The diffusion of Cd into single crystals was investigated at 756 to 1201C. The penetration profiles, as measured by means of secondary ion mass spectroscopy and spreading-resistance profiling, agreed with each other and were consistent with the operation of a kick-out diffusion mechanism. The involvement of vacancies, via a dissociative mechanism, was excluded and it was possible to deduce effective Cd diffusivities and Ga diffusivities from the Cd profiles; as mediated by doubly positively charged Ga self-interstitials. The effective Cd diffusivities (figure 1) which were obtained in As-rich and As-poor ambients were consistent; as were the Ga diffusivity data. Under 1atm of As vapour pressure, and electrically intrinsic conditions, the Cd diffusivity results could be described by:

D (cm2/s) = 1.76 x 104 exp[-4.80(eV)/kT]

The diffusivity of doubly positively charged Ga self-interstitials could be described by:

D (cm2/s) = 3.5 x 104 exp[-5.74(eV)/kT]

Overall, the results strongly suggested that, in heavily p-doped GaAs, atomic transport on the Ga sub-lattice was governed by self-interstitials rather than by vacancies.

Diffusion of Cd in GaAs and its Correlation with Self-Diffusion on the Ga Sublattice G.Bösker, N.A.Stolwijk, H.Mehrer, U.Södervall, W.Jäger: Journal of Applied Physics, 1999, 86[2], 791-9

Figure 1

Diffusion of Cd in GaAs