D. Wagner

Ar+ laser induced chemical vapor deposition of Si from SiH4

For the first time polycrystalline silicon has been grown by using the visible light of an Ar+ laser for pyrolytical decomposition of SiH4. With a laser irradiance of 3600 W/mm2 a deposition rate of 30 μm/s was obtained. The temperature dependence of the deposition rate was investigated. The kinetically controlled regime is characterized by an activation energy of 44±4 kcal/mole.

Laser grown single crystals of silicon

Single crystal rods of silicon have been grown by laser-induced chemical vapor deposition (LCVD) using visible light. We believe these to be the first reported single crystals of any material grown by LCVD.

On the application of the Meyer-Neldel rule to a-Si:H

The dependence of the conductivity prefactor sigma 0 on the activation energy Ea in a-Si:H has been determined by measuring the Staebler-Wronski effect (1977, 1980) in undoped and n-doped glow discharge a-Si:H samples and by comparing DC conductivity measurements in differently n-doped samples in defined states. A very exact linear dependence of ln sigma 0 on Ea as described by the Meyer-Neldel rule is observed, with good quantitative agreement between the parameters for the two cases. On the basis of these results it is proposed that the Meyer-Neldel rule is fundamental in a-Si:H, by which it is meant that it has to be taken into account in any model for the electronic transport properties of this material, and that it should not be explained by a model specific to a-Si:H.

Soft modes in semiconducting SrTiO3: II. The ferroelectric mode

The frequency, temperature and wavevector dependence of the ferroelectric soft mode in semiconducting SrTiO3 was investigated by temperature derivative Raman spectroscopy and by inelastic neutron scattering. A tremendous shift in mode frequency with “free” electron and oxygen vacancy concentration, respectively, was observed.

The Staebler-Wronski effect and the Meyer-Neldel rule in amorphous silicon

Abstract Good agreement between the Meyer-Neldel behaviour for the Staebler-Wronski effect (SWE) and for doping is shown by DC dark conductivity measurements in a-Si:H. This indicates the general character of the Meyer-Neldel rule in this material and leads to considerations showing the bulk nature of the SWE. Its possible origin from internal band bending is suggested by its dependence on preparation conditions.

Photoconductivity measurements in a-Si:H by frequency-resolved spectroscopy

The first experimental results of photoconductivity measurements in a-Si:H using in-phase and quadrature frequency-resolved spectroscopy (FRS) are reported. The main feature of the response curves of quadrature FRS is a double peak structure. The relative intensities of the peaks are strongly dependent on external parameters such as temperature and generation rate and on the Staebler-Wronski state, indicating the existence of two recombination mechanisms with different characteristic times.

On the annealing behaviour of the Staebler-Wronski effect ina-Si:H

The kinetics of the Staebler-Wronski effect ina-Si:H were investigated experimentally. The rate of recovery from the illuminated state B to the annealed state A was observed at various temperatures in undoped,n- andp-dopeda-Si:H. The data can be characterized by a thermally activated relaxation time with an activation energy decreasing with increasing doping concentration. The results are compared with previous data and existing models.

A polarizability model for the ferroelectric mode in semiconducting SrTiO3

The temperature dependence of the ferroelectric mode frequency in SrTiO3 with oxygen vacancies and free electrons, is quantitatively explained on the basis of a microscopic model for ferroelectric soft modes.

The role of surface layers in dielectric measurements in oxidic perovskites

From anomalies in impedance data of SrTiO3 and BaTiO3 the existence of a surface layer can be concluded. The implications of such a layer on the interpretation of dielectric data in general are discussed.

The influence of contact effects on the dielectric behaviour of diffuse phase transitions

Abstract The importance of contact effects for the interpretation of the dielectric response of diffuse phase transitions is proved on single crystal PMN. The measured dielectric properties are shown to depend on electrode material and on sample thickness.