I have recently analyse a InGaN/GaN MQW grown by MOCVD on sapphire substrate. The HRXRD results of omega rocking curves yields the FWHMs of (0002) for GaN were broader than the FWHM of (10-15). This is inconsistent with the typical result of GaN in the literature. Usually the (0 0 0 2) FWHM of GaN is much narrower than (10-15), can anyone help me the reason behind broader FWHM of (0002) plane compared to (10-15) with references.
Hi ganesh
Hope you are fine.
Probably the InGaN mqw satellite peaks are very close to GaN peaks and it contributes to the FWHM. If you have LEDs strutures then p-GaN can increase the FWHM also depending upon the strain in you quantum wells.
Hope it answers your question.
Take care
Cordially
-Suresh
FWHM, i.e. the half width of RC curves depends on many factors. For very thin layers - and I think that MQW are - they are mainly caused by their thickness and not by a mosaic. For layers growing on the sapphire / GaN templates- bending of the whole sample is also of great importance for FWHM of the RC. I checked on an InGaN sample - 30nm thick, 18% In / GaN - 2.5 micron / sapphire (001), that the FWHM RC curve 002 and 104 (high-angle) for GaN - comes out about 0.1 degree. (High-angle incident reflexes for example -104 have a different half width than low-angle 104) For InGaN - 30nm, FWHM along the 2Theta / Omega scan is 0.3 deg. And along Om - 0.1 deg for both reflections (002 and 104). And this is consistent - If the layer does not relax - then the half width associated with the mosaic is roughly the same as for the substrate. In the work of Moram.et all, MA Moram, CF Johnston, JL Hollander, MJ Kappers, and CJ Humphreys, Citation: Journal of Applied Physics 105, 113501 (2009); doi: 10.1063 /1.3129307) you will find all the reasons for broadening the reflections in nitrides sample. By the way - asymmetrical reflections do not fully reflect the twist mosaicity . You must use the reflexes of the so-called SKEW np. 20-21.
For obtaining the symmetric broadening you can try 0004 or 0006 scans. In 0002 there can be the possibility of influence of the satellite peaks, for the superlattice structures.
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