Characterization and Integration of Defect-Mediated Photodetectors for Silicon Photonic Circuits

Abstract

<p>Silicon photonic interconnects represent a possible solution to the problems associated with scaling electrical interconnects to higher data rates. Defectmediated optical detectors fabricated via inert ion implantation incorporated with optical waveguides in such a circuit allow control and monitoring of the optical signal and can be fabricated entirely using standard Complementery Metal-Oxide Semiconductor (CMOS) fabrication steps, thus simplifying the task of integrating optical functionality alongside electronic circuits on a chip.</p> <p>In the work described in this thesis, the defects involved in the detection process at wavelengths at and around 1550 nm have been investigated. For low-dose ion implantation, the defect which dominates optical absorption and detection is shown to be an acceptor with an energy of 0.41 ± 0.02 eV below the conduction band, properties consistent with the silicon divacancy. A novel technique for optical characterization has been developed and used to determine the optical cross-section of this defect to be 6 x 10-17 cm2 for a wavelength of 1550 nm. Defect concentration versus thermal annealing temperature was evaluated, and waveguide integrated detectors were fabricated and used to characterize optical absorption and quantum efficiency as a function of the annealing conditions.</p> <p>A monolithically integrated device comprising a defect-enhanced photodiode and a variable optical attenuator was designed, modeled, fabricated, and demonstrated with the photodiode used to monitor and control the optical output power. To illustrate the potential of such a device, it was operated as a dynamic channel leveller with external software used to mimic an electronic feedback loop between the detector and attenuator. The channel leveller was able to maintain ± 1 dB output power variation across a 7-1 0 dB input dynamic range for wavelengths ranging from 1530 nm to 1570 nm.</p> <p>Additionally, a tunable resonant defect-enhanced photodiode was designed, modeled, fabricated, and characterized. It is shown that resonant effects can be used to obtain similar responsivity from a small, lightly absorbent photodiode as would otherwise require a longer, highly absorbent photodiode, thus enabling very low minimum detectable power. The device responsivity was measured to be greater than 0.1 A/W for wavelengths ranging from 1510 nm to 1600 nm, with individual wavelengths selectable by tuning the resonance peak. The device was also demonstrated as a variable optical attenuator with 20 dB extinction, less than 44 m W switching power, and integrated monitoring.</p> <p>The devices described in this thesis represent the first reported demonstrations of integrated optical power control, dynamic channel levelling, and tuneable resonant detection using defect mediation in a silicon photonic circuit.</p>