Nano-Structured and flexible LED

Involved people

Permanent staff: Maria Tchernycheva, François Julien, Sophie Bouchoule ,

Postdocs: Junkang Wang  PhDs: Nan Guan, Nuno Amador

Mechanically flexible optoelectronic devices 

The existing limitations of thin film light emitting diode (LED) performance have motivated a strong research effort on nanostructured LEDs as a way to improve the efficiency and to reduce the cost. In particular, nitride nanowires present a large number of advantages for three-dimensional LEDs, namely an improvement of the material quality with respect to thin films, a better handling of the strain induced by thermal expansion mismatch and an improved extraction efficiency. Nanowires can also bring new functionalities, such as the mechanical flexibility.
Flexible electronics, light sources, displays, sensors and solar cells as key emerging technologies with a high expected growth in the coming years. 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

 

  • Flexible Light Emitting Diodes Based on Vertical Nitride Nanowires

We demonstrated fully flexible blue and green LEDs based on core/shell InGaN/GaN nanowires grown by MOCVD. Fully transparent flexible LEDs with a high optical transmittance (60% at λ=530 nm) were also realized. In addition, we demonstrated the integration of green and blue LED membranes into a two-layer bi-color nanowire-based flexible LED. The two layers containing InGaN/GaN nanowires with different In contents could be either separately driven to generate green or blue light or simultaneously biased to generate a broad electroluminescence spectrum.

Reference:
•Xing Dai, Agnes Messanvi, Hezhi Zhang, Christophe Durand, Joël Eymery, Catherine Bougerol, François H Julien, Maria Tchernycheva « Flexible Light-Emitting Diodes Based on Vertical Nitride Nanowires» Nano Letters 15 (10), 6958-6964 (2015).

 

  • Flexible white light emitting diodes based on nitride nanowires and nanophosphors

By doping the polymer matrix with nanophosphors, flexible nanowire-based LEDs were demonstrated. The nanowires were embedded into a phosphor-doped PDMS matrix, peeled off from the growth substrate and contacted using flexible and transparent silver nanowire mesh. Mechanical bending stress down to a curvature radius of 5 mm did not yield any degradation of the LED performance.

References:
•Nan Guan, Xing Dai, Andrey V Babichev, François H Julien, Maria Tchernycheva “Flexible inorganic light emitting diodes based on semiconductor nanowires” Minireview in Chemical Science 8, 7904-7911 (2017).
•Nan Guan, Xing Dai, Agnes Messanvi, Hezhi Zhang, Jianchang Yan, E. Gautier, Catherine Bougerol, François H. Julien, Christophe Durand, Joël Eymery, and Maria Tchernycheva, Flexible White Light Emitting Diodes Based on Nitride Nanowires and Nanophosphors, ACS Photonics 3 (4), 597-603 (2016).

  • InGaN/GaN core-shell single nanowire light emitting diodes with graphene-based p-contact

Single wire LEDs with graphene contacts present a strong interest for fundamental studies as well as for the development of novel photonic platforms combining nanoscale active optical elements on flexible substrates. We demonstrated single nanowire InGaN/GaN core/shell LEDs with a transparent graphene contact for hole injection. Single wire LEDs with graphene contact present efficient electroluminescence starting from 0.16 µA injection current. The electroluminescence changes color from green to blue with increasing injection current. High-resolution cathodoluminescence on cleaved nanowires demonstrates that the blue peak originates from the emission of the radial quantum well on the m-planes, whereas the green peak arises from the In-rich region at the junction between the m-planes and the semipolar planes. The spectral behavior of the electroluminescence is understood by modeling the current distribution within the nanowire.

Reference:
•Tchernycheva M, Lavenus P, Zhang H, Babichev A V, Jacopin G, Shahmohammadi M, Julien F H, Ciechonski R, Vescovi G, Kryliouk O, InGaN/GaN Core/Shell Single Nanowire Light Emitting Diodes with Graphene-Based P-Contact, Nano Letters 14, 2456 (2014).

