Fachbereich 11 - Physik
Institut für Materialphysik
Diffusion and Defects in Elementary and Compound Semiconductors

Mechanisms of dopant diffusion in
gallium arsenide and gallium antimonide

The approach of studying the simultaneous diffusion of self- and dopant atoms as well as self- and dopant diffusion separately, which has been shown to be very effective for the identification of native point defects in elemental semiconductors, is also applicable to group III-V compounds like GaAs. However, diffusion in such binary (AB) compounds is more complex due to the larger variety of native point defects that may be involved in the diffusion processes. Beside vacancies and self-interstitials on either sublattice, anti-site defects have to be considered. Additionally, all these defects may exist in various charge states.We have investigated the simultaneous diffusion of zinc and gallium in ⁶⁹GaAs/⁷¹GaAs isotope multilayer structures at temperatures between 618°C and 714°C. Diffusion profiles of zinc, gallium-69, and gallium-71 were measured with secondary ion mass spectrometry. Accurate modelling of the simultaneous diffusion of zinc and gallium is achieved on the basis of a gallium vacancy and gallium interstitial controlled mode of zinc diffusion. Our results put the earlier interpretation of zinc and cadmium diffusion in GaAs into question. Additional experiments on zinc diffusion in GaAs are in progress to find evidence for an alternative diffusion model.

Zinc diffusion experiments in GaSb at temperatures between 500°C and 650°C were performed using Ga-Zn alloy sources. For surface zinc concentrations exceeding 10²⁰ cm^-3, extended defects were detected with transmission electron microscopy. The defect network correlates directly with the observed kink and tail profile shape. For lower zinc doping levels the kink disappears and the profiles reflect the diffusion behaviour of zinc in virtually defect-free GaSb. These profiles are accurately described by a gallium interstitial controlled mode of zinc diffusion via the kick-out mechanism. The contribution of neutral gallium interstitials to gallium diffusion deduced from fitting experimental zinc profiles is in agreement with the directly measured gallium self-diffusion coefficient in GaSb isotope heterostructures. This provides strong evidence that gallium diffusion in undoped GaSb under gallium-rich conditions is mainly mediated by neutral gallium interstitials.

Drittmittelgeber:

Alexander von Humboldt-Stiftung, US National Science Foundation

Beteiligte Wissenschaftler:

M. Benamara (Lawrence Berkeley National Laboratory), HDoz. Dr. H. Bracht (project leader), Prof. Dr. F. Briones (University of Madrid), Dr. K. Eberl (Max-Planck Institut für Festkörperforschung, Stuttgart), Prof. Dr. E.E. Haller (Lawrence Berkeley National Laboratory and University of California at Berkeley), Dr. Z. Liliental-Weber (Lawrence Berkeley National Laboratory), S.P. Nicols (Lawrence Berkeley National Laboratory and University of California at Berkeley), M.S. Norseng (Lawrence Berkeley National Laboratory and University of California at Berkeley), Dr. J.P. Silveira (University of Madrid)

Veröffentlichungen:

H. Bracht, S.P. Nicols, E.E. Haller, J.P. Silveira, and F. Briones: Self-diffusion in ⁶⁹Ga¹²¹Sb/⁷¹Ga¹²³Sb isotope heterostructures, Journal of Applied Physics 89 (2001) 5393-5399.

H. Bracht, M.S. Norseng, E.E. Haller, and K. Eberl: Zn-diffusion enhanced Ga diffusion in GaAs isotope heterostructures, Physica B 308-310 (2001) 831-834.

S.P. Nicols, H. Bracht, M. Benamara, Z. Liliental-Weber and E.E. Haller: Mechanism of zinc diffusion in gallium-antimonide, Physica B 308-310 (2001) 854-857.

S.P. Nicols: Self- and zinc diffusion in gallium antimonide, Master Thesis, University of California at Berkeley (2002).