A study was made of the diffusion coefficient of Si in GaN under various annealing conditions. The Si was implanted into 3µm-thick GaN layers deposited onto sapphire substrates using the metal-organic vapour phase epitaxy method. Implantation was performed at room temperature to a dose of 6 x 1015/cm2 at an energy of 100keV. The samples were annealed under 1atm of N at 900-1200C; with or without an AlN protective layer. The extent of diffusion of the implanted species was characterized by using secondary ion mass spectrometry. The resultant concentration profiles were characterized by 2 diffusion fronts: slow-diffused Si atoms at high concentrations and fast-diffused Si atoms at low concentrations. The first mechanism was attributed to diffusion in the crystal bulk (substitutional migration), while the second was attributed to diffusion via grain-boundaries/dislocations. The Si diffusion coefficient in a crystal was found to be dependent upon the annealing conditions, in contrast to diffusion via the grain boundary. The calculated diffusion results for annealing, with and without an AlN layer, were given (figure 7) by:

D (cm2/s) = 6.5 x 10-11 exp[-0.89(eV)/kT]

and

D (cm2/s) = 9.1 x 10-8 exp[-1.55(eV)/kT]

respectively.

Si Diffusion in Epitaxial GaN. R.Jakiela, A.Barcz, E.Dumiszewska, A.Jagoda: Physica Status Solidi C, 2006, 3[6], 1416-9

Figure 7

Diffusivity of Sn in Epitaxial GaN

(open circles: microscopic - no AlN, open squares: macroscopic - no AlN, filled circles: microscopic - AlN, filled squares: macroscopic - AlN)