A method for preparing atomically smooth gallium nitride (GaN) surfaces that involves chemical etching with a platinum catalyst in water is presented. The flattened GaN(0001) surface exhibits periodic structures composed of straight-edged steps the height of a single bilayer. Atomic step and terrace structures containing an extremely small number of scratches and pits can be achieved on wafer scale (2 inch diameter). Photoluminescence analysis revealed that the intensity of band-edge luminescence increases significantly after flattening. Low energy electron diffraction indicated that the flattened GaN surface is crystallographically well-ordered. Current density between the wafer and Pt is observed when they are rotated, suggesting that the GaN surface is etched by an electrochemical reaction initiated by the tribo effect between Pt and the wafer surface.

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We used catalyst-referred etching, which is an abrasive-free planarization method, to produce an extremely smooth surface on a 4H-SiC substrate. However, the removal rate was lower than that obtained by chemical mechanical polishing, which is the planarization method generally used for SiC substrates. To improve the removal rate, we investigated its dependence on rotational velocity and processing pressure. We found that the removal rate increases in proportion to both rotational velocity and processing pressure. A lapped 4H-SiC substrate was planarized under conditions that achieved the highest removal rate of approximately 500 nm/h. A smooth surface with a root-mean square roughness of less than 0.1 nm was fabricated within 15 min. Because the surface, which was processed under conditions of high rotational velocity and high processing pressure, consisted of a step–terrace structure, it was well ordered up to the topmost surface.

Catalyst-referred etching (CARE) is a novel abrasive-free planarization method. CARE-processed 4H-SiC(0001) surfaces are extremely flat and undamaged over the whole wafer. They consist of single-bilayer-height atomic steps and atomically flat terraces. This suggests that the etching properties depend principally on the atomic-step density of the substrate surface. We used on-axis and 8 degrees off-axis substrates to investigate the processing characteristics that affect the atomic-step density of these substrates. We found a strong correlation between the removal rate and the atomic-step density of the two substrates. For the on-axis substrate, the removal rate increased with increasing surface roughness, which increases with an increasing atomic-step density. The removal rate ratio is approximately the same as the atomic-step density ratio of the two substrates.

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