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GaN-based structures are promising for production of radiation detectors and high-voltage high-frequency devices. Particle detectors made of GaN are beneficial as devices simultaneously generating of the optical and electrical signals. Photon-electron coupling cross-section is a parameter which relates radiation absorption and emission characteristics. On the other hand, photon-electron coupling cross-section together with photo-ionization energy are fingerprints of deep centres in material. In this work, the wafer fragments of the GaN grown by ammonothermal (AT) technology are studied to reveal the dominant defects introduced by growth procedures and reactor neutron irradiations in a wide range, 10¹²–10¹⁶ cm⁻², of fluences. Several defects in the as-grown and irradiated material have been revealed by using the pulsed photo-ionization spectroscopy (PPIS) technique. The PPIS measurements were performed by combining femtosecond (40 fs) and nanosecond (4 ns) laser pulses emitted by optical parametric oscillators (OPO) to clarify the role of electron-phonon coupling. Variations of the operational characteristics of the tentative sensors, made of the AT GaN doped with Mg and Mn, under radiation damage by reactor neutrons have been considered.

Multi-photon ionization (MPI) spectroscopy of solid surfaces under ambient conditions and in nitrogen has been established and exemplified for a variety of materials. This was accomplished using a dedicated experimental setup that monitors the photoelectron yield as a function of the laser wavelength. The MPI spectra resemble the absorption characteristics, however, possess more peaks and are more detailed. This demonstrated the possibility to apply MPI spectroscopy for fast analysis of solids. The dependence of the signals upon the laser flux implies that the ionization mechanism depends on the examined molecule and in many cases it is a two-step process, via a long-living intermediate energy state. The method provides quantification in the pmole range and allows for surface imaging.