Diffusion of Ge Donors in β-Ga2O3

Diffusion of Ge donors in beta-Ga2O3 is studied using a combination of secondary-ion mass spectrometry, diffusion simulations, and first-principles calculations, and compared to previous studies on Sn diffusion. Ge is implanted into ((2) over bar01)-oriented samples and annealed at temperatures from 900 to 1050 degrees C for a total of 8 h. From previous first-principles calculations, Sn is predicted to diffuse via the formation of a mobile complex with V-Ga that migrates through a sequence of exchange and rotation jumps. Herein, it is similarly predicted that Ge diffusion is mediated by V-Ga. However, the microscopic mechanism differs, as Ge can diffuse more easily through exchange combined with complex dissociation, rather than rotational jumps. This is explained by the difference in Ga-site preference of Ge compared to Sn, and the three-split mechanism that enables low migration barriers for V-Ga. The dissociation mechanism leads to a considerably faster transport for Ge as compared to Sn. The experimentally obtained Ge diffusion profiles are successfully fitted using a reaction-diffusion model based on the predicted diffusion mechanism, yielding a migration barrier of 2.5 +/- 0.2 eV for the complex. The 2.72 eV obtained from first-principles calculations is in good agreement with this value.