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We first report on the thermal stability and electrical properties of 5 nm-thick TaN films prepared by atomic layer deposition (ALD) using pentakis(ethylmethylamino)tantalum (PEMAT) and ammonia. The deposition rate of the ALD-TaN process was about ∼0.067 nm per cycle in a temperature range between 200 and 250 °C, which is a typical feature of ALD process. In cross sectional transmission electron microscopy (TEM) images, the deposited TaN films exhibited a very smooth and uniform interface. The thermal stabilities of these films were tested by depositing a Cu film of 200 nm thickness on a TaN layer and subsequently performing annealing for 30 min by varying the temperature from 300 to 800 °C in N2 ambient. The high and low-frequency capacitance–voltage (C–V) and breakdown characteristics of a Cu/TaN/SiO2/Si capacitor showed that the barrier properties of thin TaN films against Cu diffusion are inhibited above 500 °C, which is considerably lower than the inhibition temperature estimated by four-point probe or X-ray diffraction (XRD) measurement.

A normally-off GaN-based metal–oxide–semiconductor field effect transistor (MOSFET) was fabricated using the Al0.3Ga0.7N/GaN heterostructure with a two-dimensional electron gas (2DEG) density of ∼1×1014 cm-2 grown on a silicon substrate. The AlGaN layer in the gate region was fully recessed and the whole surface of the device was covered with a high-quality plasma-assisted atomic-layer-deposited (PAALD) Al2O3 layer, which plays the role of not only a gate insulator in the recessed gate region, but also a surface passivation layer in the ungated region between the source and the drain. The fabricated Al2O3/GaN MOSFET exhibited excellent device properties, such as a threshold voltage of 1.1 V extrapolated in the linear region at a drain voltage of 0.1 V, maximum drain current of 353 mA/mm, field-effect mobility of 225 cm2·V-1·s-1, and on-resistance of 9.7 Ω·mm, which are among the best values ever reported for GaN MOSFETs fabricated on silicon substrates.

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