Effects of irradiation of 290 MeV U-ions in GaN epi-layers

In the present work, the resistivity, mobility and the carrier density at either room temperature or 77 K in 3-μm-thick n-GaN epi-layers irradiated with 290 MeV 238U32+ ions were tested with Hall measurements. It is found that the carrier mobility at 77 K is lower than that at room temperature in the specimens irradiated to fluences of the 1 × 109 and 1 × 1010 ions/cm2, showing a behavior different from the pristine specimen. The carrier density increases with ion fluence, and is above the dopant concentration when the ion fluence reaches 5 × 1010 ions/cm2. Moreover, the ionized impurity scattering plays a dominant role in the Hall effect after irradiation. A decrease of the ionized impurities due to the recombination of Ga vacancies (VGa-3) and the Ga interstitials (Ga(I)) was observed. The irradiation to the fluence of 5 × 1010 ions/cm2 produced N vacancies, which act as a kind of donor making the carrier density increase. The Raman spectra show that the E2 (high) mode shifts to a higher frequency meanwhile the FWTH increases after the irradiation, indicating there is an increase of strain in the irradiated GaN epi-layers. A consistency between the Raman spectra and the HRXRD spectra was found.