11:10 AM - EL04.06.03
Application of Synchrotron X-Ray Topography to Characterization of Selective Area Doping Processes for the Development of Vertical GaN Power Devices
Yafei Liu1,Hongyu Peng1,Tuerxun Ailihumaer1,Shanshan Hu1,Balaji Raghothamachar1,Michael Dudley1
Stony Brook University, The State University of New York1
Selective area p-type doping of GaN is required for the development of vertical GaN devices that will help realize the potential of WBG semiconductor GaN in power electronics [1, 2]. Approaches being investigated include implantation followed by activation annealing by different methods, selected area etching and regrowth of p-type regions , diffusion doping and neutron transmutation . Using synchrotron X-ray topography  and complementary tools like HRXRD and Raman spectroscopy, the effect of substrate choice, implantation and annealing conditions have been evaluated on the structural quality and strain in the epilayers and regrown material. The choice of bulk GaN substrates plays an important role in the eventual extended defect configurations in the active layers. Ammonothermal-grown GaN substrate wafers show the best quality among all the wafers [6, 7]. These wafers, which are free of basal plane dislocations (BPDs), have low curvature and threading mixed dislocations (TMDs) dominant among the threading dislocations (TDs). Patterned HVPE GaN reveal a starkly heterogeneous distribution of dislocations with large areas containing low threading dislocation densities in between a grid of strain centers with higher threading dislocation densities and BPDs . The strain level of HVPE GaN substrates is very high, and the dislocation density is around 105-106 cm-2, which is much higher than 104 cm-2 of ammonothermal samples and dislocation-free areas in the patterned HVPE samples. During epitaxial growth by CVD for implantation purposes, defects in substrates are shown to replicate into the epilayer and typically no new defects are observed to be introduced at the interface. On implantation, damaged layers are generated in the epilayer as revealed by satellite peaks in double axis rocking curves. The radiation fluence and energy determine the extent of damage. Depending on annealing conditions most of the damage is healed. However, the annealing temperatures greater than 1100 C can result in introduction of inhomogeneous strains and dislocation generation. While etching by TBCl is shown to be sensitive to certain types of threading dislocations, any thermal treatment is shown to introduce basal plane dislocations. Further investigations are underway to analyze the regrowth interface for the nucleation of new defects. Results will be discussed with implications for vertical device fabrication and expected impact on device performance.
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