In situ monitoring and Hall measurements of GaN grown with GaN buffer layers

High-quality gallium nitride (GaN) film was obtained using a GaN buffer layer on a sapphire substrate. Using low-temperature Hall measurements, we obtained a maximum mobility about 3000 cm2/V s, at around 70 K. This mobility value is the highest reported, to our knowledge, for GaN films. The infrared radiation transmission intensity oscillations, which were caused by interference effects, were observed by means of an infrared radiation thermometer during GaN growth. The growth process of GaN film with GaN buffer layers was almost the same as that of GaN film with AlN buffer layers except when the thickness of GaN buffer layers was small. When the thickness of GaN buffer layers was small, an additional new growth process, in which the surface of GaN film became rough during the growth, was observed. The GaN growth with GaN buffer layers had a tendency to improve the surface morphology even if it became poor due to excess Si doping or low buffer layer thickness.