In comparison with planar devices, nanowire photodetectors present advantages in terms of miniaturization, speed, and design flexibility. III nitride nanowires are particularly suitable for spectrally-selective UV photodetection, thanks to their band gap energy and their stability against chemical, mechanical or electrical stress. However, their UV photoresponse scales sublinearly with the optical power, which hinders their introduction in applications that require power quantification. Here, we present GaN nanowires containing a single AlN/GaN/AlN heterostructure, whose response is linear with the optical power when their diameter is small enough to ensure a complete depletion of the wire due to surface states.
On the other hand, III-nitride nanowires are also interesting for infrared photodetection using intersubband (ISB) transitions in nanodisks inserted in the wire. We systematically investigated ISB transitions in the near-infrared wavelengths focusing around 1.55 µm in GaN/AlN nanowire heterostructures. Attaining this short wavelength requires small GaN/AlN nanodisks (2 nm / 3 nm). Based on this study, we present the first single-nanowire quantum well infrared photodetector (NW-QWIP), observing photocurrent at 1.55 µm. Finally, we introduce an extension of the study to cover the mid-infrared spectral range, up to around 6 µm, using ISB transitions in GaN/AlGaN nanowires.
Research on III-nitride intersubband (ISB) transitions in the THz spectral range is motivated by the large LO-phonon energy of GaN, which should permit device operation with limited thermal interference, and at infrared wavelengths inaccessible to other III-V compounds due to Reststrahlen absorption. A main challenge to extend the polar GaN-ISB technology towards the THz region comes from the polarization-induced internal electric field, which imposes an additional confinement that increases the energetic distance between the electronic levels. In order to surmount this constraint, we propose alternative multi-layer quantum well designs that create a pseudo-square potential profile with symmetric wavefunctions . The robustness of these designs and their integration in device architectures requiring tunneling transport will be discussed.
An alternative approach to obtain square potential profiles is the use of nonpolar crystallographic orientations. In this contribution, we present an experimental study of THz ISB transitions in m-plane GaN/AlGaN quantum wells grown on free-standing m-GaN . For Al contents below 15%, such structures can be grown without epitaxially-induced extended defects. We demonstrate nonpolar quantum wells which display ISB transitions in the 7-10 THz band, and we will discuss the effect of the doping density in the quantum wells on the transition energy and line width. Finally, we will present a comparative study using silicon and germanium as n-type dopants.
 M. Beeler, et al., Appl. Phys. Lett. 105, 131106 (2014)
 C.B. Lim, et al., Nanotechnology 26, 435201 (2015); Nanotechnology 27, 145201 (2016).