Optical Absorption Spectra of Hydrogenated Microcrystalline Silicon Films by Resonant Photothermal Bending Spectroscopy

Abstract

A resonant photothermal bending spectroscopy (PBS) is demonstrated for the measurement of absorption coefficient spectra in hydrogenated microcrystalline silicon (µc-Si:H) and hydrogenated microcrystalline cubic silicon carbide (µc-3C–SiC:H) films. The resonant vibration technique utilized in PBS establishes the sensitivity as αd∼5×10-5 in a vacuum measurement. Appling resonant PBS to µc-Si:H films, a new extra absorption coefficient αex spectrum is observed from 0.6 to 1.2 eV. The αex spectrum has a peak at ∼1.0 eV, and the localized states inducing the αex are located ∼0.35 eV below the conduction band edge of µc-Si:H. A possible explanation for the observed localized state is that an oxidation produces weak bonds at the grain boundaries and/or amorphous silicon tissues. In µc-3C–SiC:H film, an optical band-gap energy of ∼2.2 eV was demonstrated assuming an indirect optical transition. The temperature coefficient of the optical band-gap energy was ∼2.3×10-4 eV K-1. The αex spectrum of µc-3C–SiC:H film is plateau-shaped and its magnitude is in accord with an increase in grain size.

A study of absorption coefficient spectra in a-Si:H films near the transition from amorphous to crystalline phase measured by resonant photothermal bending spectroscopy

“…2 by the solid line with solid circles. Those of a conventional a-Si:H film with a bandgap energy of 1.75 eV and for a microcrystalline Si film [4,5] are also indicated by solid and dashed lines, respectively. It is found that there exists extra absorption with interference fringes at 1.2-1.6 eV in the widegap a-Si:H film, an absorption coefficient a being about 10 2 cm À1 at a photon energy of 1.3 eV.…”

“…This technique is a kind of photothermal spectroscopy, such as photoacoustic spectroscopy (PAS) and photothermal deflection spectroscopy (PDS) [6]. In brief [4,5], when light illuminates a bimorph sample constructed from a thin film semiconductor and a quartz glass substrate, a bending occurs in the sample because of thermal expansion of the film due to non-radiative recombination of photoexcited carriers. The magnitude of the bending is proportional to optical absorbance of the film.…”

“…We have previously suggested that resonant photothermal bending spectroscopy (resonant-PBS) [4,5] is a useful tool for evaluating optical absorption spectra of thin film semiconductors. In this study, we have tried to apply this technique to widegap a-Si:H [1,2] for the first time for estimating absorption coefficient spectra a.…”

Optical absorption spectra of perovskite thin films for defect estimation by photothermal bending spectroscopy

“…In this study, resonant-type PBS (resonant-PBS) [22][23][24][25] was employed for improving the sensitivity. Figure 1 shows a schematic illustration of the resonant-PBS system.…”

β-FeSi2as the bottom absorber of triple-junction thin-film solar cells: A numerical study

“…The light absorption coefficient of β -FeSi 2 has been given in our previous work. [9] The temperature coefficients of the bandgaps of a-Si, µc-Si, and β -FeSi 2 are 4.7×10 −4 eV/K, [24] 4.2×10 −4 eV/K, [25] and 3.1×10 −4 eV/K, [26] respectively. The Yunaz model [27,28] of the tunnel-recombination junction for simulating the triplejunction solar cell is employed.…”