Thanks to their large conduction band offset (up to 1.75 eV for GaN/AlN), III-nitride nanostructures in the form of quantum dots (QD) or quantum wells (QW) offer great prospects for ultrafast intersubband devices operating at room temperature in the near-infrared spectral range. Nitride intersubband devices are intrinsically very fast because of the subpicosecond absorption recovery time due to enhanced electron-LO phonon interaction in these highly ionic materials. In this talk, we will report on recent achievements in terms of GaN/AlGaN-based intersubband physics, devices and technology. 

As a first example of QW intersubband device, we will show how electron tunneling between coupled quantum wells can be applied to the fabrication of fast electro-optical modulators at 1.3-1.55 µm wavelengths. Then, we will present recent experiments on a new type of ultrafast detectors based on the quantum cascade concept. Finally, we will discuss the progress towards near-infrared lasers and amplifiers based on the observation of intersubband light emission from GaN/AlN quantum wells at a wavelength as short as 2 µm.  

GaN/AlN QDs are also of great interest for intersubband devices, namely because of the achievable large QD density (a few 10¹² cm^-2) and of the expected narrow linewidth of intraband transitions due to the slow-down of the dephasing mechanisms. We will describe recent resonant Raman scattering experiments which reveal an intraband light emission at a record short wavelength of 1.5 µm and allow estimating the intraband linewidth of single QDs. We have also performed pump-probe femtosecond measurements which show the extremely short intraband lifetime (165 fs) while the intraband saturation intensity (0.27 pJ/µm²) is one order of magnitude smaller than that measured in QWs. These results open prospects for ultrafast saturable absorbers and all-optical switches based on GaN QDs for telecommunication applications.

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1. Plasma-Assisted MBE of III-nitride semiconductors: From two-dimensional layers to nanostructures
2. Morphological, structural and optical properties of high-quality InN on GaN-template films deposited by RF sputtering
3. The microstructure and properties of InN layers
4. Non-linear absorption measurements of InN/InGaN multiple-quantum-wells structures at 1.5 µm using the Z-Scan method
5. Interfacial structure of semipolar AlN grown on m-plane sapphire by PAMBE
6. Structural models of GaN quantum dots in semipolar AlN