Phase change materials (PCM) have gained a considerable interest in the photonics community as active materials in reconfigurable devices. Their significant change of optical properties upon the amorphous to crystalline reversible phase transition enables a large and dynamical tuning of devices’ response. Among the various PCM, Ge2Sb2Te5 (GST) is the most widely used thanks to its fast phase change as well as the large modulation of its refractive index (Δn > 1). Although this PCM has been mainly exploited for simple binary on-off functions, it presents an additional degree of freedom: the multi-level partial change of state. Indeed, we show in this paper multi-level continuously tunable reflectivity allowed by the electrically-controlled partial crystallization of GST. This is achieved via the Joule effect, by injecting short voltage pulses (few tens of μs) through platinum microheaters underneath GST patches. This electrically-induced phase transition is the most promising strategy for PCM integration in industrial foundries and shows promises for individual pixel addressing in multi-level applications such as neuromorphic computing or grayscale displays.
Recently, fluorescent point defects in silicon have been explored as promising candidates for single photon sources, which may pave the way towards the integration of quantum photonic devices with existing silicon-based electronic platforms. However, the current processes for creating such defects are complex, and commonly require one or two implantation steps. In this work, we have demonstrated implantation-free methods for obtaining G and W-centers in commercial silicon-on-insulator substrates using femtosecond laser annealing. We also demonstrate an enhancement of the color centers’ optical properties by coupling them with photonic structures. For example, we have shown an improvement in emission directivity for G centers by embedding them into silicon Mie resonators fabricated by dewetting, achieving an extraction efficiency exceeding 60% with standard numerical apertures. We will also address the control of emission polarization by embedding color centers in photonic crystals.
Phase change materials (PCMs) are currently revolutionizing nanophotonics by providing ways to tune and reconfigure optical functionalities without any moving parts. Building on this phenomenon, the last decade has witnessed many exciting reports of novel devices exploiting PCMs such as for example beam-steering, tunable light emission, reflection and absorption, programmable metasurfaces and reconfigurable neural networks. A large majority of the first studies were using standard PCMs such as GeSbTe as simple binary on-off switches, in which the ON state is the amorphous phase and the OFF state the fully crystalline phase. However, PCMs present another degree of freedom for tunability: the possibility to encode multilevel non-volatile states via partial crystallization. Furthermore, recently a new class of low-loss PCMs emerged (e.g. Sb2S3 and Sb2Se3), with negligible optical absorption in the near-infrared.
In this paper, we will present recent results on methods to program PCMs into various multilevel states of crystallization. We will then present nanophotonic devices leveraging this multilevel programming and conclude on the perspectives for this technology.
We report on the synthesis of 2D GaN materials by the so-called liquid metal chemistry and tuning of their composition between oxide and nitride materials. This technique promises easier integration of 2D materials onto photonic devices compared to traditional “top-down” and “bottom-up” methods. Our fabrication method is carried out via a two-step liquid metal-based printing method followed by a microwave plasma-enhanced nitridation reaction. The synthesis of GaN relies on plasma-treated liquid metal-derived two-dimensional (2D) sheets that were squeeze-transferred onto desired substrates. We characterized the composition and optical properties of the resulting nm-thick GaN films using AFM, XPS, and ellipsometry measurements. Finally, the optical indices measured by ellipsometry are compared with theoretical results obtained by density functional theory (DFT). Our results represent a first step toward integrating 2D materials and semiconductors into electronics and optical devices.
We present a study on erbium (Er)-doped silicon (Si)-rich silicon oxide thin films grown by the magnetron cosputtering of three confocal cathodes according to the deposition temperature and the annealing treatment. It is shown that, through a careful tuning of both deposition and annealing temperatures, it is possible to engineer the fraction of agglomerated Si that may play the role of sensitizer toward Er ions. To investigate the different emitting centers present within the films according to the fraction of agglomerated Si, a cathodoluminescence experiment was made. We observe in all samples contributions from point-defect centers due to some oxygen vacancies and generally known as silicon-oxygen deficient centers (SiODC), at around 450-500 nm. The behavior of such contributions suggests the possible occurrence of an energy transfer from the SiODCs toward Er3+ ions. Photoluminescence experiments were carried out to characterize the energy transfer from Si nanoclusters toward Er3+ ions with a nonresonant wavelength (476 nm) that is unable to excite SiODCs and then exclude any role of these centers in the energy transfer process for the PL experiments. Accordingly, it is shown that structural differences have some effects on the optical properties that lead to better performance for high-temperature deposited material. This aspect is illustrated by the Er-PL efficiency that is found higher for 500°C-deposited, when compared to that for RT-deposited sample. Finally, it is shown that the Er-PL efficiency is gradually increasing as a function of the fraction of agglomerated silicon.
We present a study on erbium-doped silicon rich silicon oxide (SRSO:Er) thin films grown by the magnetron cosputtering
of a three confocal cathodes according to the deposition temperature and the annealing treatment. It is shown
that several parameters such as the stoichiometry SiOx, the Erbium content and the fraction of agglomerated Silicon are
strongly influenced by the deposition temperature. Especially, an increase of the fraction of agglomerated-Si concomitant
to a reduction of the erbium content is observed when the deposition temperature is raised. These structural differences
have some repercussions on the optical properties that lead to better performances for high-temperature deposited
material. It is illustrated by the Er-PL efficiency that is higher for 500°C-deposited than for RT-deposited sample at all
annealing temperatures. Finally an investigation of the different emitting centres within the films is performed with a
cathodoluminescence technique to highlight the emission of optically-active defect centers in the matrix. It is shown that
some oxygen vacancies, namely Silicon-Oxygen Deficient Centers, have a strong contribution around 450-500 nm and
are suspected to contribute to the energy transfer towards Er3+ ions.
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