Neutron irradiation effect in two-dimensional electron gas of AlGaN/GaN heterostructures

AlGaN/GaN heterostructures have been irradiated by neutrons with different fluences and characterized by means of temperature-dependent Hall measurements and Micro-Raman scattering techniques. It is found that the carrier mobility of two-dimensional electron gas (2DEG) is very sensitive to neutrons. At a low fluence of 6.13 x 1015 cm-2, the carrier mobility drops sharply, while the sheet carrier density remains the same as that of a unirradiated sample. Moreover, even for a fluence of up to 3.66 x 1016 cm-2, the sheet carrier density shows only a slight drop. We attribute the degradation of the figure-of-merit (product of ns x μ) of 2DEG to the defects induced by neutron irradiation. Raman measurements show that neutron irradiation does not yield obvious change to the strain state of AlGaN/GaN heterostructures, which proves that degradation of sheet carrier density has no relation to strain relaxation in the present study. The increase of the product of ns x μ of 2DEG during rapid thermal annealing processes at relatively high temperature has been attributed to the activation of GeGa transmuted from Ga and the recovery of displaced defects. (authors)