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The family of van der Waals (vdW) materials is large and diverse with applications ranging from electronics and optoelectronics to catalysis and chemical storage. However, despite intensive research, there remains significant knowledge-gaps pertaining to their properties and interactions. One such gap is the interaction between these materials and hydrogen, a potentially vital future energy vector and ubiquitous processing gas in the semiconductor industry. This work reports on the interaction of hydrogen with the vdW semiconductor SnS2, where molecular hydrogen (H2) and H-ions induce a controlled chemical conversion into semiconducting-SnS or to ?-Sn. This hydrogen-driven reaction is facilitated by the different oxidation states of Sn and is successfully applied to form SnS2/SnS heterostructures with uniform layers, atomically flat interfaces and well-aligned crystallographic axes. This approach is scalable and offers a route for engineering materials at the nanoscale for semiconductor technologies based on the earth-abundant elements Sn and S, a promising result for a wide range of potential applications.

In dilute nitride InyGa1-yAs1-xNx alloys, a spatially controlled tuning of the energy gap can be realized by combining the introduction of N atoms-inducing a significant reduction of this parameter-with that of hydrogen atoms, which neutralize the effect of N. In these alloys, hydrogen forms N-H complexes in both Ga-rich and In-rich N environments. Here, photoluminescence measurements and thermal annealing treatments show that, surprisingly, N neutralization by H is significantly inhibited when the number of In-N bonds increases. Density functional theory calculations account for this result and reveal an original, physical phenomenon: only in the In-rich N environment, the InyGa1-yAs host matrix exerts a selective action on the N-H complexes by hindering the formation of the complexes more effective in the N passivation. This thoroughly overturns the usual perspective of defect-engineering by proposing a novel paradigm where a major role pertains to the defect-surrounding matrix.

Owing to their ability to generate non-classical light states, quantum dots (QDs) are very promising candidates for the large-scale implementation of quantum information technologies. However, the high photon collection efficiency demanded by these technologies may be impossible to reach for “standalone” semiconductor QDs, embedded in a high-refractive index medium. In this work a novel laser writing technique is presented, enabling the direct fabrication of a QD self-aligned—with a precision of ±30 nm—to a dielectric microsphere. The presence of the microsphere leads to an enhancement of the QD luminescence collection by a factor 7.3 ± 0.7 when an objective with 0.7 numerical aperture is employed. This technique exploits the possibility of breaking the N−H bonds in GaAs (Formula presented.) Nx:H by a laser light, obtaining a lower-bandgap material, GaAs (Formula presented.) Nx. The microsphere, deposited on top of a GaAs (Formula presented.) Nx:H/GaAs quantum well, is used to generate a photonic nanojet, which removes hydrogen exactly below the microsphere, creating a GaAs (Formula presented.) Nx QD at a predefined distance from the sample surface. Second-order autocorrelation measurements confirm the ability of the QDs obtained with this technique to emit singlephotons.

International audience; BULLKID is an R&D project on a cryogenic particle detector to search for rare low-energy processes such as low-mass dark matter and neutrino coherent scattering off nuclei. The detector unit we are designing consists in an array of ~ 100 silicon absorbers sensed by phonon-mediated, microwave-multiplexed kinetic inductance detectors, with energy threshold below 100 eV and total target mass around 30 g. The single detector unit will be engineered to ensure a straightforward scalability to a future kg-scale experiment.

OLIMPO is a balloon-borne experiment aiming at spectroscopic measurements of the Sunyaev-Zel’dovich effect in clusters of galaxies. The instrument operates from the stratosphere, so that it can cover a wide frequency range (from ∼ 130 to ∼ 520 GHz in 4 bands), including frequencies which are not observable with ground-based instruments. OLIMPO is composed of a 2.6-m aperture telescope, a differential Fourier transform spectrometer and four arrays of lumped element kinetic inductance detectors operating at the temperature of 0.3 K. The payload was launched from the Longyearbyen airport (Svalbard Islands) on July 14th, 2018, and operated for 5 days, at an altitude of 38 km around the North Pole. We report the in-flight performance of the first lumped element kinetic inductance detector arrays ever flown onboard a stratospheric balloon.

