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Commercially available inorganic white light emitting diodes (LEDs) are essentially based on the combination of a blue InGaN based LED chip covered by a long wavelength emitting (yellow, red) phosphor. We propose to avoid this step of phosphor deposition by taking advantage of the fact that yellow to red emission can be achieved using InGaN alloys. By stacking an InGaN/GaN multiple quantum well (QW) emitting in the yellow, acting as a light converter, and a short wavelength blue-violet pump LED grown on top, white light emission can be obtained. Furthermore, if we extend the emission spectrum of the light converter into the red, a warm white light color is demonstrated when a pump LED is grown on top. However, the high In content InGaN QWs of the light converter have a low thermal stability and the QW efficiency tends to degrade during the growth of the pump LED. Three different solutions are explored to avoid the thermal degradation of the light converter. The monolithic LED structures were grown by molecular beam epitaxy (MBE), by a combination of both MBE and metal-organic chemical vapor phase epitaxy (MOCVD), or by a low temperature full-MOCVD process. The best results are obtained using a complete MOCVD growth process. The structure and the MOCVD growth conditions are specifically adapted in order to avoid the thermal degradation of the large In composition InGaN QWs emitting at long wavelength during the growth of the subsequent layers.

Emission of terahertz (THz) radiations from interdigitated GaN quantum-wells structures under DC-bias has been measured at room temperature. This measurements has been performed by a 4K Si-Bolometer associated with a Fourier Transform Spectrometer. Using an analytical model, we have shown that the observed peak at approximately 3 THz due to 2D ungated plasma-waves oscillations in the quantum well, is emitted by the metallic contacts of our device acting as antennas.

The potential of GaN for X-ray detection in the range from 5 to 40 keV has been assessed. The absorption coefficient has been measured as a fonction of photon energy. Various detectors have been fabricated including MSM and Schottky diodes. They were tested under polychromatic X-ray illumination and under monochromatic irradiation from 6 to 22 keV in the Soleil synchrotron facility. The vertical Schottky diodes perform better as their geometry is better suited to the thick layers required by the low absorption coefficient. The operation mode is discussed in terms of photoconductive and photovoltaic behaviors. Some parasitic effects related to the electrical activation of defects by high energy photons and to the tunnel effect in lightly doped Schottky diodes have been evidenced. These effects disappear in diodes where the doping profile has been optimized. The spectral response is found to be very consistent with the spectral absorption coefficient. The sensitivity of GaN Schottky diodes is evaluated and found to be on the order of 40 photons per second. The response is fast nd linear.

We report on measurements of radiation transmission in the 0.220-0.325 THz and 0.75-1.1 THz frequency ranges through GaN quantum wells grown on sapphire substrates at nitrogen and room temperatures. Significant enhancement of the transmitted beam intensity with applied voltage is found at nitrogen temperature. This effect is explained by changes in the mobility of two-dimensional electrons under electric bias. We have clarified which physical mechanism modifies the electron mobility and we suggest that the effect of voltage-controlled sub-terahertz transmission can be used for the development of electro-optic modulators operating in the sub-THz frequency range.