CHARACTERIZATION OF VACANCY-TYPE DEFECTS IN SILICON AND THE APPLICATIONS TO PHOTONIC DEVICES

Abstract

The excess optical attenuation at wavelengths around 1.55 pm induced by ionirradiation of silicon-on-insulator rib waveguides was quantified. After 2.8MeV Si+ implantation at a dose of 6.3xlOl3cm'2, the measured optical loss was 430±15dBcm', suggesting that selective implantation of a relatively low dose of inert ions provides a method for modal attenuation in silicon photonic circuits. This is particularly useful for reducing optical noise or crosstalk between devices integrated on the same substrate. It was concluded that this attenuation was related to the introduction of lattice defects, predominantly silicon divacancies, caused by the implantation. Fourier transform infrared spectroscopy measurements confirmed the 1.8pm absorption band previously correlated to divacancies in silicon. Positron lifetime measurements of bulk silicon implanted with 1.5MeV H+ indicated that divacancies are the dominant vacancy-type defect present. These measurements required the development of a new model for the implantation profile of positrons emitted from 22Na. This model was based on the theory of p+ decay in conjunction with Gaussian derivative distributions developed by Makhov. Beam-based positron annihilation spectroscopy was used to measure the divacancy concentration in bulk silicon also implanted with 2.8MeV Si+. This resulted in excellent agreement with an empirical model, developed by Coleman, Burrows and Knights (CBK), which has been used previously to predict vacancy-type defect concentrations in bulk silicon for various implantation conditions. Based on the CBK model, a simple analytical expression that can be used to estimate excess optical absorption in ion implanted silicon was suggested. This expression predicts absorption of 282dBcm-1 for 2.8MeV Si+ implantation at a dose of 6.3x10l3cm'2, considerably less than the measured attenuation in the irradiated waveguides. Reasons for this discrepancy are discussed and it was concluded that considerable attenuation is associated with radiation loss due to the implantation-induced refractive index modification in the waveguides. This radiation loss, which is not accounted for in the predictive analytical expression based on the CBK model, was verified using BeamProp simulations. Finally, it was demonstrated how implantation damage could be utilized to fabricate an integrated optical barrier. It was shown that a lOdB barrier with a width of 1000pm could be made with an implantation dose two orders of magnitude lower than that required for a barrier made using free carrier absorption.