International audience; The CALDER project aims to realize cryogenic light detectors for the next generation of experiments searching for rare events. More in detail, the main application of these devices will be the background suppression in future cryogenic calorimetric experiments searching for neutrinoless double beta decay ($0\nu $DBD). This is the case of CUPID, a next-generation $0\nu $DBD observatory, able to take advantage from particle identification to dramatically reduce the background events. In this contribution, we show the status of the CALDER project. The light sensors developed in this R&D are based on kinetic inductance detector operated in the phonon-mediated approach. Their energy resolution (20 eV), time response ($\upmu $s) and multiplexing capability make them very promising for the future CUPID experiment.

Over the last few years, kinetic inductance detectors (KIDs) became the object of increasing interest as photon and phonon detectors. From this perspective, the pulse response of such detectors deserves an in-depth study. In most applications, the sensitivity of the KID is ultimately limited by the white noise from the cryogenic amplifier, which is reduced by increasing the power supplied to the device. On the other hand, a high readout power leads to a nonlinear response of the microresonator, originating from the dependence on the current acquired by the kinetic inductance. This paper describes a model for the response to optical pulses of a KID driven to the nonlinear regime, taking into account not only the electrical effects but also the thermal ones induced by power absorption. The model has been validated on data collected using an aluminium resonator developed within the CALDER project (http://www.roma1.infn.it/exp/calder/).

Kinetic Inductance Detectors (KIDs) are superconductive low$-$temperature detectors useful for astrophysics and particle physics. We have developed arrays of lumped elements KIDs (LEKIDs) sensitive to microwave photons, optimized for the four horn-coupled focal planes of the OLIMPO balloon-borne telescope, working in the spectral bands centered at 150 GHz, 250 GHz, 350 GHz, and 460 GHz. This is aimed at measuring the spectrum of the Sunyaev-Zel'dovich effect for a number of galaxy clusters, and will validate LEKIDs technology in a space-like environment. Our detectors are optimized for an intermediate background level, due to the presence of residual atmosphere and room--temperature optical system and they operate at a temperature of 0.3 K. The LEKID planar superconducting circuits are designed to resonate between 100 and 600 MHz, and to match the impedance of the feeding waveguides; the measured quality factors of the resonators are in the $10^{4}-10^{5}$ range, and they have been tuned to obtain the needed dynamic range. The readout electronics is composed of a $cold$ $part$, which includes a low noise amplifier, a dc$-$block, coaxial cables, and power attenuators; and a $room-temperature$ $part$, FPGA$-$based, including up and down-conversion microwave components (IQ modulator, IQ demodulator, amplifiers, bias tees, attenuators). In this contribution, we describe the optimization, fabrication, characterization and validation of the OLIMPO detector system., Proceedings of WOLTE13, September 10-13, 2018 Sorrento, Italy

Kinetic Inductance Detectors made of High-TC superconductor YBCO are designed and fabricated, in view as possible application as high sensitivity, low cost and high-manageability terahertz camera for imaging.

The inherent ability of plasmonic bowtie nanoapertures (NAs) to localize the electromagnetic field at a subwavelength scale was exploited to engineer the H removal process in dilute nitrides at the nanometer level. Dilute nitride semiconductor alloys (e.g. GaAsN with a small percentage of nitrogen) are characterized by peculiar optoelectronic properties and, most importantly, by an even more peculiar response to hydrogen incorporation. In this class of materials, it is indeed possible to tune post-growth the alloy bandgap energy by a controlled incorporation of hydrogen atoms. The formation of N-H complexes neutralizes all the effects N has on the host matrix, among which is the strong narrowing of bandgap energy. In the present work, bowtie NAs resonant to the N-H complex dissociation energy were numerically modeled by finite element method simulations, realized by a lithographic approach, and characterized by scanning probe microscopy and resonant scattering spectroscopies. The conditions to get the maximum field enhancement at a specific position below the metal/semiconductor interface, namely at the dilute nitride quantum well position, were identified, demonstrating the ability to achieve a plasmon-assisted spatially selective hydrogen removal in a GaAsN/GaAs quantum well sample. Hydrogen removal through bowtie NAs turns out to be way more efficient (approximately two orders of magnitude) than through the plain surface, thus indicating that bandgap engineering through plasmonic nanostructures can be optimized for future efficient realization of site-controlled single-photon emitters and for their deterministic integration in plasmonic devices.

