Optical properties of hydrogenated amorphous silicon

Abstract

A detailed study of the optical properties of sputtered hydrogenated amorphous silicon films with varying hydrogen concentration is presented here. The energy dependence of the absorption coefficient is looked into, in detail, from a point of view of understanding the well known Tauc rule and the alternate relations being proposed in recent years. Spectroscopic and band-structural models like Wemple–Didomenico and Penn are then utilized to analyze the optical parameters near the band-gap region of the wavelength spectra. Extensive comparisons of our results are made with those of sputtered a-Si:H films of other workers, glow discharge prepared a-Si:H, chemically vapor deposited and evaporated a-Si, and also crystalline silicon. The similarities in the variation of the optical properties of a-Si:H with increasing hydrogen concentration (or decreasing measurement temperature) to that of crystalline silicon with decreasing measurement temperature lead us to interesting conclusions. Thus, it seems that decreasing disorder (topological or thermal) in a-Si:H is equivalent to decreasing thermal disorder in c-Si, at least as far as the disorder-optical property relationships are concerned.

On-Chip Integrated Photonic Devices Based on Phase Change Materials

“…These laser-based systems can crystallize and re-amorphize the silicon on the nanosecond time scale, and this process can be reversibly switched without any deformation. The change in refractive index and absorption coefficient brought about due to the silicon changing phase is not significant at the wavelength of 1.55 µm [73]. However, the difference becomes comparatively large as the wavelength shortens to the visible regime, as shown in Figure 4.…”

Photo-excited hot carrier dynamics in hydrogenated amorphous silicon imaged by 4D electron microscopy

“…Briefly, infrared laser pulses (1030 nm, 300 fs), generated by a Clark-MXR fiber laser system, are split to generate green (515 nm) and UV (257 nm) pulses; the green is focused onto the sample as both the photo-excitation and the clocking pulse, while the UV pulse is focused onto the photocathode to generate ultrashort electron pulses. The diameter of the pump is ~60 µm, and the fluence at 515 nm (photon energy 2.4 eV) for data reported in the main text is ~20 µJ/cm 2 with the pulse repetition rate at 25 MHz, corresponding to a peak carrier concentration ~3 × 10 18 cm −3 28 . The data for a fluence of ~67 µJ/cm 2 (repetition at 5…”

Revealing Structural Disorder in Hydrogenated Amorphous Silicon for a Low‐Loss Photonic Platform at Visible Frequencies

“…[ 1,2 ] Compared to conventional amorphous silicon (a‐Si), a‐Si:H is used in silicon platforms in the infrared region, since the hydrogen passivates the dangling bonds which blueshifts the bandgap. [ 3,4 ] Additionally, the inherent properties of silicon have been continuously investigated in order to enhance the optoelectrical properties for uses in silicon photonics. For example, the bandgap of hexagonal silicon‐germanium is found to efficiently emit light, suggesting that it could be applied to light‐emitting photonic technology.…”