SECOND-HARMONIC GENERATION IN SIC POLYTYPES
SECOND-HARMONIC GENERATION IN SIC POLYTYPES
复制标题
SIC 多型体中的二次谐波产生
DOI：
--
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发表时间：
1997
期刊：
影响因子：
--
通讯作者：
B. Segall
中科院分区：
文献类型：
--
作者：
S. Rashkeev;W. Lambrecht;B. Segall
A first-principles study of the frequency-dependent second-harmonic generation (SHG) coefficients of various SiC polytypes $(2H$, $4H$, $15R$, $6H$, and $3C)$, a group spanning the complete range of ``hexagonality,' was carried out. It uses a recently developed computational approach based on the self-consistent linear muffin-tin orbital band-structure method, which is applied using the local-density approximation to density-functional theory with a simple a posteriori gap correction. The susceptibilies are obtained in the independent-particle approximation, i.e., without local-field effects. The zero-frequency limits of the ratio ${ensuremath{chi}}_{333}^{(2)}/{ensuremath{chi}}_{311}^{(2)}$ for the noncubic polytypes were found to be in excellent agreement with those obtained by the pseudopotential method (and in disagreement with simple geometric predictions), while the magnitudes of the individual components themselves were found to be smaller than the values earlier calculated. The spectral features of the full ${ensuremath{chi}}^{(2)}(ensuremath{-}2ensuremath{omega},ensuremath{omega},ensuremath{omega})$ for $2H$ are found to differ markedly from those of the other polytypes. The spectra in the series of decreasing degree of hexagonality $(4H$, $15R$, and $6H)$ gradually approach those for the zinc-blende $(3C)$ form. The independent tensorial components appearing in the rhombohedral but not in the hexagonal forms are found to be about a factor 6 smaller than the other ones. An analysis of the SHG spectra in terms of $ensuremath{omega}$ and $2ensuremath{omega}$ resonances and individual band-to-band contributions is presented. It is suggested that second-harmonic generation spectra have an advantage over linear optical spectra for probing the electronic structure, particularly for the region within a few eV of the band edges in that they exhibit more detailed fine structure. That results from the sign variations in the products of matrix elements occurring in the SHG.
A first-principles study of the frequency-dependent second-harmonic generation (SHG) coefficients of various SiC polytypes $(2H$, $4H$, $15R$, $6H$, and $3C)$, a group spanning the complete range of ``hexagonality,' was carried out. It uses a recently developed computational approach based on the self-consistent linear muffin-tin orbital band-structure method, which is applied using the local-density approximation to density-functional theory with a simple a posteriori gap correction. The susceptibilies are obtained in the independent-particle approximation, i.e., without local-field effects. The zero-frequency limits of the ratio ${ensuremath{chi}}_{333}^{(2)}/{ensuremath{chi}}_{311}^{(2)}$ for the noncubic polytypes were found to be in excellent agreement with those obtained by the pseudopotential method (and in disagreement with simple geometric predictions), while the magnitudes of the individual components themselves were found to be smaller than the values earlier calculated. The spectral features of the full ${ensuremath{chi}}^{(2)}(ensuremath{-}2ensuremath{omega},ensuremath{omega},ensuremath{omega})$ for $2H$ are found to differ markedly from those of the other polytypes. The spectra in the series of decreasing degree of hexagonality $(4H$, $15R$, and $6H)$ gradually approach those for the zinc-blende $(3C)$ form. The independent tensorial components appearing in the rhombohedral but not in the hexagonal forms are found to be about a factor 6 smaller than the other ones. An analysis of the SHG spectra in terms of $ensuremath{omega}$ and $2ensuremath{omega}$ resonances and individual band-to-band contributions is presented. It is suggested that second-harmonic generation spectra have an advantage over linear optical spectra for probing the electronic structure, particularly for the region within a few eV of the band edges in that they exhibit more detailed fine structure. That results from the sign variations in the products of matrix elements occurring in the SHG.