Circularly dichroic metasurfaces are highly sought for a plethora of applications; while many alternative options are present in the literature, it is hard to select an approach that combines high circular dichroism (CD) with stable performances and easy reproducibility. In this work, we have designed and experimentally investigated a planar plasmonic metamaterial based on a comma-shaped geometry, which features such characteristics. We have focused the complexity of realization in the design process, which combines intrinsic chirality and high field localization, while fabrication was executed by using a standard single-step lift-off procedure. We have produced two classes of samples, closely related in shape but differing slightly in designing method and results, both reaching high levels of CD. Experiments on the first reveal the sensibility of the metasurface to geometrical variations due to fabrication non-idealities, as often happens in metamaterials based on surface plasmons and resonances; on the other hand, with the second, we demonstrate that it is possible to guarantee stable peak values on specific wavelength ranges, even when dealing with relevant fabrication tolerances. Moreover, numerical analyses suggest the possibility to reach values converging toward unity. The ease of implementation by using standard fabrication procedures and the robustness of the performance even with fabrication imprecisions make our proposed metamaterial eligible for adoption for further research in high-precision spectroscopy and implementation at industrial scale. (C) 2019 Optical Society of America

The GaAs-like longitudinal-optical (LO) phonon frequency in hydrogenated GaAsN (x = 0.01) layers - with different H doses and similar low-energy irradiation conditions - was investigated by micro-Raman measurements in different scattering geometries and compared with those of epitaxial GaAs and as-grown GaAsN reference samples. A relaxation of the GaAs selection rules was observed, to be explained mainly on the basis of the biaxial strain affecting the layers. The evolution of the LO phonon frequency with increasing hydrogen dose was found to heavily depend on light polarization, thus suggesting that a linear relation between strain and the frequency of the GaAs-like LO phonon mode should be applied with some caution. Moreover, photoreflectance measurements in fully passivated samples of identical N concentration show that the blueshift of the GaAs-like LO frequency, characteristic of the hydrogenated structures, is dose-dependent and strictly related to the strain induced by the specific type of the dominant N-H complexes. A comparison of photoreflectance results with the finite element method calculations confirms that this dependence on the H dose is due to the gradual replacement of the N-2H complexes responsible for the electronic passivation of N with N-3H complexes, which are well known to induce an additional and sizeable lattice expansion.

International audience; We report on the performance of lumped-elements Kinetic Inductance Detector (KID) arrays for mm and sub-mm wavelengths, operated at 0.3 K during the stratospheric flight of the OLIMPO payload, at an altitude of 37.8 km. We find that the detectors can be tuned in-flight, and their performance is robust against radiative background changes due to varying telescope elevation. We also find that the noise equivalent power of the detectors in flight is smaller by a factor of ~ 2, 8, 3.5, 4.5 at 150, 250, 350 and 460 GHz relative to the one measured in the laboratory, and is close to our calculated photon-noise-limited performance. The effect of primary cosmic rays crossing the detector is found to be consistent with the expected ionization energy loss with phonon-mediated energy transfer from the ionization sites to the resonators. In the OLIMPO detector arrays, at float, cosmic ray events affect less than 4% of the detector samplings for all the pixels of all the arrays, and less than 1% of the samplings for most of the pixels. These results are also representative of what one can expect from primary cosmic rays in a satellite mission with similar KIDs and instrument environment.

