Impact of crystal-quality improvement of epitaxial wafers on RF and power switching devices by utilizing VAS-method grown GaN substrates with low-density and uniformly distributed dislocations

Impact of using low dislocation density GaN substrate grown by VAS (Void Associated separation) method on GaN-HEMT epi-wafer was investigated with regards to the point defects in the crystal. We found several hole and electron traps in the GaN crystals and each of concentration were sensitive to growth condition of epitaxial layers. There was no significant difference in the basic electrical properties such as buffer leakage current, sheet carrier density and mobility of GaN-HEMT epitaxial layers grown on SiC substrates compared to those on grown on GaN substrate with low-density and uniformly distributed dislocations using VAS method. However, photo luminescence (PL) of GaN epi-layer grown on GaN substrates showed a very high near band edge emission (NBE) and low "yellow band (YL)", which is known to come from some unknown defects in the bulk and affects a non-linear behavior of the transistors. This indicates that lower density of point defects on GaN substrates can improve the device performance. Very high breakdown of over 3000V is obtained from the p-n junction diode also grown on VAS GaN substrate.