Diffusion and activation of Zn implanted into InP:S

Abstract

The aim of this work is to compare carrier concentration, diffusion coefficient and shape of the zinc atomic profile in InP layers treated under different annealing conditions. Zn implanted InP:S (4×10 18 at/cm 3—active dopant) bulk samples were investigated. Samples were implanted to a fluence of 1×10 16 cm −2 at an energy of 150 keV and then coated with a 100 nm thick AlN polycrystalline film, using sputter deposition followed by annealing at temperatures in the range 500–900 °C for various different conditions. After removal of the AlN films the extent of diffusion of the implanted species was characterized using the SIMS (Secondary Ion Mass Spectrometry) technique whilst carrier concentration was evaluated by C– V profiling. The depth profiles of in-diffused zinc strongly indicated that the diffusion coefficient D was concentration-dependent. The diffusivity of Zn was found largest when InP was annealed with phosphorus overpressure combined with the AlN cap; in case of annealing at 700 °C a Zn concentration of 2×10 19 cm −3 was achieved. The diffusion range under phosphorus overpressure was almost twice that in vacuum and this is interpreted in terms of the generation of additional vacancies in the In sub-lattice. C– V measurements showed clearly that application of protective AlN together with phosphorus overpressure causes sulphur donors compensation and results in acceptor concentration of 1×10 18 cm −3 and consequently, in the formation of a well-defined p–n junction. The activation efficiency of Zn atoms can be estimated to be about 30%, without additional heat treatment. The Boltzmann–Matano analysis was employed to evaluate the concentration-dependent diffusion coefficient of Zn in InP.