Spatial characterization of Doped Sic Wafers
- PDF / 253,106 Bytes
- 5 Pages / 414.72 x 648 pts Page_size
- 67 Downloads / 195 Views
3
1019 cm" .
Significant coupling of the A1 longitudinal optical
(LO) phonon to the plasmon mode was observed. The position of this peak shows a direct correlation with the carrier concentration. Examination of the Raman spectra from different positions on the wafer yielded a rudimentary spatial map of the carrier concentration. This data is compared with a resistivity map of the wafer. These results suggest that Raman spectroscopy of the LO phonon-plasmon mode can be used as a noninvasive, in situ diagnostic for SiC wafer production and substrate evaluation. INTRODUCTION Silicon carbide (SiC) has recently been recognized as an important material for a wide variety of high-power and high-temperature electronic applications. SiC exhibits a large number (250) of polytypes with different structural and physical properties. 1The polytypes have the same chemical composition but exhibit different crystallographic structures and stacking sequences along the principal crystal axis. Several important polytypes of SiC such as 4H- and 6H- have C61 crystallographic symmetry. In the a-direction 4H- and 6H-SiC are almost identical (< 1% change); however, the 4H- polytype consists of 4 units in the c-direction and the 6Hconsists of 6 units. Different polytypes have different band gaps, electron mobilities, and other physical properties; for example, 4H-SiC has attracted significant attention due to its high electron mobility and excellent thermal properties. Recently high quality wafers of both 4H- and 6H-SiC have been grown. 2 Wafers of SiC are also a promising substrate for nitride semiconductor growth due to their compatible lattice structure and similar thermal expansion coefficients. There have been several previous experimental studies of the one-phonon Raman spectra of SiC. 3 The importance of polytypes on the one phonon Raman spectra of SiC was first noted 297 Mat. Res. Soc. Symp. Proc. Vol. 512 ©1998Materials Research Society
by Choyke and collaborators. 4 Raman has been shown to be a valuable probe of SiC grown by a variety of techniques. 3 In this study, we have performed Raman scattering measurements at room temperature for heavily doped 4H-SiC and 6H-SiC wafers. The wafers of SiC were n- type, nitrogen doped, with concentrations ranging from 2.1 x
1018
cm-3 to 1.2 x 1019 cm-3. A semi-insulating wafer of
4H-SiC was also examined as a reference. Nitrogen is well established as a donor in SiC. 1 Significant changes were observed in the shape and position of the A 1(LO) phonon as a function of doping concentration. The changes in peak position, spectral shape, and width of the AI(LO) phonon are attributed to plasmon-phonon coupling. The experimental Raman lineshape was compared with theory. We have exploited the plasmon-phonon coupling to estimate the spatial dependence of the carrier concentration across the SiC wafer. Unlike electrical conductivity measurements, which involve the attachment of an electrical contact to the material, Raman spectroscopic determination of carrier concentrations is nondestructive an
Data Loading...
