smoothly for below-the-bandgap excitation, dropping by more than an order of magnitude at 633 nm. The devices present persistent photoconductivity effects associated to carrier trapping at grain boundaries.Ministerio de Economía y CompetitividadComunidad de MadridUniversidad de Alcal

Two-step method for the deposition of AlN by radio frequency sputtering

This paper presents a detailed study of the influence of deposition conditions on structural and morphological properties of AlN thin films synthesized on c-sapphire substrates by radio frequency (RF) reactive sputtering. After the optimization of deposition parameters such as RF power and substrate temperature, the substrate bias has been identified as a critical variable to improve the structural properties of the AlN layers. The use of negative bias leads to a decrease of the full-width at half-maximum (FWHM) of the rocking curve of the AlN( 0002) x-ray reflection and an increase of the grain size. However, 2θ/ω x-ray scans of layers grown under negative bias reveal lattice disorder at the AlN/sapphire interface, which is attributed to the highly accelerated positive ions (Al+, N+, N2 +) arriving to the substrate at the initial stages of the deposition process. In order to prevent this interface degradation, we propose a twostep deposition methodwhich consists of starting the growth with an unbiased AlN buffer layer, at least 30 nm thick, followed by AlN deposition under negative bias. This procedure results in high-quality AlN layers with FWHM of the rocking curve of the (0002) reflection of 1.63°, grain size of ~40 nm and root-mean-square surface roughness of 0.4 nm

Carrier localization in InN/InGaN multiple-quantum wells with high In-content

We study the carrier localization in InN/In0.9Ga0.1N multiple-quantum-wells (MQWs) and bulk InN by means of temperature-dependent photoluminescence and pump-probe measurements at 1.55 lm. The S-shaped thermal evolution of the emission energy of the InN film is attributed to carrier localization at structural defects with an average localization energy of 12 meV. Carrier localization is enhanced in the MQWs due to well/barrier thickness and ternary alloy composition fluctuations, leading to a localization energy above 35 meV and longer carrier relaxation time. As a result, the luminescence efficiency in the MQWs is improved by a factor of five over bulk InN.European CommissionMinisterio de Ciencia e InnovaciónComunidad de Madri

Carrier localization in InN/InGaN multiple-quantum wells with high In-content

We study the carrier localization in InN/In0.9Ga0.1N multiple-quantum-wells (MQWs) and bulk InN by means of temperature-dependent photoluminescence and pump-probe measurements at 1.55 lm. The S-shaped thermal evolution of the emission energy of the InN film is attributed to carrier localization at structural defects with an average localization energy of 12 meV. Carrier localization is enhanced in the MQWs due to well/barrier thickness and ternary alloy composition fluctuations, leading to a localization energy above 35 meV and longer carrier relaxation time. As a result, the luminescence efficiency in the MQWs is improved by a factor of five over bulk InN.European CommissionMinisterio de Ciencia e InnovaciónComunidad de Madri

High quality Al0.37In0.63N layers grown at low temperature (< 300 degrees 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 degrees 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 degrees 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 degrees C on sapphire and glass substrates is of similar to 2.4 eV while it red shifts to similar to 2.03 eV at 300 degrees 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

Novel InN/InGaN multiple quantum well structures for slow‐light generation at telecommunication wavelengths

The third order susceptibility is responsible for a variety of optical non-linear phenomena -like self focusing, phase conjugation and four-wave mixing- with applications in coherent control of optical communication. InN is particularly attractive due to its near-IR bandgap and predicted high nonlinear effects. Moreover, the synthesis of InN nanostructures makes possible to taylor the absorption edge in the telecomunication spectral range and enhance nonlinear parameters thanks to carrier confinement. In this work, we assess the nonlinear optical behavior of InN/InxGa(1-x)N (0.9 > x > 0.7) multiplequantum-well (MQW) structures grown by plasma-assisted MBE on GaN-on-sapphire templates. Low-temperature (5 K) photoluminescence measurements show near-IR emission whose intensity increases with the In content in the barriers, which is explained in terms of the existence of piezoelectric fields in the structures. The nonlinear optical absorption coefficient, α2, were measured at 1.55 μm using the Z-scan method. We observe a strong dependence of the nonlinear absorption coefficient on the In content in the barriers. Saturable absorption is observed for the sample with x = 0.9, with α2 ̃ -9x103 cm/GW. For this sample, an optically controlled reduction of the speed of light by a factor S ∼ 80 is obtained at 1.55 μm. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA

High-sensitive SPR sensing with Indium Nitride as a dielectric overlay of optical fibers

In this work, an Indium Nitride (InN) dielectric overlay has been used to develop a surface plasmon resonance optical fiber sensor. Although InN is a very promising material in electronics industry, this is the first time that this kind of material is used for optical sensing. The obtained results show an improvement of the reliability and long term stability with respect to previous devices made with the same technology. More remarkably, the sensitivity increases up to 11,800 nm/RIU in the range of outer refractive indices between 1.415 and 1.429, the highest sensitivity achieved with this kind of devices. Therefore, a novel application of the InN to optical fiber sensors is demonstrated. The use of this material would be of great interest to produce new SPR-based devices for chemical and biological sensing

Non-linear absorption of InN/InGaN multiple-quantum-well structures at optical telecommunication wavelengths

We report on the nonlinear optical absorption of InN/ InxGa1−xN x=0.8, 0.9 multiple-quantum-well structures characterized at 1.55 m by the Z-scan method in order to obtain the effective nonlinear absorption coefficient 2 of the samples at high repetition rate. Saturable absorption is observed for the sample with x=0.9, with an effective 2 −9 103 cm/GW for the studied optical regime. For lower In content in the barrier, reverse saturable absorption is observed, which is attributed to two-photon absorption.Ministerio de Ciencia e InnovaciónComunidad de Madri