InAl(Ga)N: MOCVD thermodynamics and strain distribution

Abstract

One of the obstacles in obtaining high quality and high indium-molar fraction InAl(Ga)N is the higher vapor pressure of nitrogen over group-III elements, especially indium. In this work, we used a thermodynamically motivated approach to increase the nitrogen content in vapor phase through the ammonia input partial pressure and its role on the composition of indium-rich InAl(Ga)N layers is investigated. It is shown that the increase in indium molar fraction coincides with the ammonia input partial pressure and independent of the two growth regimes: surface kinetics limited and mass transport limited. In parallel, molecular dynamics based on empirical potentials is carried out in order to investigate the strain behavior resulting from such growth kinetics. It is unveiled that at the InAl(Ga)N/GaN interface, tensile strain on Al–N and Ga–N bonds is enhanced and compressive strain in In–N bonds is relaxed. In contrast, on top of a layer, Al–N and Ga–N bonds are comparatively relaxed and In–N bonds are relatively more compressed. Clearly, this work provides a comprehensive overview of the metal-organic chemical vapor deposition (MOCVD) thermodynamics of InAl(Ga)N layers.