Changes In Dark Conductivity Research Articles

Light-induced metastable effects in hydrogenated amorphous silicon

This paper reviews various light-induced metastable effects in a a-Si: H : changes in dark conductivity (Staebler-Wronski effect), increased spin resonance signal due to dangling bonds, reduced luminescence efficiency, emergence of emission at ≈0.8 eV , and also field-induced observations. The defects can be produced not only by irradiation with visible light, but also by X-rays, electron or ion bombardment, and even by ambipolar injection.

Characterized of glow-discharge deposited a-Si:H

The study of hydrogenated amorphous silicon, a-Si:H has become an active and large subfield of growing interest in noncrystalline semiconductors. This paper reviews recent successes as well as difficulties encountered in interpreting some fundamental physical properties of a-Si:H prepared by glow-discharge deposition. This material appears to contain structural and compositional heterogeneities which depend on the preparation conditions and affect its mechanical and electronic properties. These are related to the concentration and bonding configurations of hydrogen. Determinations of the density and distribution of localized gap states by means of field effect and capacitance measurements are discussed as well as evidence for and against the presence of surface states. Optical absorption near the absorption edge is described as are conductivity measurements. The latter reveal many interesting puzzles. Staebler and Wronski discovered that the dark conductivity and the photoconductivity can be changed significantly by strong exposure to light. Moreover, space charge layers adjacent to the substrate interface and near the free surface can strongly influence the electronic properties of a-Si:H films, especially those having low densities of gap states. The pre-exponential factor of the conductivity increases with its activation energy in accordance with the Meyer-Neldel rule regardless of whether the changes in dark conductivity are produced by doping, light exposure or space charge layers. Attempts are made to identify causes for the scatter of data on some film properties reported by various laboratories. Our present understanding of the recombination processes involved in photoluminescence and photoconductivity is presented. We conclude that a-Si:H films of superior quality can be expected when the preparation conditions become more fully understood.

高周波スパッタ法による水素化非晶質シリコン（ａ‐Ｓｉ：Ｈ）へのＩＩＩ族元素添加効果

Doping effects of group III elements to hydrogenated amorphous silicon (a-Si : H) have been investigated using co-sputtering of poly-crystalline Si and dopant elements. Compared with gaseous doping of boron by glow discharge (GD) method, doping efficiency of Al and Ga by RF sputtering is smaller at lower doping concentrations (less than 0.5%), but at higher concentrations dark conductivity changes drastically more than 10 orders of magnitude, and high dark conductivity (10-1 ohm-1 cm-1) with low activation energy (0.02 eV) can be achieved. Optical band gap decreases with increasing doping concentration.