Gernot Gruber

Interface defects in SiC power MOSFETs - An electrically detected magnetic resonance study based on spin dependent recombination

This study presents electrically detected magnetic resonance (EDMR) measurements on a silicon carbide (SiC) MOSFET having the structure of a double-diffused silicon MOSFET (DMOS). The resonance pattern of a SiC DMOS was measured by monitoring the change of the recombination current between the source/body and the drain. The amplitude of the response has a maximum when the device is biased in depletion due to the equal concentrations of electrons and holes at the interface resulting in the most efficient recombination. The measured anisotropic g-tensor has axial symmetry with g∥ = 2.0051(4) (B ‖ c-axis), and g⊥ = 2.0029(4) (B⊥ c-axis) and the pattern shows several hyperfine (HF) peaks. We tentatively identify the observed defect as a silicon vacancy located directly at the interface.

Electrically detected magnetic resonance of carbon dangling bonds at the Si-face 4H-SiC/SiO2 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/SiO2 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 (PbC) center and the silicon vacancy (VSi) demonstrates that the PbC center is a more suitable can...

Recombination centers in 4H-SiC investigated by electrically detected magnetic resonance and ab initio modeling

Electrically detected magnetic resonance (EDMR) is a powerful technique for the observation and categorization of paramagnetic defects within semiconductors. The interpretation of the recorded EDMR spectra has long proved to be challenging. Here, defect spectra are identified by comparing EDMR measurements with extensive ab initio calculations. The defect identification is based upon the defect symmetry and the form of the hyperfine (HF) structure. A full description is given of how an accurate spectrum can be generated from the theoretical data by considering some thousand individual HF contributions out of some billion possibilities. This approach is illustrated with a defect observed in nitrogen implanted silicon carbide (SiC). Nitrogen implantation is a high energy process that gives rise to a high defect concentration. The majority of these defects are removed during the dopant activation anneal, shifting the interstitial nitrogen to the desired substitutional lattice sites, where they act as shallow...

Influence of Oxide Processing on the Defects at the SiC-SiO2 Interface Measured by Electrically Detected Magnetic Resonance

Anneals in nitrogen (N) containing atmosphere have been proven as efficient means of improving the channel mobility of SiC MOSFETs. It has been demonstrated that simultaneously the density of interface traps is reduced. However, this process is not yet fully understood. In this study we show a comparison of MOSFETs annealed in different atmospheres and compare their electrically detected magnetic resonance (EDMR) spectra with electrical parameters. We find hints for the N incorporation not only passivating but also creating or transforming defects.

Electrically detected magnetic resonance study of defects created by hot carrier stress at the SiC/SiO2 interface of a SiC n-channel metal-oxide-semiconductor field-effect transistor

This Letter reports electrical measurements as well as electrically detected magnetic resonance (EDMR) studies of defects created at the SiC/SiO2 interface of a lateral 4H-SiC n-channel metal-oxide-semiconductor field-effect transistor (MOSFET) by hot carrier stress (HCS). Both charge pumping (CP) and mobility measurements indicate severe device degradation due to the electrical stress. In accordance with the electrical measurements, a large increase in the EDMR amplitude by a factor of 27 was observed after 106 s of HCS. The defect observed in the unstressed device is anisotropic with gB||c = 2.0045(4) and gB⊥c = 2.0020(4). After the stress, the g-value changes to gB||c = 2.0059(4) and gB⊥c = 2.0019(4). During HCS, most defects are created near the n-doped drain region of the device. In this region, the crystalline structure of the SiC is distorted due to incorporation of N close to the amorphous dose. The distortion could explain the slight change in the g-value with the dominating defect or defect fami...

Identifying Performance Limiting Defects in Silicon Carbide pn-Junctions: A Theoretical Study

Dopant implantation is a high energy process which causes a significant damage to the crystal lattice and is usually accompanied by a post implantation anneal to repair the structure. Defects created in these processes may also persist in fully processed devices. Previous electron paramagnetic resonance (EPR) and EDMR studies have identified a series of nitrogen related defect complexes in N implanted silicon carbide (SiC) wafers.[1–3] This study examines the formation energy, charge transition levels and barriers to interconversion of two such defects: NCVSi and the NSiVC. The NCVSi center is favoured in a variety of charge states for a wide range of Fermi level positions. We found, however, that for Fermi level positions close to the valence band of 4H-SiC the NCVSi center is a favoured conformation with barriers to rearrangement of +1.2 eV and +3.8 eV in the neutral and +2 charge states, respectively.

An Extended EDMR Setup for SiC Defect Characterization

Only a few methods exist to observe, identify, and localize defects in SiC devices. These defects are a major limit for device performance and reliability. Presented is an improved experimental setup to investigate deep level defects using electrically detected magnetic resonance (EDMR). The method applied in this study exploits the simultaneous in-situ electron spin resonance (ESR) measurement of a standard sample (DPPH) to calibrate the magnetic field. The functionality is shown by comparing the data of an ion implanted SiC diode to results from a recent study . The in-situ B-field calibration is found to increase the accuracy of EDMR measurements by a factor of 2.5.

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/SiO2 interface. 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 PbC and the dual-PbC defects. These defects match the symmetry, hyperfine interaction, and isotopic abundance observed in the experimental EDMR spectrum.