Double Gaussian Distribution of Barrier Heights, Interface States, and Current Transport Mechanisms in Au/Bi_0.5Na_0.5TiO₃-BaTiO₃/n-GaN MIS Structure

The electrical properties of Au/Bi_0.5Na_0.5TiO₃(BNT)-BaTiO₃(BT)/n-GaN metal–insulator–semiconductor (MIS) structures have been investigated in the temperature range from 120 K to 420 K by current–voltage and capacitance–voltage methods. The Au/BNT-BT/n-GaN MIS structures demonstrate nonideal behaviors indicating the presence of a nonuniform distribution of interface states. Experimental results revealed that the barrier height (Φ_bo), ideality factor (n), and interface state density (N_ss) of the Au/BNT-BT/n-GaN MIS structures are strongly temperature dependent. It is found that N_ss decreases with an increase in temperature. Further, it is observed that Φ_bo increases and n decreases with increasing temperature, which is attributed to barrier inhomogeneities by assuming a Gaussian distribution (GD) of barrier heights (BHs) at the interface. The temperature-dependent I–V characteristics of the Au/BNT-BT/n-GaN MIS structures demonstrate the presence of a double GD having mean BHs of 1.07 eV and 1.91 V and standard deviations of 0.118 V and 0.214 V. Moreover, the inhomogeneous BH is found to be correlated with N_ss, because Φ_bo becomes smaller with increasing N_ss. This indicates that the lateral inhomogeneity of the BH is connected to the nonuniform distribution of the density of states at the interface. Further, the conduction mechanism dominating the reverse-bias leakage current in the MIS structure is investigated.