An AlGaN/GaN HEMT on Si has received significant attention due to the availability of large sized Si substrate at low cost. The limiting factors for high quality GaN/Si are large lattice and thermal expansion-coefficient mismatches between GaN and Si, which lead to high dislocation densities, wafer bowing and crack formation. Therefore, it is imperative to grow high quality GaN/Si with minimum wafer bowing and without crack in order to improve the device performances.
The AlGaN/GaN HEMTs were grown on 8-inch Si substrates using MOCVD technique. The HEMT structure consisted of the high-temperature-grown AlN nucleation layer (HT-AlN NL), the HT-Al0.3Ga0.7N intermediate layer (HT-AlGaN IL), the AlGaN/AlN strained layer superlattice (SLS), the GaN layer and the Al0.26Ga0.74N barrier layer. The HT-AlN NL was effective in avoiding the reaction between Ga and Si, which resulted in the specular surface morphology. The characteristic of the HT-AlN NL affected the vertical breakdown characteristics. The wafer b owing can be minimized by use of SLS and GaN because of counter-balance of thermal and lattice mismatches between SLS and GaN.
The AlGaN/GaN HEMT exhibited a Hall mobility of 1730 cm2/vs, a sheet carrier density of 7.4x1012 cm-2 and the wafer bowing value of 42 um. The vertical voltage at 1 uA/mm was between 950 V and 1000 V across the wafer. The normally-off devices were fabricated by using gate-recess and MOS technology. The devices exhibited good dc characteristics with drain current maximum of 300 mA/mm, threshold voltage of +2.4 V and 3-terminal off-breakdown voltage of 1650 V.
Takashi Egawa, "200-mm GaN/Si technology for power device applications (Conference Presentation)," Proc. SPIE 10104, Gallium Nitride Materials and Devices XII, 101041C (Presented at SPIE OPTO: February 01, 2017; Published: 19 April 2017); https://doi.org/10.1117/12.2250249.5391659250001.
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