Neutron irradiation-induced modification of electrical and structural properties of GaN epifilms grown on Al_2O_3 (0001) substrate

摘要

The effects of fast neutron (up to 1.75 x 10(20) f.n. cm(-2) ) and fast plus thermal neutron (up to 3.5 x 10(20) f.t.n. cm(-2) ) irradiation on the electrical properties and crystal lattice of GaN films have been studied. It is shown that high-dose neutron irradiation induces a transition of n-type samples into a semi-insulating state with resistivity of similar to 10(10)Omega cm at room temperature, while p-type films undergo transition to a high-resistance state. The subsequent irradiation of the samples leads to a decrease of resistivity to -10(5)Omega cm at the final neutron fluence. Raman spectra show appearance of the disorder-activated Raman scattering modes at 210, 300 and 670 cm(-1) linked to defects in Ga and N sublattices. X-ray diffraction measurements reveal an expansion of the GaN c-lattice parameter up to a saturation level of 0.42% at the final fluence, while the a-lattice parameter remains nearly unchanged. The initial value of c restores at 1000 degrees C annealing temperature, with the main annealing stage at 150 degrees C-400 degrees C. The significant role of thermal neutrons (E = 0.1 MeV) in the damage build-up in GaN is shown.