Method for direct determination of the effective correlation energy of defects in semiconductors: optical modulation spectroscopy of dangling bonds

Journal ArticleThe optical modulation technique is used for direct determination of energy levels and the effective correlation energy U/eff of dangling-bond defects. With an accuracy of 0.1 eV we found for the dangling-bond defect in α-Si:H, f/e f f=0.5 eV; in α-As2S3, £/e f f= - 1.0 eV; in As2Se3, Ueff = -0.7 eV; and in trans-(CH)x, Ueff=0.95 eV

Hot-carrier thermalization in amorphous silicon

Journal ArticleThermalization of photoinduced carriers in a-Si and α-Si:H was studied with use of sub-picosecond-pump and probe techniques with parallel and perpendicular polarizations. The underlying process was identified as hot-carrier absorption whose cross section increases with the carrier excess energy. The energy dissipation rate in α-Si is ≈ 0.5 eV/ps (≈hv 2 phonon) and is less than 0.1 eV / ps in a-Si:H; Frohlich interaction with polar phonons can explain this smaller rate. A photoinduced dichroism associated with polarization memory was observed

Picosecond dynamics of carriers in amorphous semiconductors

Journal ArticleUsing time resolved photoinduced absorption with subpicosecond resolution we studied hot carrier thermalization followed by deep trapping and recombination in a-Si, a-Si:H, a-Si:F, a-Si:H:F and a-As2Se3. In a-Se and a-As2S3_xSex (0.25 < x < 0.75) the observed relaxations were attributed to geminate recombination

Optical picosecond studies of carrier thermalization in amorphous silicon

Journal ArticleThermalization of photogenerated hot carriers in a-Si, a-Si:H and a-Si:H:F was studied using the pump and probe method with subpicosecond resolution. The process is optically observable because the absorption cross-section of the hot carriers depends on their excess energy. It was found that the energy dissipation rate to phonons is the maximum possible in a-Si while in a-Si:H it is slower and can be described by Frohlich interaction with polar phonons

Steady-state photomodulation spectroscopy of a-Si:HI a-SiNx:H multilayer structures

The steady-state photomodulation (PM) spectrum and its temperature dependence were studied in a-Si:H/a-SiNx:H multilayer structures (MLS). We found that the photocarrier properties in MLS with Si sub layer thickness ds &lt; 20 A are dominated by band-tail broadening resulting from increase in disorder. The PM spectrum for MLS with ds &gt; 20 A is mainly due to interfacerelated defects; because of its similarity with the PM spectrum of P-doped a-Si:H we identify the defects as charged dangling bonds

Beitrag zum Problem der heterosynaptischen Facilitation in Aplysia californica

1. Heterosynaptic facilitation (H.S.F.) of single neurons in the central nervous system of Aplysia can be repeated virtually indefinitely, provided sufficient time is allowed for recovery between the trials.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47439/1/424_2004_Article_BF00362956.pd

High-Pressure Amorphous Nitrogen

The phase diagram and stability limits of diatomic solid nitrogen have been explored in a wide pressure--temperature range by several optical spectroscopic techniques. A newly characterized narrow-gap semiconducting phase $\eta$ has been found to exist in a range of 80--270 GPa and 10--510 K. The vibrational and optical properties of the $\eta$ phase produced under these conditions indicate that it is largely amorphous and back transforms to a new molecular phase. The band gap of the $\eta$ phase is found to decrease with pressure indicating possible metallization by band overlap above 280 GPa.Comment: 5 pages, 4 figure

High temperature optical absorption investigation into the electronic transitions in sol–gel derived C12A7 thin films

Optical absorption into 6 mm thick sol–gel derived films, annealed at 1300 °C of 12CaO·7Al2O3 calcium aluminate binary compound on MgO〈100〉 single crystal substrates was studied at temperatures ranging from room temperature to 300 °C. Experimental data were analysed in both Tauc and Urbach regions. The optical band gap decreased from 4.088 eV at 25 °C to 4.051 eV at 300 °C, while Urbach energy increased from 0.191 eV at 25 °C to 0.257 eV at 300 °C. The relationship between the optical band gap and the Urbach energy at different temperatures showed an almost linear relationship from which the theoretical values of 4.156 and 0.065 eV were evaluated for the band gap energy and Urbach energy of a 12CaO·7Al2O3 crystal with zero structural disorder at 0 K