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  • Other Semiconductors

Hyperspectral Electroluminescence Characterization of Silicon Carbides Defects

Silicon carbide (SiC) is a very promising material for high temperature, high frequency and high-power applications in electronic devices. However, the commercialization of many SiC-based electronic devices has been challenging due to the presence of a variety of extended defects. In order to improve the performance of SiC, studies about the formation and the propagation of defects during crystal growth have been carried out. Although the results contributed to major advancements in the technology, facilitating the commercialization of these materials, the formation and proliferation of extended defects have not been fully understood yet.

There is a wide array of extended defects within SiC, three of the most detrimental are threading dislocations, ingrown stacking faults and recombination-induced stacking faults (RISFs). In particular, RISFs have been difficult to manage, because 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 through the recombination of free carriers near the RISFs. Understanding the mechanism for their motion is tantamount to their mitigation.

Electroluminescence (EL) is commonly used to identify the extended defects: RISFs emit at 2.89 eV (430 nm) and the partial dislocations (PDs) that bound the faulted regions are known to emit at 1.8 eV (690 nm). In 4H-SiC, partial dislocations also developed a green luminescence along the carbon-core partial dislocations during device operation. This emission is retained, even if the RISFs are contracted via annealing. IMA, Photon etc.’s global hyperspectral imager, was used to acquire spectral and spatial information of the defects simultaneously. IMA consists of an optical microscope coupled with a source meter, probes and a hyperspectral filter based on volume Bragg gratings. Hyperspectral EL imaging allowed a rapid and accurate identification of the class of defects that contributes to the green emission in 4H-SiC.

The video below shows how the RISFs expand along various current injection times, and how the green luminescent centers move along the partial dislocations. This implies that not only RISFs do move under carrier injection within SiC, but that point defects such as boron impurities, can also be induced to move under such conditions.

Silicon Carbide Defect Characterization

This video shows how various types of defects in SiC can easily be detected using electroluminescence maps obtained with Photon etc’s hyperspectral imaging system, IMA. Offering spectrally resolved images, Photon etc’s hyperspectral imaging technology improves advanced material development capacities.

a) Real color EL of SiC pin diode and b-d) monochromatic EL images extracted from the hyperspectral data, after annealing, e) EL spectra of regions one and two (see a)). Adapted from [1].
Fig. 1 - a) Real color EL of SiC pin diode and b-d) monochromatic EL images extracted from the hyperspectral data, after annealing, e) EL spectra of regions one and two (see a)). Adapted from [1].

EL imaging of the SiC pin diode was performed after successive periods of device operation and subsequent annealing in nitrogen atmosphere at 700 ºC to contract the RISFs (Fig. 1 a) [1]. Following the expansion of the RISFs, the EL from the device was collected from 400 nm to 780 nm, with 2 nm step and an exposition time of 30 s. The single monochromatic images collected with IMA allowed the separation of the classes of defects. In particular, Fig. 1 b shows the peak emission of RISFs, centered at 424 nm, and Fig. 1 c-d the partial dislocations at 534 nm and 720 nm. The spectral response of the two regions labelled with “1” and “2” (Fig. 1 e) confirmed that the PDs show a similar sharp emission at 424 nm due to the RISFs, and a broader emission at 530-540 nm. Combining spectral and spatial information, it was possible to attribute the latter emission to mobile boron impurities.

Photon etc.’s hyperspectral imager was paramount to identify the luminescence band of the various classes of faults, and will empower a better understanding about the formation of defects and their propagation in SiC materials.

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[1] Caldwell, J. D., Giles, A., Lepage, D., Carrier, D., Moumanis, K., Hull, B. A., Stahlbush, R. E., Myers-Ward, R. L., Dubowski, J. J., & Verhaegen, M. (2013). Experimental evidence for mobile luminescence center mobility on partial dislocations in 4H-SiC using hyperspectral electroluminescence imaging. Applied Physics Letters, 102(24), 242109.

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