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Evaluation of the crystallinity (tilt and twist distributions) of a GaN thin film by the X-ray rocking curve method


In recent years, nitride materials of the third element group centering on GaN have gotten a lot of attention, stimulating the developments of blue to ultraviolet light-emitting and power devices. The characteristics of these devices have a close relationship with the crystallinity of the thin film formed on each device. The X-ray rocking curve method is one way to evaluating crystallinity.

For the GaN thin film formed on a sapphire substrate, the distributions of its tilt (the tilt angle of the crystal axis) and twist (the rotation angle of the crystal axis) are evaluated by means of the rocking curve method (using the scan with incident angle ω and the scan with in-plane rotation angle φ).

In the 2 μm thick GaN thin film formed on a sapphire (0001) substrate, its tilt distribution and its twist distribution are evaluated using the GaN (0002) rocking curve (ω scan) and the GaN (1010) rocking curve (φ scan), respectively.


The following shows the geometry of Rigaku SmartLab multipurpose diffractometer's goniometer when measuring each rocking curve and the measurement result of the rocking curve by each lattice plane.










From the values of full width of half maximum (FWHM) of the GaN (0002) and GaN (1010) rocking curves, the tilt distribution and the twist distribution of the GaN crystal are estimated as 0.06° (216 arcsec) and 0.14° (507 arcsec), respectively.

In addition, this measurement employed the horizontal sample mount θ-θ goniometer with an in-plane arm. This goniometer enable the user to keep the sample in the horizontal state when measuring both tilt distribution and twist distribution, so the user can easily measure the sample without worrying about dropping it off.