C. Ogihara

Light-induced defect creation under pulsed subbandgap illumination in hydrogenated amorphous silicon

We have observed that pulsed subbandgap illumination creates dangling bonds with a density of about 10 18 cm m 3 in high-quality hydrogenated amorphous silicon films. Such a light-induced creation of dangling bonds can be accounted for in terms of a model in which self-trapping of holes in weak Si-Si bonds adjacent to a Si-H bond plays an important role. The kinetics of thermal annealing of the light-induced dangling bonds have been examined, in which half of the defects are annealed out at temperatures above 180C, but half of them remain.

Lifetime and intensity of photoluminescence after light induced creation of dangling bonds in a-Si:H

The photoluminescence (PL) fatigue after illumination of pulsed laser light has been studied for a-Si:H films prepared by glow discharge decomposition. The densities of photocreated dangling bonds (DBs) in the a-Si:H films after illumination of sub-bandgap pulsed light were obtained from electron spin resonance (ESR) measurements as a function of illumination time. We have obtained the lifetime resolved PL in microsecond and millisecond regions for a-Si:H films by means of frequency resolved spectroscopy (FRS) before and after the illumination. The decrease in the PL intensity was not so significant as expected from the DB density. We have not found sizable change of lifetime distribution of PL after the illumination. The results suggest inhomogeneity of spatial distribution of photocreated DBs.

Optical absorption of nanometer-sized band-edge-modulated amorphous silicon-nitrogen films

Abstract Optical absorption of nanometer-sized band-edge-modulated (BM) amorphous silicon–nitrogen (a-Si 1− x N x :H) films, BM films, are discussed using the effective medium expression and characterized in terms of the optical gap E g , the value of the slope in Tauc plot B, the Urbach energy E u and the refractive index n 0 as functions of the modulation period L and their correlations between them. E g in BM film increases with decreasing L without changing n 0 , i.e., average composition in the film. This results in the quantum-size effect. The values of B are hardly affected by L , while E u increases with decreasing L . The increase in E u is not expected from the effective medium expression and attributed to the effect caused by the sinusoidal modulation of the band-edge.

Light-induced Creation of Defects and Lifetime Distribution of Photoluminescence in a-Si:H Based Films

We have studied the lifetime distributions of photoluminescence (PL) at 10K after the pulsed excitation for a-Si:H based films. Effects of light-induced creation of defects on the lifetime distributions have been studied. The lifetime distributions of PL in a-Si:H based films have a distinct component at about 10 ns together with a longer lifetime component seen in microsecond region. The PL in a-Si:H decreases in intensity after the illumination of visible light. The decreasing of the nanosecond component is slower than that of microsecond component. The decreasing of the PL intensity and increasing of the defect density have also been observed in a-Si:H after illumination of sub-bandgap light, although the absorption coecient is much smaller than that of visible light. The quenching of PL is discussed with distribution of non-radiative lifetime calculated by assuming random distribution of the DBs.

Lifetime distribution of PL under pulsed excitation in hydrogenated amorphous silicon based films

Abstract Nanosecond processes of photoluminescence (PL) in a-Si:H based films have been studied using a tunable pulse laser illuminating samples at temperature of 10 K. The distribution of lifetimes of the PL has a component in the nanosecond region. The nanosecond component becomes largest in a-Si 1− x :N x :H alloys, a-Si:H/a-Si 1− x :N x :H multilayers and band-edge modulated a-Si 1− x :N x :H films. In the case of sub-bandgap excitation the nanosecond component is largest. The results are explained in terms of the singlet exciton model.

Amorphous Semiconductors: Structure, Optical, and Electrical Properties

This chapter is devoted to a survey of the structural, optical and electrical properties of amorphous semiconductors on the basis of their fundamental understanding. These properties are important for various types of applications using amorphous semiconductors.

Long-term metastability of light-induced defects in hydrogenated amorphous silicon

Abstract The decay of the peak intensity of the electron spin resonance signal associated with light-induced dangling bonds in a-Si(H) has been measured at room temperature as a function of time during very long intervals such as 3400 days after the intense pulsed illumination was turned off. The decay curve is fitted by an exponential function with a decay constant of 393 days and reaches a steady-state value smaller than the value taken before illumination. Such a long-term metastability of light-induced dangling bonds in a-Si:H is discussed in terms of reconstruction of the amorphous network occurring through hydrogen motion.

Measurements of defect PL in a-Si:H by means of frequency resolved spectroscopy

Defect PL in hydrogenated amorphous silicon (a-Si:H) has been studied by means of frequency resolved spectroscopy (FRS). The width of the lifetime distribution is represented by a value, obtained from the results of the FRS measurements in addition to the intensity and the characteristic lifetime. The results obtained for the a-Si:H films of various defect densities and their temperature variation are presented.

Excitons and Light Induced Creation Of Defects in Amorphous Silicon Based Films

Lifetime-resolved studies of photoluminescence (PL) after the light-induced creation of defects by illumination of pulsed light have been done for a-Si:H based films including a band-edge modulated (BM) a-Si 1 m; x N x :H film in which the PL is dominated by emission from excitons. The decrease in intensity of PL after the illumination of the BM film was more significant than that of a-Si:H. The role of excitons in the creation of light-induced defects is discussed.