Trouble with Estimating GaN Screw Dislocation Density

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SUMMARY

The forum discussion centers on estimating screw dislocation density in GaN samples using XRD measurements. The user initially calculated the Full Width at Half Maximum (FWHM) incorrectly in radians, resulting in an erroneous dislocation density value. A correction was provided, indicating that the correct conversion from degrees to radians should yield approximately 0.023562 radians. The accurate formula for screw dislocation density is nstd = FWHM²/(4.35 * bs²), where the Burger vector must be converted to centimeters, leading to a calculated density of approximately 5·1010 cm-2.

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  • Understanding of X-ray Diffraction (XRD) techniques
  • Knowledge of Full Width at Half Maximum (FWHM) calculations
  • Familiarity with dislocation density formulas in semiconductor physics
  • Ability to convert units, specifically from nanometers to centimeters
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  • Research the impact of screw dislocation density on GaN material properties
  • Learn about advanced XRD techniques for characterizing semiconductor materials
  • Study the significance of the Burger vector in dislocation density calculations
  • Explore methods to improve the quality of GaN samples in fabrication
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This discussion is beneficial for materials scientists, semiconductor researchers, and anyone involved in the characterization of GaN materials, particularly those focused on dislocation density analysis and XRD techniques.

gabby1981
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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?
 
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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 nstd is equal to the following (your formula is incomplete; also one needs to convert Burger vector bs to centimeters to get dislocation density in cm-2):

nstd = FWHM2/(4.35*bs2)=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.
 

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