Sub-bandgap optical absorption spectroscopy of hydrogenated microcrystalline silicon thin films prepared using hot-wire CVD (Cat-CVD) process

Abstract

Hydrogenated microcrystalline silicon (Ac-Si:H) thin films with different silane concentration (SC) have been prepared using the HW-CVD technique. Dual beam photoconductivity (DBP), photothermal deflection spectroscopy (PDS), and transmission measurements have been used to investigate the optical properties of the Ac-Si:H films. Two different sub-bandgap absorption, a(hm), methods have been applied and analyzed to obtain a better insight into the electronic states involved. A good agreement has been obtained in the absorption spectrum obtained from the PDS and DBP measurements at energies above the bandgap. Differences between PDS and DBP spectra exist below the bandgap energy where DBP spectra always give lower a(hm) values and show a dependence on the SC. For some films, differences exist in the a(hm) spectra when the DBP measurements are carried out through the film and substrate side. In addition, for some films, there remains fringe pattern left on the spectrum after the calculation of the fringe-free absorption spectrum, which indicates structural inhomogeneities present throughout the film. D

Reversible and irreversible effects after oxygen exposure in thick (>1 μm) silicon films deposited by VHF-PECVD on glass substrates investigated by dual beam photoconductivity

“…On the other hand, the SiO x films are highly transparent in the optical wavelength range of interest so they have negligible effect on the data in our experimental methods, in particular steady-state photonconductivity and defect spectroscopy with the DBP method. Sub-bandgap absorption coefficient spectra obtained using DBP are a powerful tool to investigate the changes in the occupation of defect states in the light-soaked and annealed states of a-Si:H films [11] and are also very sensitive to study bulk defects in c-Si:H films [12]. Preliminary results obtained with the DBP method indicated that reversible and irreversible changes created by water and (or) oxygen exposure can be detected by the changes in the sub-bandgap absorption coefficient spectrum [13].…”

Humidity Sensing Properties of CdS Nanoparticles Synthesized by Chemical Bath Deposition Method

“…Among these deposition methods, CBD technique is one of the least expensive and simplest methods, which makes it very attractive to obtain reproducible and uniform CdS films . On the other hand, the presence of moisture is an important parameter for degradation on the conversion efficiency and lifetime of CdS solar cells . Therefore, the effect of the humidity level should be considered during the lamination process …”

Effect of Assisted-Ion-Beam Gases on the Structure of Amorphous Silicon Thin Films Prepared by Ion-Beam-Assisted Sputtering

“…The absorption coefficient at low energy of 0.8 eV (α(0.8 eV)) is sensitive to the defect density of states in the gap of a-Si thin films, the lower the α(0.8 eV), the lower the defect density of states [12,13,18]. Figure 5 shows the α(0.8 eV) evolution of the a-Si:H thin films deposited with different assisted-ion beam gases.…”

“…Figure 6 shows the Eg of the a-Si thin films deposited with different assisted-ion beam gases [18,19]. It was observed that the Eg of a-Si:H thin films deposited without assisted-ion-beam and with…”