Tunable nonlinear absorption of hydrogenated nanocrystalline silicon

Abstract

Nonlinear absorption (NLA) of hydrogenated nanocrystalline silicon (nc-Si:H) has been investigated through the open aperture Z-scan method for the photon energy of the incident irradiance slightly less than the bandgap of the sample. NLA responses have been observed to be highly sensitive to the wavelength and intensity of the incident irradiance as well as to the bandgap of the sample, indicating greatly tunable NLA of nc-Si:H. The band tail of nc-Si:H appears to play a crucial role in such NLA responses.

Femtosecond laser materials processing of a-Si:H below the ablation threshold

“…Assuming a two photon absorption (TPA) coefficient of 1 nmW -1 [8] and a reflectivity of the a-Si:H layer of 63%, a deposited energy density of 2 kJcm -3 close to the surface region is derived. To benchmark this value thermal annealing experiments of co-deposited a-Si:H samples on c-Si substrates are conducted.…”

“…For nonlinear absorption, the intensity within the a-Si:H layer can be described by the following differential equation (1) [8]:…”

Nonlinear optical absorption tuning in Bi3.15Nd0.85Ti3O12 ferroelectric thin films by thickness

“…Thus, research advances in this field depend critically and primarily on the development of new materials with strong NLO capabilities and effective tailoring of their NLO properties. During the past years, many peculiar NLO materials, such as Au and Pt nanoparticles, [8][9][10] nanocrystalline Si and Si/SiO 2 multilayers, [11][12][13] graphene and graphene-doped polymer, 14,15 PMMA films, 16 and pyrrole methine, 17 have been widely investigated and demonstrated that their application field can be enormously extended by tailoring their NLO properties.…”

“…18,[21][22][23] The similar SA-to-RSA switching phenomenon has already been found in noble metal nanoparticles 8-10 and nanocrystalline Si films. [11][12][13] Generally, this switching phenomenon is considered to be the consequence of the competition between the ground-state excitation and the nonlinear absorption, which is critically dependent on the laser photon energy, the intensity of the incident radiation, and the band-gap energy of materials. [8][9][10][11][12][13] Nevertheless, our Z-scan experiment was performed at the fixed I 0 and k, which can eliminate the possible inducements of the laser.…”

“…Such a E g variation is large enough to permit the transformation process happening because the NLO absorption switching is critically sensitive to the energy variation even it is less than tens meV. 11,12 The mechanism for the influence of the E g on the switching is discussed as follows. In our previous work, the intermediate energy levels (i.e., defect states) have been demonstrated in BNT thin films.…”