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Gallium nitride (GaN) high-electron-mobility transistor (HEMT) and vertical GaN metal-oxide-semiconductor (MOS) devices have potential application to high power and high frequency because of their superior characteristics, such as wide band gap (B g ), high electron saturation velocity, and a high critical breakdown voltage [ 1 – 3 ]. Gate insulator plays an important role to suppress the leakage current in both GaN HEMT and GaN MOS devices. Various materials such as SiO 2 , Al 2 O 3 , HfO 2 , AlSiO x , and HfSiO x have been widely investigated as gate insulator, and films of these materials are typically deposited via chemical vapor deposition or atomic layer deposition (ALD) [ 4 – 10 ]. Figure 1 shows the relationship between dielectric constant ( k ) and B g of candidate gate insulators [11] . The B g generally decreases as the k value increases. HfO 2 is known to have a high k value but crystallization temperature is as low as 400°C. Al 2 O 3 starts to crystalize around 700°C. On the other hand, silicate materials such as AlSiO x and HfSiO x have a more stable amorphous structure at 800°C and expect to suppress the leakage current. Here, AlSiO x and HfSiO x films were formed by a two-step process such as film formation of (Al 2 O 3 ) m /(SiO 2 ) n and (HfO 2 ) m /(SiO 2 ) n nanolaminate structures using ALD, respectively, and post-deposition annealing (PDA) treatment. |
