Development of photonic crystal cavities to enhance point defect emission in silicon carbide
Bracher, David Olmstead
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AbstractSilicon carbide (SiC) is a semiconductor with a long history of use in a range of fields, finding applications in optoelectronics, high-power electronic devices (like field-effect transistors), and microelectromechanical systems, among others. In addition to this wide-ranging utilization, SiC is now being explored for its quantum properties. Within the field of quantum information science, there is an on-going effort to develop platforms for qubits in the solid state. One promising candidate for such qubits is semiconductor point defects. To that end, an enormous body of work has been put forth to study the nitrogen-vacancy center in diamond. Complementing this work, point defects in a number of other materials, most prominently SiC, have been explored. Indeed, SiC defects have been shown to have excellent properties that may allow them to be used for quantum sensing, quantum communication, and quantum computing. Moreover, there are many advantages to working with SiC, including near infrared defect emission, lower material cost, and large variety of available defects.
One of the most important features of these point defects is the link between their spin state and their optical emission. To better take advantage of this spin-photon connection, it is crucial to develop optical microcavities, in which the defects can be embedded. In particular, a specific portion of the defect emission spectrum, the zero phonon line (ZPL), is needed when performing many intriguing quantum protocols. Unfortunately, only a small portion of the defect emission goes into this zero phonon transition, meaning that these protocols can be extremely inefficient to carry out. Through the Purcell effect, optical cavities offer a means of modulating the defect emission to increase the ZPL emission fraction. Therefore, well-coupled cavity-defect devices would be an important tool in furthering the use of SiC for quantum applications. Cavity-defect coupling has been explored in diamond but very little has been done in SiC. Thus, this work develops a photonic cavity platform for enhancement of SiC defect emission.
In this work, we utilize the 4H-SiC polytype to design and fabricate 1D nanobeam photonic crystal cavities (PCC). We assess a variety of designs and demonstrate how to controllably tune the resonant wavelengths of these cavities. We then study how best to incorporate defects within the cavities and determine how to maximize our ability to achieve a large degree of cavity-defect coupling. As a result, we are able to, for the first time, demonstrate Purcell enhancement of defects in SiC, specifically silicon vacancies. We measure up to 90-fold enhancement of two closely linked ZPLs and use the cavity interaction to explore the properties of these ZPLs. Additionally, we design, fabricate, and measure another type of cavity, the crossbeam PCC. These cavities could find use in simultaneous enhancement of the ZPLs of multiple defect species inside the same cavity volume. Lastly, the aforementioned experiments are undertaken using p-type SiC as the caviy material. However, the defects have much more favorable properties inside unintentionally doped SiC. Therefore, we design new SiC heterostructures that incorporate such unintentionally doped SiC in our PCCs. We use this material to fabricate cavities and observe both good photonic properties and improved spin properties.
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