Trouble with Estimating GaN Screw Dislocation Density

[gabby1981]

Hi everyone.

Recently, I did (002) XRD scanning to get the rocking curve of a sample of GaN. From the measurement, I found that the FWHM of the sample is ~1.35 degree. I tried to convert it into radian unit using this formula: angle in radian=angle in degree x π /180 (degree). I got the answer around 4.74 radian. Then I used this value to estimate the screw dislocation density of the sample using this formula; screw dislocation density = FWHM²/4.35 x burger vector (0.5185). The answer is far off the reasonable value that typically reported for GaN. Could anyone help me?

 

[zvz]

1.35° = 3.14159 Rad.*1.35°/180° = 0.023562 Rad. not 4.74 (you forgot to divide by 180, I presume). The screw-type dislocation density n_std is equal to the following (your formula is incomplete; also one needs to convert Burger vector b_s to centimeters to get dislocation density in cm^-2):

n_std = FWHM²/(4.35*b_s²)=0.023562²/(4.35*(0.5185 nm*10^-7 cm/nm)²) ≈ 5·10¹⁰ cm^-2

It is a quite poor quality material, which is expected from the very broad XRD ω-scan.