Silicon carbide is a highly promising material for high frequency, high temperature and high power applications in electronic devices. However, since there are a wide variety of potential extended defects in the material, the commercialization of many SiC-based electronic devices has been challenging.
To improve the performance of SiC, numerous studies of the formation and the propagation of defects during crystal growth have been carried out. Though the results have resulted in major advancements in the technology facilitating the commercialization of SiC, the mechanisms behind formation and proliferation of extended defects has not yet been fully understood.
Within SiC there is a wide array of different extended defects. Three of the most detrimental of these are threading dislocations, in-grown stacking faults and recombination-inducted stacking faults (RISFs).
RISFs have been difficult to manage as they expand during device operation and lead to continuous increases in the turn-on voltage of bipolar devices, such as pin diodes. The expansion is induced by the recombination of free carriers near the RISFs.
Defect Identification Methods
Electroluminescence can be used to identify the extended defects, as RISFs emit in the violet at 2.89eV (430nm). The partial dislocations that bound the faulted regions also emit in the red at 1.8 eV (690 nm).
In 4H-SiC, partial dislocations were observed to develop a green luminescence along the carbon-core partial dislocations during device operation. Even if the RISFs are contracted through annealing, the emission is retained.
It can be seen in Video 1 that the RISFs expand along several current injection times, and the green luminescent centers move along the partial dislocations. This implies that point defects like boron impurities can be induced to move within SiC under carrier injection, as well as RISFs.
Video 1. Silicon Carbide Defect Characterisation
Photon etc's IMA-EL™ hyperspectral imager is specifically designed for studying electroluminescent materials. The instrument was used to obtain spatial and spectral information about the defects simultaneously. This technique enabled rapid and accurate identification of the type of defects that contribute to the green emission in 4H-SiC.
After successive periods of device operation and the subsequent annealing in nitrogen atmosphere at 700ºC to contract the RISFs, the electroluminescence imaging of the SiC pin diode was performed as shown in Figure 1a.
After the RISFs were expanded again, the electroluminescence from the device was collected in the 400-780nm spectral range, with a step of 2nm and an exposition time of 30s. The separation of the different classes of defects was allowed by the single monochromatic images collected with IMA.
Figure 1b shows the peak emission of RISFs, centered at 424nm, and Figure 1c and 1d show the partial dislocations at 534nm and 720nm. The spectral response of the two regions labelled with “1” and “2” as shown in Figure 2 confirmed that the PDs show a similar sharp emission at 424nm due to the RISFs, and a broader emission at 530-540nm.
By combining spatial and spectral information it was possible to attribute the latter emission to mobile boron impurities.
Figure 1. Real color EL (a) and hyperspectral EL images (b-d) after annealing
Figure 2. EL spectra of regions 1 and 2
It was possible to effectively identify the luminescence band of the various classes of faults using the IMA-EL™ hyperspectral imager from Photon etc. This will enable a better understanding about the formation of defects and their propagation in SiC materials.
About Photon etc.
Photon etc. offers state-of-the-art photonic and optical research instrumentation, from laser line tunable filters to widefield and microscopy hyperspectral imaging systems. Its patented spectral imaging and optical sensing technologies provide solutions for a wide variety of scientific and industrial applications. From material analysis to medical imaging, Photon etc.’s expertise and spirit of innovation allow the exploration of uncharted territories.
Photon etc. aims to provide each researcher, engineer and technician with access to the latest innovations in optical and photonic instrumentation. As pioneers in Bragg-based hyperspectral imaging, Photon etc. offers state-of-the-art instruments, driven by its clients’ desires to surpass limitations in measurement and analysis.
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This information has been sourced, reviewed and adapted from materials provided by Photon etc.
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