Enhancing GaN Self Separation in HVPE by Use of Molybdenum

We prepared 2”-GaN wafers as templates for a self separation process which is happening during cooldown after growing thick layers of GaN in our hydride vapor phase epitaxy (HVPE) reactor. Our templates process starts with GaN grown by metalorganic vapor phase epitaxy (MOVPE) directly on sapphire. These GaN layers are getting masked with 200nm of SiN that is structured by means of optical lithography. These masks are subsequently overgrown with a thin GaN layer by MOVPE. When overgrowing these templates with thick layers of GaN in HVPE, several problems occur. Because of GaN nucleation on the wafer side, the top layer is clamped to the sapphire substrate. This hinders separation during cooldown. Moreover mis-shaped material is growing at the wafer edge in very long growth runs. Both problems can be addressed by using molybdenum to locally influence the V-III ratio during growth.