MICROSCOPY AND IMAGING
Figure 1: Raman imaging of a 150 mm SiC wafer. A: Raman spectra of two components that diff er in the doping-sensitive A1
E2 A.
(LO) mode (ca. 990 rel. cm-1).
B: Diff erent doping concentration (blue) compared to the bulk wafer area (red) color coded according to (A). C: Distribution of stress-sensitive
(high) peak (776 rel. cm-1), revealing compressive peak shifts in the wafer’s
center and tensile shifts toward its edge. (D) Warpage of the SiC wafer with height varia tions of up to 40 µm.
B.
feature was used to generate a high- resolution 3D map of an FR-source in GaN (Fig. 2A). The obtained Raman spectra were automatically analyzed to detect spectral diff erences and identify components. Three diff erent components were found for GaN: The relatively relaxed GaN (red) and two stressed forms (blue, green) within the FR-source. Next, PL signals were analyzed, and the visualized emission peak position (Fig. 2B) shows a diff erent PL fi ngerprint for the FR-source compared to the overall sample, confi rming the alterations in its semiconducting properties.
C. D.
SUMMARY The examples shown demonstrate the utility of Raman imaging for characterizing compound semiconductors. The alpha300 Raman system set up for large-area scanning measured doping, stress and topography in a 150 mm SiC wafer and another alpha300 Raman microscope carried out a correlative Raman-PL measurement of GaN that visualized its composition and stress states in three dimensions. Researchers in semiconductor
to material stress and strain. In comparison to the overall wafer, more central regions were exposed to compressive stress while distal regions were subjected to relatively higher tensile stress (Fig. 1C). TrueSurface compensated for height variations within the sample and allowed the recording of the wafer’s topography and warpage (Fig. 1D) simultaneously along with the Raman spectral information.
CORRELATIVE RAMAN- PL IMAGING OF A FRANK-READ SOURCE IN GaN A a possible origin of stress in crystals, including crystalline semiconductors, is a Frank-Read source (FR-source). The term describes the dislocations and repeating wrapping patterns that result from deformations and alterations in a crystal lattice. These can be detected and located with Raman imaging. In photoluminescence (PL), photons excite electrons, then fall back to a
ground state and re-emit a photon at a longer emission wavelength which is characteristic for each material. For semiconductors, the PL-emitted light can serve as an indicator of its bandwidth, as the energy of excited electrons is reduced to the bandgap minimum in the relaxation process. Here, a WITec alpha300 Raman microscope equipped with the TrueComponent Analysis software
development rely on detailed, conclusive investigations such as these to achieve a comprehensive understanding of their materials and manufacturing processes. The WITec alpha300 line of Raman microscopes off er precise, versatile tools that can help accelerate their rate of advance. ■
For more information visit
https://raman.oxinst.com/
Figure 2: High- resolution 3D mapping of GaN with FR- source. A: Raman image generated using TrueComponent Analysis to identify GaN (red) and GaN stressed states (blue, green). B: The color-coded visualization of the photoluminescence (PL) peak position in GaN shows altered PL emission wavelength in the FR-source region.
www.scientistlive.com
35
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60
