Intersubband device applications of nitride quantum structures

Nitride semiconductor quantum structures feature some unique properties for intersubband device development, including a record large conduction-band offset that allows extending the operating wavelength to the near-infrared spectral region, and large optical phonon energies that are advantageous for the development of THz devices. In this paper we review our recent work aimed at the demonstration of novel intersubband device functionalities using these materials. In particular, we have developed ultrafast all-optical switching devices operating at fiber-optic communication wavelengths, based on intersubband cross-absorption saturation in GaN/AlN quantum-well waveguides. Strong self-phase modulation of ultrafast optical pulses has also been measured in these waveguides, revealing a large intersubband refractive-index nonlinearity which is also promising for all-optical switching applications. Furthermore, we have demonstrated optically pumped intersubband light emission from GaN/AlN quantum wells at the record short wavelength of about 2 μm. Finally, we have used a rigorous Monte Carlo model to show that GaN/AlGaN quantum wells are promising for the development of THz quantum cascade lasers capable in principle of operation without cryogenic cooling.