Resonant photothermal bending spectroscopy at variable temperature 25–150 °C and its application to hydrogenated microcrystalline silicon films

Abstract

Resonant photothermal bending spectroscopy (RPBS) at various measurement temperatures has been developed for estimating absorption coefficient (α) spectra of thin film semiconductors. The experimentally obtained sensitivity of RPBS was about ten times larger than nonresonant PBS. In vacuum, this technique has been applied to estimate the α spectrum of hydrogenated microcrystalline silicon (μc-Si:H) films at the measurement temperatures from 25 to 150 °C. It is demonstrated that the temperature coefficient of an indirect optical absorption at 1.2–1.8 eV caused by Si microcrystallite is almost the same as that of single crystalline silicon, and the temperature coefficient of below-gap absorption intensity is negative. The reason for the negative temperature coefficient and the energy level of the localized state resulting in the below gap absorption are discussed.

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 properties of microcrystalline 3C–SiC:H films measured by resonant photothermal bending spectroscopy

“…Fig. 1 shows a schematic illustration of the resonant-PBS system [2,[5][6][7]. An edge of the sample was fixed to a holder in a specially designed optical cryostat.…”

“…Resonant photothermal bending spectroscopy (resonant-PBS) [2] is a kind of photothermal spectroscopy, such as photoacoustic spectroscopy (PAS) and photothermal deflection spectroscopy (PDS) [3,4]. The resonant-PBS has an advantage which is measurable in a vacuum.…”