Physica B 308–310 (2001) 854–857 Mechanism of zinc diffusion in gallium antimonide S.P. Nicols a,b, *, H. Bracht c , M. Benamara b , Z. Liliental-Weber b , E.E. Haller a,b a University of California at Berkeley, 1 Cyclotron Road MS 2-200, Berkeley, CA 94720, USA b Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA c Institut f . ur Materialphysik, University of M . unster, M . unster, Germany Abstract Zn diffusion experiments in GaSb at temperatures between 5001C and 6501C were performed using GaaZn alloy sources. For surface Zn concentrations exceeding 10 20 cm 3 , extended defects were detected using cross-sectional transmission electron microscopy (TEM). These defect networks correlate directly with the observed kink and tail profile shape. For lower Zn doping levels the kink disappears. The profiles of these samples reflect the diffusion behavior of Zn in virtually defect-free GaSb and are accurately described by a Ga interstitial controlled mode of Zn diffusion via the kick-out mechanism. Neutral and singly positively charged Ga interstitials mediate Zn diffusion at Zn doping levels of 12  10 19 and 310  10 19 cm 3 , respectively. The contribution of neutral Ga interstitials to Ga diffusion deduced from fitting experimental Zn profiles is in agreement with the directly measured Ga self-diffusion coefficient in GaSb isotope heterostructures. This provides strong evidence that Ga diffusion in undoped GaSb under Ga-rich conditions is mainly mediated by neutral Ga interstitials. Published by Elsevier Science B.V. Keywords: Zinc diffusion; Gallium antimonide; Kick-out model; Ga self-interstitial 1. Introduction The understanding of both self- and foreign-atom diffusion in semiconductor systems is of fundamental importance. Diffusion in semiconductors is mediated by native point defects in the crystalline lattice. Diffusion is one of only a few methods that can provide information on point defect properties such as equilibrium concen- trations, formation and migration energies, as well as charge states. From the technological point of view, diffusion processes govern the dopant profiles that form the junctions in all microelectronic devices. As devices are engineered with ever shrinking dimensions and higher dopant concentrations, the quantitative under- standing and control of diffusion becomes more and more important. Research in the GaSb system has recently intensified due to applications in high speed electronics as well as infrared lasers, detectors, and photovoltaics. Particular success has been seen in GaSb based heterojunction bi-polar transistors (HBTs), where switching speeds exceeding 250 GHz have been reported [1]. We have recently shown that Sb diffuses about 1000 times more slowly than Ga in intrinsic GaSb, all the way up to the melting point [2,3]. This atypically low value for Sb self-diffusion makes GaSb a very interesting material from the diffusion and point defect standpoint. In order to learn more about the influence of the Fermi level position on diffusion in GaSb, we have performed Zn doping experiments. Kyuregyan and Stuchebnikov [4] first showed that Zn diffusion from a constant surface concentration source cannot be de- scribed by the complementary error function. Instead, the diffusion coefficient is a function of the local zinc concentration. Since this publication, many groups have published results further exploring these initial findings, but no clear identification of the diffusion mechanism of Zn in GaSb has been made [5–10]. Conibeer et al. propose that Zn diffuses via a substitu- tional-intersititial mechanism [8], yet they lack sufficient evidence to support either the vacancy (Frank and Turnbull [11]) or kick-out (G . osele and Morehead [12]) mechanism. *Corresponding author. Fax: +1-510-486-5530. E-mail address: spnicols@lbl.gov (S.P. Nicols). 0921-4526/01/$ - see front matter Published by Elsevier Science B.V. PII:S0921-4526(01)00913-9