II-nitride materials have demonstrated excellent properties for radiation detection. One of the main advantages is their tunable bandgap edge within a wide range from the UV to the IR region by using AlGaN and InGaN ternary alloys. Their wide bandgap allows us to predict low dark currents and noise and makes them adequate for operation at high temperatures and harsh environments. Low-dimensional structures can be fabricated from bottom-up technologies through the self-assembled growth or by using nanotechnology tools to enhance quantum confinement. Control of piezoelectricity and polarization fields is a nitride property that, exploited in a proper way, leads to obtain internal gain mechanisms at low voltages.

In this work, on one hand, InGaN/GaN MQW photodetectors are presented as a reliable alternative to accomplish selective detection in the UVA and visible ranges.1 Back-illumination helps to reduce optical losses and to integrate optical filtering with rejection ratios of 2-4 orders of magnitude. Peak responsivities higher than 1012 W-1Hz1/2cm were achieved. P-InGaN/GaN-N photodetectors were fabricated to exploit these characteristics in combustion monitoring2 or fluorescence spectroscopy. Specific MQW structures were designed by internal field engineering and fabricated to study gain mechanisms.

On the other hand, detection of high-energy photons was assessed by characterization of GaN MSM and SB photodiodes under synchrotron radiation.3 Carrier thermalization and scattering by ionization and phonon emission have been modelled from probabilistic methods and related to the experimental results. The importance of the layer thickness and material quality for high energy radiation will be discussed. Besides, performance of GaN detectors grown by HVPE (452-µm thick) and nano-ELO (10-µm thick) material were compared under alpha-particle irradiation. HVPE MIS devices were fabricated by photoelectrochemical oxidation of the surface and SiN deposition before evaporation of Au semitransparent contact. This procedure reduced the leakage current notoriously in the devices studied. Samples grown by HVPE showed a higher total energy deposition as expected from the larger volume but a less uniform response caused by material inhomogeneities.

1 C. Rivera, J. L. Pau, A. Navarro, and E. Muñoz, “Photoresponse of (In,Ga)N-GaN Multiple-Quantum-Well Structures in the Visible and UVA Ranges,” IEEE J. Quantum Electron. 42, 51 (2006).

2 J. L. Pau, J. Anduaga, C. Rivera, Á. Navarro, I. Álava, M. Redondo, and E. Muñoz, "Optical sensors based on III-nitride photodetectors for flame sensing and combustion monitoring," Appl. Opt. 45, 7498 (2006).

3 J. L. Pau, C. Rivera, E. Muñoz, E. Calleja, U. Schühle, E. Frayssinet, B. Beaumont, J. P. Faurie, and P. Gibart, “Response of ultra-low dislocation density GaN photodetectors in the near- and vacuum-ultraviolet,” J. Appl. Phys., 95, 8275 (2004).