Free standing GaN wafers have recently been unveiled by Eta Research. These GaN wafers is available for laser diode manufacturers, with the sizes of 2 inches and 4 inches, with conductivity available in either Si-doped n-type or C-doped semi-insulating.
Eta claims that GaN wafers have been engineered to meet the requirements for laser diode manufacturers in a number of ways.
The wafer orientation flat must be closely aligned to the GaN m-plane since lasers may be manufactured by cleaving on the crystallographic plane. Eta has developed the process to achieve 0.0 ± 0.1 inches alignment of the orientation flat to the crystallographic plane.
Typical XRD rocking curve FWHM for both (002) and (102) are in the range of 40 to 50 arcsec. The dislocation density was measured by both CL and etch pit methods, and was found to be in the range of 5E5 to 9E5 /cm2.
Eta’s standard offcut is 0.5 inches toward the m-direction and 0.0 inches toward the a-direction at the center point of the wafer. The center point offcut can be customized in the range of 0.2 inches to 0.6 inches.
The lattice radius specification is > 10 m, and typical values range from 20 m to 60 m with the shape as concave. The offcut variation can be calculated from the lattice radius. However, since there is a small concave wafer bow, the actual offcut variation is less than would be calculated from the lattice radius. The offcut was measure by XRD with x-ray reflection alignment to the real wafer surface. The offcut variation over a 4 inches wafer was measured as 0.06 inches for both the m-direction offcut and a-direction offcut. For example, the m-direction offcut was 0.47 inches on one edge and 0.53 inches on the other edge over the entire 100 mm of the wafer.
The Ga-face is polished to an average roughness of 0.15 nm measured by a 10 µm x 10 µm AFM scan. The wafer is cleaned in a special process to remove any contamination from the polishing procedure. Removal of trace metal impurities from the surface was confirmed by TXRF.
The backside finish is available in either polished or etched. The average roughness of the backside surface measured by 3D profiler over 239 µm x 318 µm is 1 nm for polished and 1 µm for etched.