| Indium nitride is a promising channel material for high frequency transistors because of its low effective electron mass (m* = 0.04m0) and high electron velocities. However, realizing practical InN devices has a number of challenges. One of the challenges is the presence of large surface electron accumulation layer. It is caused by InN surface Fermi level pinning above conduction band that results in downward bending of the bands at the surface. It has been reported that chemical surface treatment could un-pin the surface, reducing the electron accumulation density. In this work, hydrochloric acid, ammonium sulfide and trimethylaluminium (TMA) are used for the passivation of InN wafers before dielectric deposition. Metal-oxide-semiconductor capacitor (MOSCAP) structures are fabricated to study the effectiveness of the passivation methods. The current-voltage and capacitance-voltage characteristics are measured on MOSCAPs with atomic layer deposited high-k dielectrics. Current-voltage curves indicate that high-k dielectric layer shows excellent insulating properties with low leakage currents. Measured capacitance-voltage curves demonstrate surface electron accumulation even with passivation. Simulations of device structure are carried out to understand the capacitance-voltage behavior. |
