Band Structure of SiC Overview

From the theoretical calculations as well as the optical measurements, it is known that all the polytypes have the valence band maximum at the zone centre (T-point). However, the location of the conduction band minimum in k-space depends on the polytype, for example, X-point for 3C- and K-point for 2H-SiC. All the polytypes, studied thus far, have indirect bandgaps, which increase monotonically with the hexagonality of the polytypes h, from Eg = 2.417 eV for 3C-SiC (h=0) to Eg = 3.33eV for 2H-SiC (h= 1). TABLE 1 shows the values of the hexagonality, the indirect bandgap, and its temperature coefficient for various typical polytypes [2-5]. 

TABLE 1 Hexagonalities, observed minimum indirect and direct bandgaps at 4K and their temperature 

Polytype Jagodzinski notation Hexagonality h Minimum bandgap eV dEgin/dT 

The cubic modification (3C-SiC) is the only SiC with zinc blende structure. The band structure of 3C-SiC has been calculated theoretically by Kobayashi [1], and estimated from optical absorption and reflection [6], luminescence [7], soft X-ray emission [8] and X-ray photoelectron [9] spectra. 

Hoechst and Tang [29] investigated the band structure with synchrotron radiation by angular resolved valence-band photoemission spectroscopy, and found good agreement in the band structure mapped along T-X with theoretical calculations by Lubinsky et al [19]. 

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As described in Section 1, there exist many theoretical approaches to calculating electronic structure of solids, and most of them have also been applied to lanthanides. In this section, we shall briefly overview some of the most widely used, focusing however on the SIC-LSD, in both full and local implementations, as this is the method of choice for most of the calculations reported in this chapter. The simplest approach to deal with the f electrons is to treat them like any other electron, that is, as itinerant band states. Hence, we start our review of modem methods with a brief account of the standard LDA and its spin-polarized version, namely the LSD approximation. We also comment on the use of LSD in the cases, where one restricts the variational space by fixing the assumed number of f electrons to be in the (chemically inert) core ( f-core approach). Following this, we then briefly overview the basics of other, more advanced, electronic stmcture methods mentioned in Section 1, as opposed to a more elaborate description of the SIC-LSD method. 

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