Silicon Carbide (SiC) is a wide bandgap semiconductor with exceptional properties that position it as a leading material for next-generation power electronics and quantum technologies. Its high breakdown field strength enables it to withstand much higher voltages than conventional silicon, leading to more compact and efficient devices. Its high thermal conductivity allows for efficient heat dissipation, crucial for high-power applications. Furthermore, SiC exhibits excellent electron mobility, facilitating faster switching speeds and reduced energy losses.

SiC exists in over 250 polytypes, each with unique characteristics. Among these, the 4H-SiC polytype has emerged as the most promising for advanced applications. Its superior properties have already led to its adoption in various applications, including electric vehicles, renewable energy systems, and industrial motor drives. SiC hosts both intrinsic and extrinsic quantum emitters, or single-photon sources, with the possibility of operating at room temperature and being both optically and electronically addressable. Moreover, the ability to grow isotopically purified 4H-SiC crystals has opened exciting avenues for quantum technologies. Precise control of the isotopic composition enables manipulation of nuclear spin and optical properties, supporting applications like quantum computing, secure communication networks, and highly sensitive sensors.

Despite the significant advancements in SiC technology in recent decades, its full potential is yet to be realized, particularly in the realm of ultra-high-power devices. This requires overcoming several challenges in the epitaxial growth process. The principal bottleneck lies in growing ultra-thick epitaxial layers, which are crucial for high-voltage applications. Achieving uniform quality and low defect density in thick epitaxial layers is a demanding task. Another challenge is achieving low doping concentrations with precise control to fine-tune the electrical properties of SiC devices. The replication of basal plane dislocation (BPD) from the substrate is well controlled; however, complete elimination and prevention of new BPDs formation is critical to ensure reliable device operation. Minimizing interfacial stress is also essential, as stress at the interface between the thick epitaxial layer and the substrate can lead to defect formation and device performance degradation. Furthermore, ensuring relatively longer minority carrier lifetimes is critical to minimize forward losses in bipolar power devices. This also includes a reduction in residual impurities, as they can significantly impact carrier lifetime, and hence device performance and reliability. For quantum applications, further suppression of impurities in epitaxial layers is crucial to improve coherence time. Additionally, wafer-scale production of photonic quantum chips requires the transfer of epitaxial layers onto insulators; however, a wafer-scale approach to prepare SiC on insulators is still missing.

This thesis addresses these challenges by advancing the understanding of the Chemical Vapor Deposition (CVD) epitaxial growth process of 4H-SiC. The focus has been to understand the influence of key growth parameters and different growth chemistries to achieve superior quality material and unlock the full potential of SiC for advanced device applications in both power electronics and quantum applications. One crucial aspect explored in this thesis is the influence of boron (B) on minority carrier lifetime in as-grown epitaxial layers of 4H-SiC (Paper 1). The minority carrier lifetime is a critical parameter in bipolar devices, as it determines how long excess charge carriers (electrons or holes) can persist before recombination. This research reveals that, beyond the well-known Z1/2 center, the shallow acceptor level of B and its associated deep D-center level also limit carrier lifetime. Through employing a novel approach of comparing transient spectroscopy results and temperature-dependent time-resolved photoluminescence decays at different wavelengths, we found that B-related defects significantly affect lifetime through carrier trapping/de-trapping and recombination. By optimizing the growth process, an exceptional 2.5 μs minority carrier lifetime is achieved in a mere 25 μm thick low-doped n-type epitaxial layer.

This thesis further examines the impact of different hydrocarbons on the surface morphology and underlying mechanisms of the 4H-SiC epitaxy. This comparative analysis serves to further confirm the fundamental differences between the two primary carbon sources, methane and propane, and their distinct effects on the characteristics of the epitaxial layers. By meticulously analyzing the effect of various carbon sources, the research identifies characteristic surface defects associated with each hydrocarbon and explores their impact on surface quality (Paper 2), impurity incorporation, and minority carrier lifetime (Paper 3). Additionally, the formation of different deep levels linked to the precursors is also examined. The findings demonstrate that employing methane as the carbon source, in contrast to the commonly used propane, yields remarkably smooth surfaces, albeit with short step bunching (SSB) as its characteristic morphological defect. Propane, on the other hand, leads to the formation of inclined line-like defects (ILLs), step bunching, and comparatively rougher surfaces. Furthermore, methane enables the achievement of extremely low intentional n-type doping. Moreover, the use of methane leads to a longer minority carrier lifetime across different C/Si ratios. In comparison, utilizing propane as the carbon source leads to higher incorporation of D-centers and the formation of additional Cl-related deep levels. Interestingly, the latter observation may be of relevance for quantum ap-plications, as Cl-related defects can serve as potential single-photon emitters in 4H-SiC epitaxial layers.

In Paper 4, the findings are applied to develop a growth process for thick epitaxial layers. This process requires careful consideration of various aspects related to both the growth dynamics and the layer quality. The principal objective is to optimize the growth rate while simultaneously maintaining excellent crystal quality and maximizing minority carrier lifetime. To achieve this, the evolution of these properties throughout the growth process is meticulously studied to identify limitations and potential avenues for further optimization. Additionally, it is observed that the surface roughness and some surface defects can be controlled by adding HCl during the epitaxial growth process; however, at the expense of reduced minority carrier lifetime. Overall, methane demonstrated significant promise for enabling the growth of extremely thick 4H-SiC epitaxial layers with improved properties.

Building on prior insights, this research further delves into the challenge of achieving high-quality epitaxial growth for ultra-thick (280 μm), 4H-SiC layers, essential for ultra-high power devices exceeding 30 kV (Paper 5). By adjusting the growth parameters such as growth rate, temperature, and carbon source, a suitable growth process was designed. This process enables the growth of an extremely thick epitaxial layer structure with a voltage handling capability of over 35 kV. The layer exhibits minimized stress and a zero BPD replication into the epitaxial layer.

In recent years, a novel approach, called remote epitaxy, has emerged to obtain free-standing semiconductor layers with varying thicknesses over 2D materials. Remote epitaxy can potentially advance the field of photonic chips on wafer-scale SiC on insulators via an easier layer transfer process. Furthermore, remote epitaxy offers significant advantages, including the potential for substantial cost reduction in SiC wafer production through substrate reusability. Paper 6 investigates the feasibility of adapting the remote epitaxial growth process for the pseudo-homoepitaxial growth of 4H-SiC. Recognizing the fundamental differences between III-V/graphene and SiC/graphene material systems, this research explores the unique challenges associated with the remote epitaxial growth of SiC. Key challenges addressed include the epitaxial growth of graphene on off-axis SiC substrates, which are preferred for straightforward polytype replication. Furthermore, the preservation of graphene is investigated in the extreme environment of SiC epitaxial growth. Finally, the possibility of growing high-quality SiC on top of a graphene layer is also explored.