Hydrogen and nitrogen ambient effects on epitaxial growth of GaN by hydride vapour phase epitaxy

This study presents the influence of the composition of the carrier gas on the growth of GaN by HVPE. Since no hydrogen is introduced in the vapour ph ase, the deposition is expected to be controlled by Cl desorption in the fo rm of GaCl3, as has been proposed for GaAs. However, our published model pr edicts much lower growth rates than those observed. We can account for both the observed parasitic deposition and GaN growth rate if we assume that Ga Cl3 is not at its equilibrium pressure in the deposition zone and where nuc leation takes place on the walls as well as on the substrate. This yields a high rate of parasitic nucleation even though the nominal supersaturation is vanishing small. Very little growth takes place on the substrate where t he equilibrium pressure of GaCl3 is reached. We describe similar experiment s performed with a H-2/N-2 mixture as the carrier gas. In this case, we exp ect GaN deposition to be controlled by desorption of Cl as HCl, which is kn own as the H-2 mechanism. It is speculated that the results show the existe nce of a new growth mechanism. (C) 2001 Elsevier Science B.V. All rights re served.