Degradation mechanisms of optoelectric properties of GaN via highly-charged 209Bi33+ ions irradiation

• Published in: Applied surface science Vol. 440; pp. 814 - 820
• Main Authors: Zhang, L.Q., Zhang, C.H., Xian, Y.Q., Liu, J., Ding, Z.N., Yan, T.X., Chen, Y.G., Su, C.H., Li, J.Y., Liu, H.P.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.05.2018
• Subjects: GaN; Highly-charged bismuth-ion irradiation; Optoelectric properties; Raman spectrum; Varying temperature photoluminescence (PL) spectrum; Highly-charged bismuth-ion irradiation; Optoelectric properties; Varying temperature photoluminescence (PL) spectrum; GaN; Raman spectrum
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2018.01.170

•GaN epi-layers were irradiated with 209Bi33+ ions to various fluences.•Electrical properties were extracted from Raman spectra.•Variable temperature photoluminescence (PL) spectra were measured from 3 K to 300 K.•Vacancy-type defects lead to a drastic degradation in electrical transports.•Photoluminescence lines’ features and emission mechanisms were analyzed in detail. N-type gallium nitride (GaN) epitaxial layers were subjected to 990-keV Bi33+ ions irradiation to various fluences. Optoelectric properties of the irradiated-GaN specimens were studied by means of Raman scattering and variable temperature photoluminescence (PL) spectroscopy. Raman spectra reveal that both the free-carrier concentration and its mobility generally decrease with a successive increase in ion fluence. Electro-optic mechanisms dominated the electrical transport to a fluence of 1.061 × 1012 Bi33+/cm2. Above this fluence, electrical properties were governed by the deformation potential. The appearance of vacancy-type defects results in an abrupt degradation in electrical transports. Varying temperature photoluminescence (PL) spectra display that all emission lines of 1.061 × 1012 Bi33+/cm2-irradiated specimen present a general remarkable thermal redshift, quenching, and broadening, including donor-bound-exciton peak, yellow luminescence band, and LO-phonon replicas. Moreover, as the temperature rises, a transformation from excitons (donor-acceptor pairs’ luminescence) to band-to-band transitions (donor-acceptor combinations) was found, and the shrinkage effect of the band gap dominated the shift of the peak position gradually, especially the temperature increases above 150 K. In contrast to the un-irradiated specimen, a sensitive temperature dependence of all photoluminescence (PL) lines’ intensity obtained from 1.061 × 1012 Bi33+/cm2-irradiated specimen was found. Mechanisms underlying were discussed.