In this review, we report on the design, fabrication, and characterization of photonic crystal arrays, made of two and three coupled nanocavities. The properties of the cavity modes depend directly on the shape of the nanocavities and on their geometrical arrangement. A non-negligible role is also played by the possible disorder because of the fabrication processes. The experimental results on the spatial distribution of the cavity modes and their physical characteristics, like polarization and parity, are described and compared with the numerical simulations. Moreover, an innovative approach to deterministically couple the single emitters to the cavity modes is described. The possibility to image the mode spatial distribution, in single and coupled nanocavities, combined with the control of the emitter spatial position allows for a deterministic approach for the study of cavity quantum electrodynamics phenomena and for the development of new photonic-based applications., M.F. and A.P. acknowledge support by Sapienza Università di Roma under the “Ricerche Ateneo” Grants 2016 and 2017. F.B., M.F. and G.P. also acknowledge support and funding from the Italian Ministry for Education, University and Research within the Futuro in Ricerca (FIRB) program (project DeLIGHTeD, Prot. RBFR12RS1W). The work of F.B. was partially supported by Fondazione Ente Cassa di Risparmio di Firenze within the project PERBACCO (no. 2016.1084). A.P and M.F. have also received funding from the LazioInnova project “SINFONIA”, (Prot. n. 85-2017-15200)., We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI)

We addressed the issue of atomic ordering in a series of In-rich In xGa 1 − xN epilayers grown on a GaN/AlN/sapphire(0001) epitaxial template by quantitatively measuring the Ga-cation coordination in the second atomic shell of Ga. We used Diffraction Anomalous Fine Structure Spectroscopy (DAFS) at the Ga K-edge to select the signal coming from the Ga atoms in the epilayer and eliminate any contribution from the buffer layer. DAFS measurements were also performed on hydrogenated epilayers in order to investigate the possible formation of Ga-H complexes. We find that deviation from cation random distribution in the form of Ga clustering is present in both untreated and hydrogenated samples and that in the latter ones the second atomic shell around Ga is modified, suggesting an additional perturbation of the cation sublattice related to hydrogen. However, comparing the present results with In K-edge x-ray absorption spectra previously reported, we conclude that the formation of Ga-H complexes vs. In-H ones is unlikely. Cation clustering has to be anyway taken into account as a possible channel playing in the determination of the optical bandgap of these technology-oriented semiconductors.We addressed the issue of atomic ordering in a series of In-rich In xGa 1 − xN epilayers grown on a GaN/AlN/sapphire(0001) epitaxial template by quantitatively measuring the Ga-cation coordination in the second atomic shell of Ga. We used Diffraction Anomalous Fine Structure Spectroscopy (DAFS) at the Ga K-edge to select the signal coming from the Ga atoms in the epilayer and eliminate any contribution from the buffer layer. DAFS measurements were also performed on hydrogenated epilayers in order to investigate the possible formation of Ga-H complexes. We find that deviation from cation random distribution in the form of Ga clustering is present in both untreated and hydrogenated samples and that in the latter ones the second atomic shell around Ga is modified, suggesting an additional perturbation of the cation sublattice related to hydrogen. However, comparing the present results with In K-edge x-ray absorption spectra previously reported, we conclude that the formation of Ga-H complexes vs. In-H...

We provide a brief survey of the most recent results obtained by performing spatially selective hydrogen irradiation of dilute nitride semiconductors. The striking effects of the formation of stable N-H complexes in these compounds - coupled to the ultrasharp diffusion profile of H therein - can be exploited to tailor the structural (lattice constant) and optoelectronic (energy gap, refractive index, electron effective mass) properties of the material in the growth plane, with a spatial resolution of a few nm. This can be applied to the fabrication of site-controlled quantum dots (QDs) and wires, but also to the realization of the optical elements required for the on-chip manipulation and routing of qubits in fully integrated photonic circuits. The fabricated QDs - which have shown the ability to emit single photons - can also be deterministically coupled with photonic crystal microcavities, proving their inherent suitability to act as integrated light sources in complex nanophotonic devices.

