No abstract

One of the main challenges in realizing 4H–SiC (silicon carbide)-based bipolar devices is the improvement of minority carrier lifetime in as-grown epitaxial layers. Although Z1/2 has been identified as the dominant carrier lifetime limiting defect, we report on B-related centers being another dominant source of recombination and acting as lifetime limiting defects in 4H–SiC epitaxial layers. Combining time-resolved photoluminescence (TRPL) measurement in near band edge emission and 530 nm, deep level transient spectroscopy, and minority carrier transient spectroscopy (MCTS), it was found that B related deep levels in the lower half of the bandgap are responsible for killing the minority carriers in n-type, 4H–SiC epitaxial layers when the concentration of Z1/2 is already low. The impact of these centers on the charge carrier dynamics is investigated by correlating the MCTS results with temperature-dependent TRPL decay measurements. It is shown that the influence of shallow B acceptors on the minority carrier lifetime becomes neutralized at temperatures above [Formula: see text] K. Instead, the deep B related acceptor level, known as the D-center, remains active until temperatures above [Formula: see text] K. Moreover, a correlation between the deep level concentrations, minority carrier lifetimes, and growth parameters indicates that intentional nitrogen doping hinders the formation of deep B acceptor levels. Furthermore, tuning growth parameters, including growth temperature and C/Si ratio, is shown to be crucial for improving the minority carrier lifetime in as-grown 4H–SiC epitaxial layers.

We demonstrate that the multi-photon absorption edge transient-current technique (edge-TCT) can be used to three-dimensionally map the impact of defect distributions on device characteristics in situ inside the bulk of silicon carbide devices. A ∼5 μm wide defect-rich layer induced by proton irradiation at a depth of ∼27 μm was investigated in 4H-SiC samples and compared to the pristine case. Edge-TCT enables mapping of the position of the implantation peak as well as to identify the space charge polarity around the implanted region. The edge-TCT results are compared to Monte Carlo simulations of the proton irradiation that were verified by luminescence measurements and TCAD-based device simulations. In result, edge-TCT is found to be capable of distinguishing different device regions due to its charge sensitivity and directly visualizing space charge regions, facilitating calibration of charge carrier distribution models in semiconductor devices.

Using positive muons as local probes implanted at low energy enables gathering information about the material of interest with nanometer-depth resolution (low-energy muon-spin-rotation spectroscopy, LE μSR). In this work, we leverage the capabilities of LE μSR to perform a detailed investigation of the widely studied yet poorly understood SiO 2 -SiC interface. Thermally oxidized samples are investigated before and after annealing in nitric oxide (NO) and argon (Ar) environment. Thermal oxidation is found to result in structural changes both in the SiC crystal close to the interface and at the interface itself, which severely degrade the transport properties of charge carriers. Annealing in NO environment is known to passivate the defects leading to a reduction of the density of interface traps (D it ); LE μSR further reveals that the NO annealing results in a thin layer of high carrier concentration in SiC, extending to more than 50 nm depending on the annealing conditions. From our measurements, we see indications of Si vacancy (V Si ) formation in SiC after thermal oxidation. Following NO annealing, nitrogen occupies the V Si sites, leading to the well-documented reduction in D it and, at the same time, creating a charge-carrier-rich region near the interface. The LE μSR technique sheds light on the near-interface region in the SiO 2 -SiC system, which is challenging to access using other techniques. By comparing the LE μSR data from a sample with known doping density, we perform a high-resolution quantification of the free carrier concentration near the interface after NO annealing and discuss the origin of the observed near-surface variations. Finally, the depletion of carriers in a MOS capacitor in the region exactly below the interface is demonstrated using LE μSR. The NO-annealed sample shows the narrowest depletion region, likely due to the reduced density of interface traps and the charge-carrier-rich region near the interface. Our findings demonstrate the many benefits of LE μSR to study critical regions of semiconductor devices that have been inaccessible with other techniques, while simultaneously retaining both nanoscale-depth resolution and a nondestructive approach.