Abstract
In this study, titanium nitride (TiN) is synthesized using reactive sputtering for a self-aligned gate process. The Schottky barrier height of the TiN on n-GaN is around 0.5 to 0.6 eV and remains virtually constant with varying nitrogen ratios. As compared with the conventional Ni electrode, the TiN electrode presents a lower turn-on voltage, while its reverse leakage current is comparable with that of Ni. The results of annealing evaluation at different temperatures and duration times show that the TiN/W/Au gate stack can withstand the ohmic annealing process at 800°C for 1 or 3 min. Finally, the self-aligned TiN-gated AlGaN/GaN heterostructure field-effect transistors are obtained with good pinch-off characteristics.
Highlights
The AlGaN/GaN heterostructure field-effect transistors (HFETs) are excellent candidates for high-power and high-frequency electronic devices [1,2]
The typical atomic force microscope (AFM) images of the titanium nitride (TiN) samples were recorded in tapping mode in an area of 20 × 20 μm2 (Figure 1)
These results show that all of the TiN films are Ti-rich with similar actual nitrogen contents, except that the sample grown with 5% N2 has a slightly lower actual nitrogen content than the rest
Summary
The AlGaN/GaN heterostructure field-effect transistors (HFETs) are excellent candidates for high-power and high-frequency electronic devices [1,2]. To achieve a high-temperature performance, it is very desirable to produce a gate contact with a large Schottky barrier height (SBH) and an excellent thermal stability. A self-aligned gate (SAG) process is proposed to minimize the source-to-gate and drainto-gate distances for smaller access resistance, in which a T-shaped Schottky gate is fabricated first and used as a mask directly for ohmic metal evaporation. The Schottky gate and the ohmic electrodes are annealed simultaneously to obtain ohmic contacts [3]. An important technology to form the SAG structure is the Schottky gate which can withstand the ohmic annealing process, because the optimized ohmic contact annealing temperature of the Ti-based multilayers on GaN-based materials is usually around 800°C to 850°C [4,5]. The Schottky gate must be able to withstand such a high temperature during the source-drain ohmic contact annealing process
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