Recently, a well-known nitride group of University California at Santa Barbara(UCSB)* published an interesting result from measuring the radius of curvature and the threading dislocation density of the commercial 2” GaN-substrates from four major fabrication companies, including Nanowin. Those two parameters indicate the film quality and Nanowin reached 8.08 m of radius of curvature and 4.16x10⁵ cm^-2, a comparably good score there.

This demonstrated that the film curvature is consistent with a compressive to tensile stress gradient (bottom to top) present in the substrates. The origin of the stress gradient and the curvature is attributed to the correlated inclination of edge threading dislocation (TD) lines away from the [0001] direction. That means the substrates with higher threading dislocation densities have smaller radii of curvature.To reduce the dislocation density is the key issue to obtain a higher quality of GaN film. As known, the threading dislocations in GaN film are electrically active and the dense dislocations have substantial impact on not only the carrier transport in emission, but also the lifetime of the on-top-grown devices.

The UCSB work encourages us to concentrate on the way to reduce the film dislocations in order to produce higher quality GaN substrates in future. Currently we have made progresses on further reducing the dislocation density to 10⁴cm^-2 now. Accordingly, the curvature issue is also further improved, more suitable for low-tensile heteroepitaxial device growth. We, therefore, have confidence to keep our GaN substrates remain in the leading position in the world.

 This work was published on Applied Physics Letter, the most popular journal to semiconductor scientists. The UCSB group is of the Center for Solid State Lighting & Energy Electronics.