Silicon photonics is well suited to overcome the interconnect bottleneck currently limiting performance in electronic integrated circuits. Photonic interconnects benefit from higher bandwidth, reduced power consumption, and improved scaling with device size relative to their electronic counterparts. Realization of photonic interconnects on a Si platform would enable monolithic integration of electronic and photonic elements, thereby leveraging the considerable infrastructure developed by the Si electronics industry. Inspired by this goal, researchers in the field of Si microphotonics have demonstrated most of the capabilities required for optical communication, including waveguides, modulators, filters, switches and detectors. The key element missing from the Si photonics toolkit remains a monolithic light source.
In this work, we study two of the most promising materials in the search for a Si based light source: silicon nanocrystals (Si-nc) and erbium doped glass (Er:SiO2). We developed fabrication processes for both of these materials and performed extensive material characterization to acquire the parameters governing their respective rate equation models. We then used our model to design a series of light emitting devices. We first designed Si-nc distributed Bragg reflector (DBR) microcavities for enhanced spontaneous emission and lasing. The optimized vertically emitting structure exhibited a quality factor of 115 and a peak luminescence enhancement factor of 14.5. We then fabricated a device based on our modeling and observed an experimental quality factor of 140 and an enhancement factor of 15.2.
We also applied our simulation tool to investigate amplification and enhanced spontaneous emission in Er:SiO2 based devices. Due to the low refractive index of Er:SiO2, we presented a horizontal slot geometry in which the Er:SiO2 layer is sandwiched between Si layers. We used a modesolver to optimize this geometry and then integrated it in a ring microcavity to study enhanced spontaneous emission. Simulations of the optimized device predicted a 35 fold enhancement in the peak luminescence.
We then sought to address the requirements of a Si compatible light source for optical interconnects by designing an electrically pumped, complementary metal-oxide-semiconductor (CMOS) compatible laser with telecom wavelength emission. Leveraging the efficient electroluminescence (EL) in Si-nc films and the telecom wavelength lasing capabilities of Er:SiO2, we proposed integrating the two materials in a concentric microdisk structure. In the proposed structure, EL from an inner Si-nc disk acts as an optical pump for an Er:SiO2 laser in the outer disk. We used our modeling tool to confirm the proposed device behavior and optimize the geometry. We then fabricated a series of preliminary light emitting structures including Si-nc microdisks, Si-nc microgears, and concentric Si-nc/SiO2 and Si-nc/Er:SiO 2 microdisks. We developed two experimental characterization setups for studying whispering gallery modes (WGMs) in these raised resonators, one based on collecting emission in the far-field and the other based on coupling emission to a tapered fiber. We performed the first comparison of these characterization techniques, discussed their relative merits, and identified the regimes of operation in which each is appropriate.
Using these characterization techniques, we tested our Si-nc microdisks, microgears and concentric microdisks. We then performed the first investigation of microgear resonators using a Si based light emitting material. We then developed a fabrication process for Si-nc/Er:SiO2 concentric microdisks in accordance with our two-stage laser design. Characterization of these concentric microdisks confirmed the existence of Si-nc based pump modes and Er:SiO 2 based signal modes. We also developed a semi-analytic model to predict lasing thresholds in this device in terms of Si-nc pump power. We subsequently derived an experimental technique to measure the Si-nc pump power in our fabricated device as an input parameter for our model. Based on this analysis, we identified the optimization required to achieve lasing in the proposed concentric microdisk structure. (Abstract shortened by UMI.)