The full InGaN structure is used to achieve red light emitting diodes (LEDs). This LED structure is composed of a partly relaxed InGaN pseudo-substrate fabricated by Soitec, namely InGaNOS, a ndoped buffer layer formed by a set of In x Ga 1-x N/GaN superlattices, thin In y Ga 1-y N/In x Ga 1-x N multiple quantum wells, and a p doped In x Ga 1-x N area. p-doped InGaN layers are first studied to determine the optimal Mg concentration. In the case of an In content of 2%, an acceptor concentration of 1x10 19 /cm 3 was measured for a Mg concentration of 2x10 19 /cm 3 . Red electroluminescence was then demonstrated for two generations of LEDs, including chip sizes of 300x300 and 50x50 µm². The differences between these two LED generations are detailed. For both devices, red emission with a peak wavelength at 620 nm was observed for a pumping current density of 12 A/cm². Red light-emission is maintained over the entire tested current range. From the first to the second LED generation, the maximum external quantum efficiency, obtained in the range of 17 to 40 A/cm², was increased by almost one order of magnitude (factor 9) thanks to the different optimizations.

Engineering nonlinear optical responses at the microscale is a key topic in photonics for achieving efficient frequency conversion and light manipulation. Gallium nitride (GaN) is a promising semiconductor material for integrated nonlinear photonic structures. In this work, we use epitaxially grown GaN microwires as nonlinear optical whispering gallery and Fabry-Perot resonators. We demonstrate an effective generation of second-harmonic and polarizationdependent signals of whispering gallery and Fabry-Perot modes under near-infrared excitation. We show how the rotation of the excitation polarization can be used to control and switch between Fabry-Perot and whispering gallery modes in tapered GaN microwire resonators. We demonstrate the enhancement of two-photon luminescence in the yellow-green spectral range due to efficient coupling between whispering gallery, Fabry-Perot modes, and excitonic states in GaN. This luminescence enhancement allows us to conveniently visualize whispering gallery modes excited with a near-infrared source. Such microwire resonators can be used as compact microlasers or sensing elements in photonic sensors.

In this work non-scanning far-field nonlinear optical microscopy is employed to study the whispering gallery modes in tapered GaN microwire resonators. We demonstrate the confinement of whispering gallery modes under near-infrared excitation with the photon energy close to half of GaN bandgap. Our results indicate the enhancement of yellow-green luminescence by whispering gallery modes in GaN microwires.