Thermal evolution of the band edges of 6H-SiC: X-ray methods compared to the optical band gap

Abstract

The band gap of semiconductors like silicon and silicon carbide (SiC) is the key for their device properties. In this research, the band gap of 6H-SiC and its temperature dependence were analyzed with silicon 2p x-ray absorption spectroscopy (XAS), x-ray emission spectroscopy (XES) and resonant inelastic x-ray scattering (RIXS) allowing for a separate analysis of the conduction-band minimum (CBM) and valence-band maximum (VBM) components of the band gap. The temperature-dependent asymmetric band gap shrinking of 6H-SiC was determined with a valence-band slope of +2.45x10 -4 eV/K and a conduction-band slope of -1.334x10 -4 eV/K. The apparent asymmetry, e.g., that two thirds of the band-gap shrinking with increasing temperature is due to the VBM evolution in 6H-SiC, is similar to the asymmetry obtained for pure silicon before. The overall band gap temperature-dependence determined with XAS and non-resonant XES is compared to temperature-dependent optical studies. The core-excitonic binding energy appearing in the Si 2p XAS is extracted as the main difference. In addition, the energy loss of the onset of the first band in RIXS yields to values similar to the optical band gap over the tested temperature range.

The angular- and crystal-momentum transfer through electron–phonon coupling in silicon and silicon-carbide: similarities and differences

“…These small energetic changes in combination with the shift of the Si L 3 absorption edge point to a decrease in the band gap energy with temperature. A detailed discussion is beyond the scope of this paper and will be conducted elsewhere [46]. The changes in the features of the RIXS spectra with temperature will be dealt with in the following subsections.…”

“…We would like to point out that the feature appearing in the middle panel around 99 eV increasing for the 300-900°C is an indirect result of the shift of the valence band maximum with temperature shortly mentioned above. In a separate paper we analyze the band gap, the valence band maximum and conduction band minimum of 6H-SiC as a function of temperature [46]. The RIXS spectra indicated with C in the left panel of figure 1 do not seem to show this valence band maximum shift, but after zooming in one may recognize a small but nonnegligible shift in the valence band maximum as a function of temperature [46].…”

Strain analysis from M-edge resonant inelastic X-ray scattering of nickel oxide films

“…For more complex materials strain engineering provides an attractive alternative method for tailoring materials' properties beyond what is possible through doping or chemical substitution. 10,14 As combination of X-ray absorption and emission spectroscopy, Resonant Inelastic X-ray Scattering (RIXS), is specific for determining electronic structure properties such as the band gap, 15 covalent interactions, 16 potential energy surfaces 17 and excited states 18 with element-and oxidation-state specificity. In this report it will be shown that RIXS is also sensitive to changes in electronic structure due to induced strain.…”

SIMS and auger investigation of thin a-SiC and a-SiC:H films by Up-Down sputtering DC magnetron, impact on optical properties

“…They offer many potential applications in many kinds of optoelectronic devices, such as solar cells [2][3][4], temperature and gas sensors [5,6], protective coatings [1] full-color electroluminescent display [7], and light emitting diodes [5,[8][9]. By varying the carbon concentrations in a-SiC films, the optical gap (Eg) can be continuously tuned in a wide range, which makes it useful for devices design and performances [10], and thus the electrical and optical properties can be manipulated to better suit the application in photovoltaic heterojunction devices [8,11].…”