P-Type Impurities in 4H-SiC Calculated Using Density Functional Theory

We have investigated the p-dopant potential of 14 different impurities (Be, B, F, Mg, Al, Ca, Sc, Cu, Zn, Ga, In, Ba, Pt, and Tl) within 4H-SiC via Density Functional Theory (DFT) calculations using a hybrid density functional. We analyse the incorporation energies of impurity atoms on Si and C sites as well as the character of lattice distortion induced by impurities. The calculated thermal ionization energies confirm that Al and Ga on the Si site are the best candidates for p-doping of 4H-SiC. Although we find some correlation of incorporation energies with atomic radii of impurities, the difference in chemical interaction with neighbouring atoms and strong lattice distortions play important roles in determining the impurity incorporation energies and charge transition levels. We find Al to still be the best and most industrially viable p-dopant for 4H-SiC

Electrically detected magnetic resonance of carbon dangling bonds at the Si-face 4H-SiC/SiO2_2 interface

SiC based metal-oxide-semiconductor field-effect transistors (MOSFETs) have gained a significant importance in power electronics applications. However, electrically active defects at the SiC/SiO$_2$ interface degrade the ideal behavior of the devices. The relevant microscopic defects can be identified by electron paramagnetic resonance (EPR) or electrically detected magnetic resonance (EDMR). This helps to decide which changes to the fabrication process will likely lead to further increases of device performance and reliability. EDMR measurements have shown very similar dominant hyperfine (HF) spectra in differently processed MOSFETs although some discrepancies were observed in the measured $g$-factors. Here, the HF spectra measured of different SiC MOSFETs are compared and it is argued that the same dominant defect is present in all devices. A comparison of the data with simulated spectra of the C dangling bond (P$_\textrm{bC}$) center and the silicon vacancy (V$_\textrm{Si}$) demonstrates that the P$_\textrm{bC}$ center is a more suitable candidate to explain the observed HF spectra.Comment: Accepted for publication in the Journal of Applied Physic

Modelling the interactions of NO in a-SiO2

Nitric oxide (NO) is often used for the passivation of SiC/SiO2 metal oxide semiconductor (MOS) devices. Although it is established experimentally, using XPS, EELS, and SIMS measurements, that the 4H-SiC/SiO2 interface is extensively nitridated, the mechanisms of NO incorporation and diffusion in amorphous (a)-SiO2 films are still poorly understood. We used Density Functional Theory (DFT) to simulate the diffusion of NO through a-SiO2 and correlate local steric environment in amorphous network to interstitial NO (NOi) incorporation energy and migration barriers. Using an efficient sampling technique we identify the energy minima and transition states for neutral and negatively charged NOi molecules. Neutral NO interacts with the amorphous network only weakly with the smallest incorporation energies in bigger cages. On the other hand NOi -1 binds at the intrinsic precursor sites for electron trapping

Origin of trap assisted tunnelling in ammonia annealed SiC trench MOSFETs

The interface between silicon carbide (SiC) and silicon dioxide (SiO2) is of considerable importance for the performance and reliability of 4H-SiC (trench) metal oxide semiconductor field effect transistors (MOSFETs) and various different post oxidation anneals (POAs) have been used to optimize its quality. Whereas nitric oxide (NO) POA leads to very reliable and well performing MOSFETs, ammonia (NH3) can further improve the device performance, however, at the cost of the gate oxide (GOX) reliability, e.g. leading to trap assisted tunneling (TAT). We investigate the origin of TAT and GOX leakage in differently annealed gate oxides experimentally, using 4H-SiC trench MOSFETs, and theoretically, using Density Functional Theory (DFT) simulations. Our findings reinforce the view that the NO anneal for SiC devices results in the best overall quality as devices annealed in NH3 and nitrogen N2 show higher oxide charge density and leakage currents. DFT simulations demonstrate that, contrary to what has often been assumed so far, NH3 annealing leads to the formation of additional hydrogen related defects, which open leakage paths in the oxide otherwise not present in NO treated oxides

