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 6.13×10¹⁵cm^-2, the carrier mobility drops sharply, while the sheet carrier density remains the same as that of an unirradiated sample. Moreover, even for a fluence of up to 3.66×10¹⁶cm^-2, the sheet carrier density shows only a slight drop. We attribute the degradation of the figure-of-merit (product of n_s×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 n_s×μ of 2DEG during rapid thermal annealing processes at relatively high temperature has been attributed to the activation of Ge_Ga transmuted from Ga and the recovery of displaced defects.