Investigation of Trap States in AlInN/AlN/GaN Heterostructures by Frequency-Dependent Admittance Analysis

Abstract

We present a systematic study on the admittance characterization of surface trap states in unpassivated and SiN x -passivated Al0.83In0.17N/AlN/GaN heterostructures. C–V and G/ω–V measurements were carried out in the frequency range of 1 kHz to 1 MHz, and an equivalent circuit model was used to analyze the experimental data. A detailed analysis of the frequency-dependent capacitance and conductance data was performed, assuming models in which traps are located at the metal–AlInN surface. The density (D t) and time constant (τ t) of the surface trap states have been determined as a function of energy separation from the conduction-band edge (E c − E t). The D st and τ st values of the surface trap states for the unpassivated samples were found to be $$ D_{\rm{st}} \cong (4 - 13) \times 10^{12} $$ $$ {\hbox{eV}}^{ - 1} {\hbox{cm}}^{ - 2} $$ and τ st ≈ 3 μs to 7 μs, respectively. For the passivated sample, D st decreased to $$ 1.5 \times 10^{12} $$ $$ {\hbox{eV}}^{ - 1} {\hbox{cm}}^{ - 2} $$ and τ st to 1.8 μs to 2 μs. The density of surface trap states in Al0.83In0.17N/AlN/GaN heterostructures decreased by approximately one order of magnitude with SiN x passivation, indicating that the SiN x insulator layer between the metal contact and the surface of the Al0.83In0.17N layer can passivate surface states.