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SUMMARY:Bragg Diffraction Imaging Analysis of Crystal Defects in GaN Subst
 rates - Comparison of the growth method and the seed approach - Dr. Lutz K
 irste\, Fraunhofer Institute for Applied Solid State Physics (IAF)\, Freib
 urg\, Germany 
DTSTART:20240201T151500Z
DTEND:20240201T161500Z
UID:TALK211093@talks.cam.ac.uk
CONTACT:Julie Smith
DESCRIPTION:To date\, two growth methods\, hydride vapor-phase epitaxy (HV
 PE) and ammonothermal method\, have been used to produce commercially avai
 lable GaN substrates. Some manufacturers have successfully produced GaN su
 bstrates up to 4 inches in diameter\, n-type and semi-insulating. However\
 , there are significant differences in the defect density of the GaN subst
 rates. For example\, the threading dislocation density (TDD) varies in the
  range of 103 - 106 cm-2\, depending on the supplier. The crucial aspect r
 egarding the resulting defect density of the GaN substrates seems to be th
 e seed approach\, foreign seed or native seed\, rather than the crystal gr
 owth method. Only with native GaN seeds is it possible to produce GaN subs
 trates with the low defect density required to realize electronic and opto
 electronic devices with high performance\, reliability and lifetime.\n\nIn
  this work\, the defect structure of commercial GaN substrates grown by th
 e ammonothermal method with a foreign seed approach as well as with a nati
 ve seed approach and HVPE grown GaN with a foreign seed approach is invest
 igated. In addition\, non-commercial HVPE-GaN produced by a native seed ap
 proach is being studied. For our studies\, we used two different Bragg dif
 fraction imaging techniques\, namely laboratory Lang technique topography 
 (L-XRT) and synchrotron rocking curve imaging (RCI). \n\nIt is demonstrate
 d that ammonothermally grown GaN substrates (Am-GaN) based on native seed 
 approach show a strong Borrmann effect\, the anomalous transmission of X-r
 ays\, due to high structural perfection [1]. The same applies to HVPE-GaN 
 grown with native seed. In contrast\, Am-GaN and HVPE-GaN substrates produ
 ced with a foreign seed approach show a mosaic defect structure with high 
 TDD. Here\, the Borrmann effect is nearly fully blocked in this material. 
 RCI is used to quantify the lattice distortion. For the GaN substrates wit
 h native seed approach\, it is in the range of 2-3 arcsec\, while for the 
 GaN substrates with foreign seed approach\, it reaches levels of up to 20 
 arcsec. This study clearly shows that low-defect GaN substrates can only b
 e produced using low defect native seeds.\n
LOCATION:Goldsmiths 2 & https://zoom.us/j/96836714124
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