Application Note: Raman Microscope Probes Semiconductor Defects

Using Raman microscopy to study flaws in the crystal structure of semiconductors could lead to better epitaxial growth processes that would make the materials more energy efficient when used in electronic devices.

Using a Raman microscope from Renishaw PLC, professor Noboru Ohtani of Kwansei Gakuin University has identified a potential cause of one kind of defect in 4H-SiC, a form of silicon carbide: During physical vapor transport, nitrogen enrichment near the crystal-seed interface is associated with compressive stress parallel to the interface.

Professor Noboru Ohtani of Kwansei Gakuin University with an inVia Raman microscope. Courtesy of Renishaw.

Additionally, temperature gradients, which are a primary driving force for crystal growth, can lead to plastic deformation of the crystals during the growth and cooling processes. This deformation results in residual stresses when the crystals are cooled to room temperature.

Ohtani and colleagues measured the spatial variation of stresses in the crystals using Renishaw's inVia confocal Raman microscope. The group also uses high resolution x-ray diffraction to characterize stress distribution. Raman microscopy provides complementary information to the x-ray data but with much higher spatial resolution.

"The key benefit is the ultrahigh-speed data acquisition system, which results in a higher sensitivity to measuring stresses in the materials compared to other Raman systems," Ohtani said.

One goal of Ohtani's group is to develop crystal growth processes that can produce large, ultrahigh-quality silicon carbide epitaxial wafers. The researchers recently published findings in Materials Science Forum (doi: 10.4028/www.scientific.net/MSF.821-823.90).