Synchrotron X-ray Topography Characterization of Commercial GaN Substrates for Power Electronic Applications

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As one of the most important wide bandgap semiconductors, Gallium Nitride (GaN) has many applications in power electronic devices such as inverters and switches, as well as optoelectronic devices like light emitting diodes.[1] However, high-quality bulk GaN growth is still limited by the availability of growth techniques. Two most popular growth method for GaN are hydride vapor phase epitaxy (HVPE) [2, 3] and ammonothermal [4, 5] method. HVPE method uses foreign substrates, such as sapphire, gallium arsenide or silicon carbide, which gives a large dislocation density due to significant lattice mismatch and difference in coefficients of thermal expansion. However, in ammonothermal method, native seeds were used to minimize the effects of lattice mismatch and a retrograde direction of GaN transport inside the growth system was utilized to exclude most of the contamination and undesirable phases. So, ammonothermal method gives a much better quality.In this study, GaN substrates of both HVPE (Figure 1) and ammonothermal (Figure 2) methods have been characterized by synchrotron monochromatic beam X-ray topography (SMBXT)[6]. The distribution of threading screw/mixed dislocations (TSDs/TMDs), threading edge dislocations (TEDs) and basal plane dislocations (BPDs) is characterized. Ray tracing simulations are adopted to confirm the types of dislocations. The comparison of defect distribution between HVPE and ammonothermal samples has been conducted by both SWBXT and High-resolution X-ray Diffraction (HRXRD).