Substitution of constituent atoms and/or changes of crystal structure are routinely used to tailor the fundamental properties of a semiconductor. Here, it is shown that such a tailoring can also be realized thanks to a novel hydrogen effect. Four hydrogen atoms can screen the effect the crystal potential has on a constituent cation, thus generating a solitary cation: an effectively isolated impurity, so chemically different from the unscreened constituent cations that it strongly perturbs the electronic properties of the material by increasing its fundamental band-gap energy. Such a hydrogen-induced screening effect is removed by thermal treatments, thus permitting reversible modifications of both the "crystal chemistry" and material's properties. This phenomenon, observed in InN and other topical nitrides, should permit the development of a new class of materials as well as the fabrication of photonic devices and optical integrated circuits with distinct, tailor-made r egions emitting or absorbing light, all integrated onto a monolithic semiconductor structure. Fundamental properties of nitrides are changed through deep modifications of the chemistry of their constituent atoms induced by atomic hydrogen. In InN, for example, an In cation is isolated from its crystalline environment by the cooperative action of four hydrogen atoms that locally screen the crystal potential, thus generating a "solitary cation" (In) that remarkably increases the InN fundamental band-gap energy.

The electronic properties of In(AsN) before and after post-growth sample irradiation with increasing doses of atomic hydrogen have been investigated by photoluminescence. The electron density increases in In(AsN) but not in N-free InAs, until a Fermi stabilization energy is established. A hydrogen epsilon+/− transition level just below the conduction band minimum accounts for the dependence of donor formation on N, in agreement with a recent theoretical report highlighting the peculiarity of InAs among III–V compounds. Raman scattering measurements indicate the formation of N–H complexes that are stable under thermal annealing up to ~500 K. Finally, hydrogen does not passivate the electronic activity of N, thus leaving the band gap energy of In(AsN) unchanged, once more in stark contrast to what has been reported in other dilute nitride alloys.

In dilute nitrides [e.g., Ga(AsN), (InGa)(AsN)] the formation of stable N-2H-H complexes following H irradiation removes the effects nitrogen has on the optical (i.e., refractive index [1]), structural [2], and electronic [3] properties of the material. In particular, H binding to N atoms in GaAs1-xNx leads to an increase in the band gap energy of the N-containing material (~1.33 eV for x = 1% at T = 5 K) up to the value it has in GaAs (1.52 eV at 5 K). Therefore, by allowing H incorporation only in selected regions of the sample - e.g., by deposition of H-opaque masks prior to the hydrogenation - it is possible to attain a spatially controlled modulation of the band gap energy in the growth plane. This technique, referred to as in-plane Band Gap Engineering, can be employed to tailor the carrier-confining potential down to a nm scale, resulting in the fabrication of site-controlled, dilute nitride-based quantum dots (QDs). We demonstrate here that such QDs emit single photons on demand, as revealed by measuring the second-order correlation function of the single-exciton emission [4].Coupled to the possibility of erasing/rewriting the fabricated patterns through multiple annealing/hydrogenation procedures, the inherently precise control over the position of the nanostructures fabricated with this method renders them naturally suited for the integration with photonic crystal nanocavities.

The effects of external perturbations-such as temperature, photo-excited carrier density, and magnetic field-on the electronic properties of Ga(AsBi) alloys are investigated in a large range of Bi-concentration (x up to similar to 11%). These studies allow us to disclose the existence of Bi-induced localized states that largely contribute to the recombination spectra up to relatively-high temperature (T similar to 150 K). The sensitivity of the band-gap energy to temperature variation is found to diminish strongly with Bi-concentration and to result in a reduction of about a factor of two at the highest concentrations. Magneto-photoluminescence studies have also revealed the role exerted by the Bi-induced levels on the host band states and have disclosed an unexpectedly strong carrier-carrier scattering, which hampers the observation of Landau-level quantization at low magnetic fields. An unusual compositional dependence of the exciton reduced mass, as well as an unexpected increase of the electron effective mass at relatively-low Bi-concentration (x < 6%), are reported and related to the presence of Bi-induced states.

