Nitrogen Effusion and Self-Diffusion in Ga14N/Ga15N Isotope Heterostructures

Ga14N/Ga15N/Ga14N isotope heterostructures are used to study nitrogen self-diffusion by secondary-ion mass spectrometry and thermally activated decomposition. After interdiffusion of Ga14N and Ga15N layers at temperatures between 770°C and 970°C the diffusion profiles are measured. The isotope heterostructures are particularly well suited for self-diffusion studies because the diffusion takes place at the interface inside the GaN crystal, and therefore the analysis is free from perturbations such as surface electric fields, mechanical stress or chemical potential gradients. The temperature dependence of the nitrogen self-diffusion coefficient (D) in hexagonal GaN was determined to be 1600 cm-2 s-1 exp [(-4.1±0.4) eV/k B T], leading to a self-diffusion entropy S SD of about 10k B. The nitrogen flux through an isotope interface is compared with the nitrogen loss from a free GaN surface in vacuum above the decomposition temperature, to obtain information about the diffusion kinetics relevant for epitaxial growth and high temperature device applications.