Wafer averages for sheet resistivity vs 1-μm absorption loss for initial GaN HEMT films grown on 3-in. sapphire substrates.
Bubble plot with 19 1-μm absorption measurements across a 3-in. GaN HEMT/sapphire wafer that was rotated during growth. The center of the wafer is with the vertical and horizontal displacements at 0 mm. The wafer average absorption is 0.08% with a standard deviation of ±0.02%. The sheet resistance of the wafer was 304 Ω/sq with a standard deviation of 1.6%.
Charge-depth profile for a GaN HEMT with 4.2% absorption.
Absorption measurements at different steps of epi removal for three GaN HEMT/sapphire wafers exhibiting significantly different starting absorptions. The wafers were first etched 1500 Å removing the AlGaN layer and top of the GaN buffer, then another 7000 Å of the GaN buffer was removed, and finally the rest of the epi was ground and polished off leaving the sapphire substrate.
Oxygen and aluminum SIMS depth profiles for a GaN HEMT/sapphire sample with 4.2% absorption and a sample with 0.1% absorption. The aluminum profile identifies the location of the AlN nucleation layer on the sapphire substrate. The AlN thickness is exaggerated due to its slow sputter rate.
Wafer averages for sheet resistivity vs absorption loss at 1 μm for GaN HEMT films grown on 100-mm sapphire substrates using a two-step method for AlN growth.
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