In-rich InGaN/GaN nanowires (NWs) are key optoelectronic materials, which can close the green gap of the light emitting diodes and can be used in efficient high-bandgap solar cells for integration in tandem devices. Realization of these devices requires as a first step the optimization of the NW structure and their electrical parameters. Electron Beam Induced Current (EBIC) microscopy is well suited to probe nanoscale devices with a high resolution and to extract the material parameters.
Here, we analyze the electrical properties of axial GaN and InGaN/GaN n-p and p-n junction NWs using EBIC microscopy. III-N NWs were grown on Si(111) substrates by molecular beam epitaxy using Mg as a p-dopant and Si as an n-dopant. The growth conditions were adjusted to optimize the doping order with an abrupt axial junction without a parasitic radial overgrowth. From the EBIC analysis of the GaN p-n junctions, the doping level and the minorities carrier diffusion lengths were extracted. Next, a p-GaN/i-InGaN/n-GaN junction containing an In-rich InGaN segment [1] was grown yielding a flat and strong EBIC signal in the InGaN NW portion. NW arrays were then contacted and their behavior under visible light was analyzed.
[1] Morassi et al., Cryst. Growth Des., 2545, 18 2018
“Photonics Multiannual Strategic Roadmap 2014-2020” mentions flexible electronics, light sources, displays, sensors and solar cells as key emerging technologies with a high expected growth of the market share. Technologies based on organic semiconductors still suffer from a short lifetime and low efficacy as compared to their inorganic counterparts. To make a flexible device from inorganic semiconductors one should shrink the size of the active elements and to integrate them on mechanically-flexible substrates. This can be achieved using control-by-design nanowires.
In this work, we address the growth of nitride nanowires on novel substrates and the fabrication and characterization of flexible devices based on nitride nanowires. First, we will discuss the epitaxy of GaN nanowires on graphene-on-SiO2 substrates. We show that without any catalyst or intermediate layer, the nanowires grow on graphene with an excellent selectivity compared to the uncovered SiO2 surface. Taking advantage of this selectivity, we demonstrate that organized arrays of nanowires can be synthesized by structuring the graphene layer. Next, we will discuss the approach for nanowire lift-off, transfer into polymer-embedded membranes and flexible contacting. The realization and characterization of flexible light sources, photodetectors and piezogenerators will be presented.
Microphotoluminescence experiment has been performed on InAsP/InP epitaxial quantum dots,
emitting in the telecommunication wavelength range. The exciton emission from a single quantum
dot has been detected via the excitation power dependence of the microphotoluminescence spectra.
Two photon entanglement schemes are proposed in order to produce entangled photons out of the
excitonic and bexcitonic transitions in such dot. Both schemes require the implementation of Purcell
effect, in order to collect efficiently the emitted photons and to restore entanglement.
Single photon sources are of extreme interest for future quantum communications networks. Several realizations of such sources where proposed but none of them corresponds to the needs of a quantum network, in terms of emission wavelength, repetition rate or quantum state purity. Using self organized InAs/InP quantum dots, it is
possible to tune the emission wavelength up to 1.55 μm. Lifetime measurements confirm the high optical quality of these dots opening the possibility to engineer sources operate above 77K. With this material combination it is also possible to localized the growth of a single quantum dot, that can be to deterministically coupled to a
photonic crystal cavity.
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