 

  • Color control of nanowire InGaN/GaN light emitting diodes by post-growth treatment

The complexity of the three dimensional active region of NW LEDs makes the growth control very challenging. It has been observed that in NWs with intrinsic compositional inhomogeneities the electro-luminescence (EL) depends on the contact layout. This dependence of the EL on the contact morphology opens the way to control the LED emission color at the device processing stage. Indeed, if the compositional variation cannot be avoided at the growth stage, the electrical injection in the unwanted regions can be inhibited by a dedicated post-growth treatment.
We have shown that for NW LEDs coming from the same growth run the EL color can be controlled by the contacting procedure. In particular, the pure blue emission without a spectral shift with injected current was achieved with NWs initially presenting regions of different InGaN composition. This was realized by locally reducing the conductivity of the p-doped GaN shell using fluorine plasma treatment to inhibit the electrical injection in the In-rich region of the QW. Modification of the contact layout to selectively contact the lateral m-plane facets and a post-growth CHF3 plasma treatment allowed to suppress the unwanted green contribution at medium and high injection while increasing the EL intensity in the blue spectral range. ICP etching of the In-rich region allowed to suppress the green emission for all injection currents. However an intensity loss in the blue spectral range due to ICP-induced damages was observed. The selective contacting of the m-plane and the plasma treatment of the NW top appear as a promising solution for controlling the color of core/shell NW LED with inhomogeneous internal composition.

Reference:
•Hezhi Zhang, Gwénolé Jacopin, Vladimir Neplokh, Ludovic Largeau, François H. Julien, Olga Kryliouk, Maria Tchernycheva « Color control of nanowire InGaN/GaN light emitting diodes by post-growth treatment» Nanotechnology, 26 465203A (2015).

 

  • Green m-plane InGaN/GAN nanowire LEDs

High EQE green emission is an open challenge for the LED technology. We demonstrated green emission from InGaN/GaN core/shell nanowires using low temperature MOCVD growth of the radial quantum wells. This demonstrates the possibility to produce green emitters with core-shell wire LEDs elaborated by industrially-relevant MOVPE technique.

Reference:
Akanksha Kapoor, Nan Guan, Martin Vallo, Agnès Messanvi, Lorenzo Mancini, Eric Gautier, Catherine Bougerol, Bruno Gayral, François H Julien, François Vurpillot, Lorenzo Rigutti, Maria Tchernycheva, Joel Eymery, Christophe Durand “Green electroluminescence from radial m-plane InGaN quantum wells grown on GaN wire sidewalls by MOVPE” ACS Photonics ASAP 2018

 

  • Integrated photonic platform based on InGaN/GaN nanowire emitters and detectors

There is a growing demand for heterogeneous integration of photonic components with non-photonic elements (such as electronic circuits, micro-electromechanical systems, bio-sensors, etc…) to fabricate compact platforms with different functionalities. Nitride nanowire optical components present an ideal solution to implement this kind of integrated platforms in the visible spectral range.
We fabricated a photonic platform composed of single wire LED and photodetectors optically coupled by waveguides. MOVPE-grown InGaN/GaN p-n junction core-shell nanowires have been used for device fabrication. To achieve a good spectral matching between the emission wavelength and the detection range, different active regions containing either five narrow InGaN/GaN quantum wells or one wide InGaN segment were employed for the LED and detector, respectively. The communication wavelength is 400 nm. The devices are realized by means of electron beam lithography on Si/SiO2 templates and connected by around 100 µm long non-rectilinear SiN waveguides. The photodetector current trace shows signal variation correlated with the LED on/off switching with a fast transition time below 0.5 sec.

References:
M. Tchernycheva, A. Messanvi, A. de Luna Bugallo, G. Jacopin, P. Lavenus, L. Rigutti, H. Zhang, Y. Halioua, F. H. Julien, J. Eymery, C. Durand, “Integrated photonic platform based on InGaN/GaN nanowire emitters and detectors”, Nano Letters 14, 3515 (2014)
•Nan Guan, Andrey Babichev, Martin Foldyna, Dmitry Denisov, François H Julien, Maria Tchernycheva “Optimization of the optical coupling in nanowire-based integrated photonic platforms by FDTD simulation”, Beilstein journal of nanotechnology Volume 9, Issue 1, Pages 2248-2254 (2018).