Summary

The major objective of this dissertation is the exploration of single electron spins in silicon carbide (SiC) and the investigation of their properties for quantum applications. It will be demonstrated that single spins in SiC can be initialized, manipulated, and read out at room temperature. Furthermore, a scalable photonic platform with embedded single electron spins is developed. The work is extended on charge state manipulation of single defects using a SiC-based opto-electronic device. Additionally, two hitherto unknown defect types are characterized in a second opto-electronic device. The results presented in this thesis are published in five publications (see Own Publications & Presentations). In the following a more detailed overview of the chapters presented in this dissertation is given.

Chapter 1 (Basics) introduces basic knowledge for the understanding of following chapters. As this thesis is focused on silicon vacancy center SiC, the host material SiC is discussed. Because SiC can occur in various crystal structures, the nomenclature and growth techniques are introduced. Next, an overview of the various defects, occurring in SiC is given, with the main focus set on the silicon vacancy center. Because only single centers are investigated, an introduction to single photon sources is given. The silicon vacancy also has a non-zero net electron spin giving rise to spin state selective optical readout and manipulation. Therefore another sub-chapter is dedicated to the relevant spin-physics. The chapter concludes with the experimental apparatus and the essential details of its operation.

In Chapter 2, the optical detection of single silicon vacancy centers in an ultra-pure SiC crystal is presented under ambient conditions. Engineering of single silicon vacancies is achieved by iteratively reducing the irradiation dose until single quantum emitters are detectable. Thereby single silicon vacancy centers in SiC exhibit photon antibunching in the measured second order correlation; a clear indication for non-classical light emission. The observed silicon-vacancy centers are both well spatially localized, and stable against photobleaching. In order to enhance the collection efficiency of single emitters a solid immersion lens is fabricated into the host crystal. To this end, focused-ion beam techniques followed by post chemical and plasma etching are employed. The collection efficiency is enhanced by a factor of about three. The chapter concludes with a demonstration of odmr measurement of a single silicon vacancy on the cubic lattice site. It exhibits a $S=3/2$ system with a zero-field splitting of 70 MHz.

Chapter 3 is dedicated to the coherent properties of a single silicon vacancy. It is shown that the ground spin states of single silicon vacancy centers can be optically initialized and read out. In addition, spin-Rabi oscillations of single silicon vacancy are presented for the first time. Next, the spin coherence time at room-temperature is determined by spin-echo measurements, reaching 200 µs. It is further shown, that in the presence of an applied static magnetic field, the Larmor precession of the nuclear fields causes the silicon-vacancy spin-echo signal to collapse and revive. The spin system in combination with hetero-nuclear spin flip-flop processes is responsible for a strong spin-echo-envelope modulation, which causes de-coherence. As shown in the last part of the chapter, nuclear flip-flop processes can be suppressed by using high magnetic fields, leading to a diluted nuclear spin bath. The result suggests that the spin coherence can exceed 2 ms at room temperature and therefore shows comparable performance to other optical defects like the nitrogen vacancy center in diamond.

In Chapter 4 a scalable photonic platform on SiC is developed. The presented platform consists of arrays of nanopillars etched into the crystal. These pillars act as waveguides for the embedded color centers. Therefore the fundamental theoretical basics for such waveguides and their simulation are introduced. Then the pillar geometry is optimized by finite-difference time-domain simulation methods, followed by a presentation of the fabrication process. It is further demonstrated, that the photoluminescence is enhanced by a factor of 2 by using a low-NA dry objective.

Chapter 5 presents charge state control of single silicon vacancies. This is achieved by taking advantage of silicon carbide as a very well developed semiconducting material. A p-i-n diode is fabricated using a chemical-vapor-deposition growth technique, which realizes doping control during growth. The fabricated electronic device enables Fermi-level adjustments by applying a bias voltage to the device. The charge state switching is then observed at the interface of the n-type and intrinsic layer by means of confocal scans. Numerical simulations are performed to obtain a deeper understanding of the band diagram of the device and the charge state switching. The results suggest that the charge and recharge behavior of the silicon vacancy site can be strongly influenced by a nearby located carbon vacancy.

In Chapter 7 the finding of hitherto unknown types of bright and stable single photon sources in an electron irradiated silicon carbide diode is presented. Their integration into opto-electronic devices is highly desired since it allows for scalable quantum application devices. For this purpose a laterally aligned p-i-n diode was designed and fabricated. In this structure hitherto unknown quantum emitters were found. It will be demonstrated, that one type of those emitters can be electrically driven, whereas the other type requires optical pumping. Importantly, these emitters feature bright and very well linear-polarized photon emission in the near infrared. These properties are key features for bright single photon sources for quantum communication and quantum interface in a scalable platform. Furthermore, the results suggests that silicon carbide host various potential quantum emitters for scalable opto-electronic quantum devices.