Co-Implantation and the Role of Implant Damage in the Thermal Stability of Implanted Helium in Indium Phosphide
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Co-Implantation and the Role of Implant Damage in the Thermal Stability of Implanted Helium in Indium Phosphide Todd W. Simpson and Ian V. Mitchell Department of Physics & Astronomy, University of Western Ontario, London, Ontario, N6A3K7, Canada ABSTRACT The thermal stability of 3He implanted into single crystal indium phosphide has been studied. Helium diffuses in the 200°C-300°C temperature range unless stabilized by bubbles which trap helium up to the 400°C-500°C temperature range. The efficiency of bubble formation, as measured by the fraction of implanted helium retained to 400°C is increased by: 1) increasing the helium fluence, 2) increasing the temperature ramp rate, 3) co-implantation with a second ion species, or 4) implanting at elevated temperature. The mechanism by which these processes enhance bubble formation can be understood in terms of a model where the nucleation of bubbles occurs at elevated temperature in the presence of both lattice defects and helium atoms. INTRODUCTION Ion implantation induced exfoliation has generated significant interest in the ion beam community, following the description of the smart-cut process in 1995 for producing silicon on insulator (SOI) wafers [1]. Recently, it has been demonstrated that helium ion implantation of indium phosphide can be applied to exfoliate selected areas to controllable depths down to a few microns [2]. However, helium may also be a favourable choice for ion implantation induced intermixing of InP-based quantum well structures in integrated optoelectronics applications [3] and therefore it is crucial to determine conditions where exfoliation is avoided. To determine reliably the conditions leading to either outcome, an understanding of the behavior of implanted He in InP is required. Here, we show that implantation-induced defects provide diffusion limiting traps, presumably of vacancy type, stabilizing helium to higher temperatures. Conditions that permit rapid nucleation and growth of bubbles result in efficient trapping of helium. Helium that is retained in the implanted region to temperatures of approximately 250°C contributes to the formation of gas-containing bubbles. Once trapped in bubbles, helium is stable to temperatures of approximately 500°C. EXPERIMENT Single crystal samples of Fe-doped (100) InP were mounted for implantation on a temperature controlled nickel block using conductive silver paint on the backside. The kinetics of helium ion induced lattice damage was studied as a function of implant temperature and of post-implantation annealing temperature. For the damage studies, 4He ions were implanted at 235 keV energy (Rp=1.0µm) to a fluence of 5e15 cm-2. RBS channelling methods were used to monitor damage, at an analysing energy of 3.0 MeV. For retention studies, isotopically pure 3He was implanted at energy 1.0 MeV, for a O6.4.1
projected range (Rp) of 2.9 µm [4]. The helium ions were implanted with the substrate temperatures maintained at prescribed values, within ±2°C. Following implantation, samples were annealed either in
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