Properties of Silicon Carbide
Fully indexed with over 1000 references to published and unpublished sources, this book draws together the expert knowledge of numerous researchers from around the world to completely characterize the SiC system.
TABLE OF CONTENTS Properties of Silicon Carbide
Chapter 2: Optical and Paramagnetic Properties
2.1 Optical Absorption and Refractive Index of SiC
G.L. Harris
February 1995
A INTRODUCTION
This Datareview outlines the data on optical absorption and refractive index in the various polytypes of SiC. The optical transitions give rise to the characteristic colour of each polytype. Values for both the ordinary and extraordinary refractive indices versus wavelength are given.
B OPTICAL ABSORPTION
The optical absorption in SiC can, in general, be characterized by intraband and interband absorption components. The interband transitions in n-type polytypes other than 3C are responsible for the well-known colours of nitrogen-doped samples. The intraband absorption is of the free-carrier type and results in sub-bandgap transitions that are found in most forms of SiC. Biedermann [1] has measured the optical absorption bands at room temperature along the E ? c and E ? c directions for 4H, 6H, 8H and 15R n-type SiC. These are the most anisotropical used types of SiC. These polytypes are uniaxial and are strongly dichroic [2]. The surface is normally perpendicular to the c-axis. This gives rise to the green colour in 6H, the yellow colour in 15R, and the green-yellow colour in 4H polytypes. These bands responsible for the colour are attributed to optical transitions from the lowest conduction band to other sites of increased density of states in the higher, empty bands [3], thus producing the various colours of nitrogen-doped 6H, 15R and 4H. Cubic SiC changes form a pale canary yellow to a greenish yellow when the material is doped.
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