III-nitride nanostructures have recently emerged as promising materials for new intersubband (ISB) devices in a wide variety of applications. These ISB technologies rely on infrared optical transitions between quantum-confined electronic states in the conduction band of GaN/Al(Ga)N nanostructures, namely quantum wells or quantum dots. The large conduction band offset (about 1.8 eV for GaN/AlN) and sub-picosecond ISB relaxation of III-nitrides render them appealing materials for ultrafast photonic devices in near-infrared telecommunication networks. Furthermore, the large energy of GaN longitudinal-optical phonons (92 meV) opens prospects for high-temperature THz quantum cascade lasers and ISB devices covering the 5-10 THz band, inaccessible to As-based technologies due to phonon absorption. In this paper, we describe the basic features of ISB transitions in III-nitride quantum wells and quantum dots, in terms of theoretical calculations, material growth, spectroscopy, resonant transport phenomena, and device implementation. The latest results in the fabrication of control-by-design devices such as all-optical switches, electro-optical modulators, photodetectors, and lasers are also presented.

The strong light-matter coupling regime and lasing in a GaN microcavity fabricated by incorporating a high optical quality GaN membrane inside an all-dielectric mirror cavity is demonstrated at room temperature. A nonlinear increase of the emission and line narrowing marks the onset of polariton lasing regime with significantly reduced threshold compared with previous reports for bulk GaN microcavity. This combination of low lasing thresholds and ease of fabrication allows incorporation of quantum wells and electrical contacts into the active region, paving the way for electrically driven room temperature (RT) polariton laser devices.

Wavelength dependent photochemical etching of GaN films reveals a strong resonant enhancement of the photocurrent at the GaN gap, in close agreement with the excitonic absorption profile of GaN. The corresponding etching rate of GaN strongly correlates with the measured photocurrent. No photocurrent, nor etching is observed for AlGaN films under same excitation conditions. The method could pave the way to the development of truly selective etching of GaN on AlGaN for the fabrication of nitride based optoelectronic devices.