Unipolar silicon carbide (SiC) semiconductors are widely used in commerce, but their operations are limited by a compromise relationship between the breakdown voltage and the specific resistance of the drift layer, or resistance to specific pass state. Including a superjunction structure, which refers to an arrangement of n and p layers in trenches in the drift layer, or allowing bipolar operation in the device overcomes this unipolar limitation. Bipolar operation results in a strong reduction in the pass resistance by inducing a modulation of conductivity in the drift layer. But bipolar operation is not without drawbacks. Conduction and switching losses in bipolar devices must be carefully balanced.
P-type contact layers in semiconductors are typically formed by doping with aluminum (Al). Al doping can be obtained in two ways: by epitaxial or ionic implantation. Epitaxial growth involves the layer-by-layer deposition of semiconductor materials on a substrate, while ion implantation involves bombarding the semiconductor layers with high-energy charged particles. But ion implantation leads to the formation of deep defects in semiconductor layers, which could have a critical effect on the modulation of conductivity.
In a recent study published in Physica Solidi (b) status, Japanese researchers have studied the depth distribution of defects in bipolar SiC diodes formed by doping with Al. âOur results will help in the optimal design of SiC power devices, which will soon be used in electric vehicles, trains, etc. These results will ultimately help improve the performance, size and energy consumption of traction systems in vehicles and trains. said Associate Professor Dr Masashi Kato of the Nagoya Institute of Technology, who led the study.
To study the in-depth distribution of the defects, the research team fabricated two SiC PiN diodes with Al-doped p layers, one by epitaxial growth and the other by ion implantation. They then studied the distribution of defects in the two diodes using conventional “deep level transient spectroscopy” (DLTS) and characterized its properties using cathodoluminescence (CL). They found that the deposition of p-type layer by epitaxial growth did not cause damage in the adjacent n-type layers, but that the growth showed slight instability which led to the formation of deep level defects. The specific pass-through resistance of this diode was also low, thanks to the effects of modulating conductivity.
For the diode formed by ion implantation, however, the researchers found that the Al doping achieved a high specific pass-state resistance without influencing the modulation of the conductivity. In addition, the researchers observed that the defects of the semiconductor device penetrated down to a minimum of 20 Âµm from the implantation area. âOur study shows that ion implantation in bipolar SiC devices must be processed at least 20 Âµm from active regions,â explains Dr. Kato.
The low power consumption of SiC power devices means that they will be essential in the future as climate change intensifies and the fossil fuel crisis worsens. Rapidly improving semiconductor technology so that it can take its rightful place on the world stage is of paramount importance. With strong results like this to inform future research and manufacturing, we can realize this future sooner than expected!
No disassembly necessary: ââNon-destructive method to measure the service life of the SiC support
Shuhei Fukaya et al, Depth distribution of defects in SiC PiN diodes formed using ion implantation or epitaxial growth, solid physical status (b) (2021). DOI: 10.1002 / pssb.202100419
Provided by Nagoya Institute of Technology
Quote: Distribution of defects in SiC diodes implanted in ions (2021, November 18) retrieved on November 18, 2021 from https://techxplore.com/news/2021-11-defect-ion-implanted-sic-diodes.html
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