GaN grown by molecular beam epitaxy at high growth rates using ammonia as the nitrogen source

Abstract

The 9.5 eV bond energy of the nitrogen molecule makes it very difficult to break it up into atoms and incorporate in III–V nitride compounds grown by molecular beam epitaxy (MBE). By comparison, it is relatively easy to dissociate ammonia due to the existence of a catalytic effect on the GaN surface when there is Ga present. Using ammonia as the nitrogen source, we have achieved high quality GaN by MBE at a growth rate as high as 1 μm/h. This is an order‐of‐magnitude faster than previously reported using electron‐cyclotron resonance plasma‐assisted growth. Most importantly, our results indicate that there is no intrinsic limit to the growth rate of GaN using ammonia, a situation similar to that of conventional III–V MBE using gas sources. The unintentional n‐type doping as low as 2×10¹⁷ cm⁻³ at room temperature. In addition, room‐temperature hole densities of 4×10¹⁷ cm⁻³ in Mg‐doped GaN films have been achieved without postgrowth annealing. Low‐temperature photoluminescence for both undoped and Mg‐doped GaN are dominated by near band‐edge emissions without deep‐level related luminescence, indicative of high quality materials.