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Home > News > X-ray analysis of the texture of heteroepitaxial gallium nitride films
X-ray analysis of the texture of heteroepitaxial gallium nitride films
The preparation of gallium nitride films by deposition from the vapour phase (MOCVD, MBE) may suffer from an occurrence of multiple orientations and a mixture of the wurtzite (2H) and the sphalerite (3C) polytype if nucleation and deposition conditions are not optimized. We use X-ray texture diffractometry with dedicated beam optics and various scanning techniques to check for the presence of unwanted orientations and phases in a quick and semi-quantitative manner. A variety of GaN films showing multiple orientations were analyzed with respect to the nature of polycrystalline growth. These films were deposited by MOCVD on sapphire substrates. From X-ray polefigures and approximations of the texture by model components we found that the 2H and 3C orientations in these films are interrelated via stacking faults on {0001} and {111} planes, respectively. To obtain a single crystalline film orientation, a suppression of the formation of stacking faults is required. This has been achieved under optimized MOCVD conditions. As is evidennt by X-ray diffractometry, these films are single crystalline, phase pure 2H GaN films with small mosaicity spreads.
 
Fig. 1. Focussing X-ray texture diffractometer dedicated to the analysis of polycrystalline films on single crystal substrates.
 
Fig. 2. The three scanning modes used for polytype identification, for polefigure scans and for mosaicity spread measurements.
 
Fig. 3. Theoretical X-ray powder pattern of the wurtzite (2H) and the sphalerite (3C) polytypes of gallium nitride (for CuKα1).
 
Fig. 4. X-ray polefigures in stereographic projection of two different samples taken at the 200 reflection position shown in Fig. 3. The left picture gives unambiguous evidence of the presence of the 3C polytype. From peak positions two primary orientations and the presence of {111} twins to these orientations are deduced.
 
Source: Materials Science and Engineering: B
 
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