Two-Dimensional Damage Distributions Induced by Localized Ion Implantations
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TWO-DIMENSIONAL DAMAGE DISTRIBUTIONS INDUCED BY LOCALIZED ION IMPLANTATIONS M.M. FAYE, L. LAANAB, J. BEAUVILLAIN, A. CLAVERIE CEMES-LOE/CNRS, 29 rue J. Marvig, 31055 Toulouse, France C. VIEU, G. BENASSAYAG L2M/CNRS, 196 avenue H. Ravera, 92225 Bagneux, France
ABSTRACT A general method is presented for calculating the spatial distribution of damage generated by localized implantation in semiconductors. Implantation through masks and focused ion beam Implantation in GaAs are simulated and compared to cross-sectional transmission electron microscopy observations. An excellent agreement is obtained when a depth-dependent lateral straggle is considered. Arbitrarily shaped mask edges and different compositions for the mask and the substrate are included in the calculations as well as realistic current profiles of the ion spot in the case of focused ion beam implantations. Simulations and experiments clearly demonstrate the potential application of localized implantations to fabricate lateral quantum nanostructures. INTRODUCTION The introduction of an excess of defects in semiconductor heterostructures is nowadays a widespread technique to modify the shape and composition of the layers due to an enhancement of the interdiffusion at the heterointerfaces. This layer disordering which can modify the effective energy gap and refractive index has been successfully applied to the fabrication of novel devices [1]. Among the various sources of damage generation ion implantation has gained precedence because the technique is very reproducible and the amount of defects which fixes the mixing rate can be easily controlled. The remaining question concerns the limit to the downsizing of the lateral dimensions achievable by localized implantation. Indeed, one can have some doubts about the potential application of this technique to fabricate lateral quantum nanostructures where typical defect-free regions of 5-50 nm wide must be sandwiched between highly irradiated areas. The spatial localization of the bombardment is commonly achieved by the use of a masking layer [2] or by scanning a fine focused ion beam on the surface of the sample [3]. In this paper the lateral selectivity of the damage generation is investigated for these two techniques. Following Claverie et al. [4] we use a simple mathematical approach to describe the spatial damage distribution by convoluting the damage point response function due to a single ion with a function describing the injection of the ions at the surface. Due to the simplicity of our procedure many refinements can be included in the calculation such as depth-dependent lateral straggles, arbitrarily shaped mask edges, different compositions for the masking layer and the substrate and realistic current profiles of the FIB spot. The same general formalism is used to describe implantation through masks and focused ion beam (FIB) implantations. In both cases the simulations are compared to cross-sectional transmission electron microscopy (XTEM) observations of amorphous zones generated by the accumulation
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