Hydrogen-induced rupture of strained Si─O bonds in amorphous silicon dioxide

Using ab initio modeling we demonstrate that H atoms can break strained Si─O bonds in continuous amorphous silicon dioxide (a−SiO2) networks, resulting in a new defect consisting of a threefold-coordinated Si atom with an unpaired electron facing a hydroxyl group, adding to the density of dangling bond defects, such as E′ centers. The energy barriers to form this defect from interstitial H atoms range between 0.5 and 1.3 eV. This discovery of unexpected reactivity of atomic hydrogen may have significant implications for our understanding of processes in silica glass and nanoscaled silica, e.g., in porous low-permittivity insulators, and strained variants of a−SiO2

Effects of nitridation on SiC/SiO2 structures studied by hard X-ray photoelectron spectroscopy

SiC is set to enable a new era in power electronics impacting a wide range of energy technologies, from electric vehicles to renewable energy. Its physical characteristics outperform silicon in many aspects, including band gap, breakdown field, and thermal conductivity. The main challenge for further development of SiC-based power semiconductor devices is the quality of the interface between SiC and its native dielectric SiO$_2$. High temperature nitridation processes can improve the interface quality and ultimately the device performance immensely, but the underlying chemical processes are still poorly understood. Here, we present an energy-dependent hard X-ray photoelectron spectroscopy (HAXPES) study probing non-destructively SiC and SiO$_2$ and their interface in device stacks treated in varying atmospheres. We successfully combine laboratory- and synchrotron-based HAXPES to provide unique insights into the chemistry of interface defects and their passivation through nitridation processes

Effects of nitridation on SiC/SiO(2)structures studied by hard X-ray photoelectron spectroscopy

SiC is set to enable a new era in power electronics impacting a wide range of energy technologies, from electric vehicles to renewable energy. Its physical characteristics outperform silicon in many aspects, including band gap, breakdown field, and thermal conductivity. The main challenge for further development of SiC-based power semiconductor devices is the quality of the interface between SiC and its native dielectric SiO2. High temperature nitridation processes can improve the interface quality and ultimately the device performance immensely, but the underlying chemical processes are still poorly understood. Here, we present an energy-dependent hard x-ray photoelectron spectroscopy (HAXPES) study probing non-destructively SiC and SiO2 and their interface in device stacks treated in varying atmospheres. We successfully combine laboratory- and synchrotron-based HAXPES to provide unique insights into the chemistry of interface defects and their passivation through nitridation processes

Interface chemistry and electrical characteristics of 4H-SiC/SiO2 after nitridation in varying atmospheres

SiC has immense potential as the semiconductor for future metal–oxide–semiconductor (MOS) devices. One of the greatest advantages and disadvantages of SiC is its native oxide, SiO2. The ability to use established SiO2 processes to create a reliable dielectric directly on the SiC semiconductor is very desirable. However, the SiC/SiO2 interface exhibits high defect densities leading to detrimental effects on device performance. A variety of treatment processes, often in N-containing atmospheres, has been shown to compensate defects and increase device performance. However, information on the local chemistry at the interface after such processes is scarce, which limits the understanding of the interface and consequently the targeted improvement of device characteristics. The present work uses X-ray photoelectron spectroscopy (XPS) to systematically study the elemental distributions and chemical environments across the 4H-SiC/SiO2 interface after high temperature nitridation treatments in a variety of atmospheres. In particular the use of a NO/NH3 combinatorial process is of great interest as it influences the defect chemistry on both the oxide and carbide side of the interface. We are able to identify N–C–Si environments as the dominant defect states at the interface. The XPS results are correlated with electrical and reflective index measurements, providing new, detailed insights into the relationship between interface chemistry and device behaviour

Recombination defects at the 4H-SiC/SiO2 interface investigated with electrically detected magnetic resonance and ab initio calculations

The selectivity of electrically detected magnetic resonance (EDMR) is utilized to probe the dominant recombination defect at the Si-face 4H-SiC/SiO2interface. The nature of this defect has long been debated with the two main candidates being the Si vacancy (VSi) or the C-dangling bond (PbC). Through comparison between experimental EDMR measurements and ab initio calculations, an important performance limiting recombination defect observed with EDMR in the current generation of nMOSFETs is reasonably explained as a combination of the PbCand the dual-PbCdefects. These defects match the symmetry, hyperfine interaction, and isotopic abundance observed in the experimental EDMR spectrum