We report on the tuning of the spectral response of superlattice (SL) diodes based on dilute nitride Ga(AsN) alloys by post-growth hydrogenation. Hydrogen is incorporated into the superlattice where it neutralizes the electronic activity of nitrogen by forming N-H complexes. We exploit the controlled thermal dissociation of the complexes to tune the energy of the SL photocurrent absorption and electroluminescence emission; also, by annealing a submicron spot with a focused laser beam we create a preferential path for the injection of carriers, thus activating a nanoscale light emitting region. This method can be used for fabricating planar diode arrays with distinct optical active regions, all integrated onto a single substrate.\ud \ud This work was supported by the University of Nottingham, the EU (under Grant Agreement No. PIEF-GA-2010-272612), the Italian MIUR (under FIRB 2012 project DeLIGHTeD, prot. RBFR12RS1W), and the EPSRC. We acknowledge useful discussions with Professor Mario Capizzi and Professor Antonio Polimeni (Sapienza Università di Roma).

We investigated atomic ordering in In-rich In x Ga1−x N epilayers in order to obtain an understanding of whether a deviation from a random distribution of In atoms in the group-III sublattice could be the origin of the strong carrier localization and defect-insensitive emission of these semiconductor alloys. This phenomenon can be exploited for application in optoelectronics. By coupling In K-edge x-ray absorption spectroscopy and high resolution x-ray diffraction, we were able to discard the hypothesis of significant phase separation into InN + GaN, in agreement with previous N K-edge absorption spectroscopy. However, we found an enrichment of In neighbours in the second atomic shell of In as compared to random statistics (clustering) for x = 0.82, while this is not the case for x = 0.46. This result, which is also supported by optical spectroscopy, is likely to stimulate new theoretical studies on In x Ga1−x N alloys with a very high In concentration.

We report on the fabrication of a micrometer-size movable light emitting area in a GaAs/AlAs quantum well resonant tunneling p-i-n diode. The spatial position of the micrometer-size light emitting area shifts linearly with increasing applied bias, up to 30 μm for a bias increment of 0.2 V. Also, the simultaneous resonant tunneling injection of both electrons and holes into the quantum well states is achieved at specific positions of the diode, thus resulting in a tenfold increase of the electroluminescence intensity.\ud \ud This work was supported by the EU (under Grant Agreement No. PIEF-GA-2010-272612), The Royal Society (RG110416), The University of Nottingham, and the Italian MIUR (under the FIRB project DeLIGHTeD, Prot. RBFR12RS1W). We thank the EPSRC National Center for III–V Technologies (K. Kennedy and R. Airey) for device processing and A. Nasir (The University of Nottingham) for assistance during sample preparation.

The properties of InGaAsN V-groove QWRs are assessed here by polarization-dependent photoluminescence (PL) and micro-magneto-PL. Both the polarization anisotropy of the QWR emission and the strong dependence of the diamagnetic shift on the orientation of the applied magnetic field confirm the 1D nature of the QWR excitons. Further, the possibility of passivating N impurities by H irradiation is used to estimate the N content (x) in the QWRs by turning off the effects of N incorporation. Both the H-induced blueshift of the QWR emission (70 meV) and the measured value of the electron effective mass are consistent with x similar to 1%. Nitrogen is also found to enhance the In intake in the QWR, likely due to the strain reduction resulting from the smaller lattice parameter of the InGaAsN alloy. Such strain reduction is also responsible for the quick decay of the degree of linear polarization (rho) of the QWR emission with increasing temperature, indicating a small splitting between the QWR valence-band levels. In fully hydrogenated samples, conversely, rho remains roughly constant up to similar to 240 K, suggesting the recovery of a larger energy separation between the QWR hole states upon N passivation. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

We report p-type conductivity in nominally undoped GaAs1–xBix epilayers for a wide range of Bi-concentrations (0.6% ≤ x ≤ 10.6%). The counterintuitive increase of the conductivity with increasing x is paralleled by an increase in the density of free holes by more than three orders of magnitude in the investigated Bi-concentration range. The p-type conductivity results from holes thermally excited from Bi-induced acceptor levels lying at 26.8 meV above the valence band edge of GaAs1−xBix with concentration up to 2.4 × 1017 cm−3 at x = 10.6%.

