Role of the Substrate Doping in the Activation of Fe 2+ centers in Fe implanted InP
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Role of the substrate doping in the activation of Fe2+ centers in Fe implanted InP T. Cesca1, A. Gasparotto1, G. Mattei1, A. Verna1, B. Fraboni2, G. Impellizzeri3 and F. Priolo3. INFM and University of Padova, Physics Dept., Via F. Marzolo 8, I-35131 Padova, Italy. 2 INFM and University of Bologna, Physics Dept., V.le Berti-Pichat 6/2, I-40137 Bologna, Italy. 3 INFM and University of Catania, Physics and Astronomy Dept., Via S. Sofia 64, I-95123 Catania, Italy. 1
ABSTRACT We have investigated the structural and electrical behavior of Fe centers introduced in InP by high temperature ion implantation. The lattice location of the Fe atoms and the effect of postimplantation annealing treatments have been studied by PIXE-channeling measurements. I-V, CV and DLTS analyses have been used to characterize the electrical properties related to the presence Fe2+/3+ deep traps. The results show that the background n-doping density play a crucial role in controlling the annealing behavior and the electrical activation of the Fe centers. The same effect has been observed in samples containing Fe concentrations both above and below the Fe solubility threshold in InP. INTRODUCTION Fe is a key impurity in InP-based materials and technology. Thanks to its deep acceptor character it is widely used to induce semi-insulating behavior in both bulk and epitaxial materials [1]. Moreover it has interesting optical properties related to luminescent emission in the midinfrared spectral region which can be exploited to produce mid-IR emitter devices, LED or lasers [2]. In both cases in order to display these properties, high concentrations of Fe atoms have to occupy substitutional In positions in the InP crystal. In the past the authors have demonstrated that very high densities of electrically and optically active Fe2+ centers can be incorporated in InP by high temperature ion implantation [3]; by this method damage-related undesired reactions can be strongly reduced and solubility limitations can be overcome, creating a supersaturation of substitutional Fe atoms in a relatively undamaged crystal. Electrical compensation and semiinsulating layers with resistivities close to the intrinsic InP value can be obtained from initially ndoped InP with doping densities up to 1019 cm-3 by the proper combination of Fe implantation and annealing at temperatures above 500 °C. Post-implantation thermal treatments are necessary in order to restore the long-range order of the crystal. Nonetheless it has been shown that thermal treatments at temperatures in the range between 300 and 600°C cause both the reduction of the residual damage and the escape of Fe atoms from substitutional sites towards random interstitial positions [4]. This process deserves therefore a detailed investigation because it determines the final concentration of active Fe2+ centers which in turn controls the electrical and optical properties of the implanted and annealed samples. The dynamics of the Fe escape from substitutional sites seems to be strongly influenced by the reacti
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