Formation of gallium interstitials during zinc diffusion into gallium arsenide

Abstract

Transmission electron microscopy of transverse-section specimens has been employed to study the effect of zinc diffusion on the defect structure of tellurium-doped GaAs. Two diffusion sources were employed.

Following diffusion from a Ga₅A8₅oZn₄₅ source at 720°, the diffused region was found to be defect-free, while the non-diffused region contained a high density of perfect and faulted loops typical of heat-treated Te-doped GaAs. Using aZn₂₈AS₇₂ source at 860°, however, it was found that several defect zones were produced, the extent and defect density of which were dependent on the source-weight to ampoule-volume (SW/AV) ratio. The first zone, extending in from the surface, was free from microdefects and was followed by a zone consisting of perfect dislocation loops whose size and density increased with increasing depth. In the third zone, which lies near the diffusion front, a high density of large perfect and faulted dislocation loops was found to be present. Beyond this zone the smaller loops of the annealed material were observed. This change in the defect structure when using theZn₂₈As₇₂ source at 860°, is discussed in terms of a local disequilibrium with respect to the gallium vacancy concentration at the diffusion front where the incorporation of zinc interstitials onto the gallium sub-lattice occurs at its maximum intensity. By comparison, diffusions using the Ga₅As₅₀Zn₄₅ source at 720° are much slower, thereby allowing a situation much nearer equilibrium to be established.