The effects of hydrogen incorporation on the electronic properties of Ga(AsBi) alloys are investigated in a wide range of Bi-concentration (0.6% ≤ x ≤ 10.6%) by Hall effect measurements in magnetic fields up to 14 T and by photoluminescence spectroscopy. For all the investigated Bi-concentrations, we report the passivation of Bi-induced shallow acceptor levels—responsible for the native p-type conductivity in Ga(AsBi)—and a tenfold increase of the hole mobility upon hydrogen incorporation in the host lattice. The emission energy is, instead, negligibly affected by hydrogenation, indicating that the narrowing of the band-gap energy with Bi and the native p-type conductivity are two uncorrelated effects arising from different Bi-induced electronic levels. Passivation by hydrogen of the shallow Bi-acceptor levels makes also possible to identify deep Bi-acceptor states.

Theoretical basis and typical experimental setups of photoluminescence, PL, are briefly described. The investigation by PL of some of the fundamental properties of compound semiconductors and alloys—e.g., optical gap, type and density of shallow impurities, effects of structural disorder in alloys and at heterostructure interfaces, and carrier effective masses—is illustrated. The effects on PL spectra of magnetic fields are discussed, together with the validity limits of perturbation and numerical models for different ratios of magnetic and excitonic energies.

We show that the dissociation of the N-H complex in hydrogenated III-N-Vs can be laser activated at temperatures that are significantly smaller than those (>200°C) required for thermal dissociation due to a resonant photon absorption by the N-H complex. This phenomenon provides a mechanism for profiling the band-gap energy in the growth plane of the III-N-Vs with submicron spatial resolution and high energy accuracy; the profiles are erasable and the alloys can be rehydrogenated making any nanoscale in-plane band-gap profile rewritable. © 2012 American Physical Society.

The multiform donor nature of hydrogen in n- type indium nitride is experimentally observed in samples exposed to atomic hydrogen. Photoluminescence measurements reveal a tenfold increase in the electron concentration and the formation of a shallow donor band upon hydrogen incorporation. Annealing studies show that hydrogen occupies at least two equilibrium sites having almost equivalent thermal stability.

The dependence of the electron mass on hydrostatic pressure $P$ in N-diluted ${\mathrm{GaAs}}_{1\ensuremath{-}x}{\mathrm{N}}_{x}$ ($x=0.10%$ and 0.21%) is investigated by magnetophotoluminescence. Exceedingly large fluctuations (up to $60%/\mathrm{kbar}$) in the electron mass with increasing $P$ are found. These originate from a pressure-driven tuning of the hybridization degree between the conduction band minimum and specific nitrogen-related states. Present results suggest a hierarchy between different nitrogen complexes as regards the extent of the perturbation these complexes exert on the electronic properties of the GaAs host.

The possibility of almost linear tuning of the band gap and of the electrical and optical properties in monolayers (MLs) of semiconducting transition metal dichalcogenide (S-TMD) alloys opens up the way to fabricate materials with on-demand characteristics. By making use of photoluminescence spectroscopy, we investigate optical properties of WSSe MLs with a S/Se ratio of 57/43 deposited on SiO$_2$/Si substrate and encapsulated in hexagonal BN flakes. Similarly to the $"parent"$ WS$_2$ and WSe$_2$ MLs, we assign the WSSe MLs to the ML family with the dark ground exciton state. We find that, in addition to the neutral bright A exciton line, three observed emission lines are associated with negatively charged excitons. The application of in-plane and out-of-plane magnetic fields allows us to assign undeniably the bright and dark (spin- and momentum-forbidden) negative trions as well as the phonon replica of the dark spin-forbidden complex. Furthermore, the existence of the single photon emitters in the WSSe ML is also demonstrated, thus prompting the opportunity to enlarge the wavelength range for potential future quantum applications of S-TMDs., Comment: 6 pages, 5 figures, +ESI