Investigation of Thermal Stability Effects of Thick Hydrogenated Amorphous Silicon Precursor Layers for Liquid Phase Crystallized Silicon

The thermal stability of thick amp; 8776;4 amp; 8201; amp; 956;m plasma grown hydrogenated amorphous silicon a Si H layers on glass upon application of a rather rapid annealing step is investigated. Such films are of interest as precursor layers for laser liquid phase crystallized silicon solar cells. However, at least half day annealing at T amp; 8776;550 amp; 8201; C is considered to be necessary so far to reduce the hydrogen H content and thus avoid blistering and peeling during the crystallization process due to H. By varying the deposition conditions of a Si H, layers of rather different thermal stability are fabricated. Changes in the surface morphology of these a Si H layers are investigated using scanning electron microscopy and profilometry measurements. Hydrogen effusion, secondary ion mass spectrometry SIMS depth profiling, and Raman spectroscopy measurements are also carried out. In summary, amorphous silicon precursor layers are fabricated that can be heated within 30 amp; 8201;min to a temperature of 550 amp; 8201; C without peeling and major surface morphological changes. Successful laser liquid phase crystallization of such material is demonstrated. The physical nature of a Si H material stability instability upon application of rapid heating is studie

Female Institutional Directors on Boards and Firm Value

The aim of this research is to examine what impact female institutional directors on boards have on corporate performance. Previous research shows that institutional female directors cannot be considered as a homogeneous group since they represent investors who may or may not maintain business relations with the companies on whose corporate boards they sit. Thus, it is not only the effect of female institutional directors as a whole on firm value that has been analysed, but also the impact of pressure-resistant female directors, who represent institutional investors (investment, pension and mutual funds) that only invest in the company, and do not maintain a business relation with the firm. We hypothesize that there is a non-linear association, specifically quadratic, between institutional and pressure-resistant female directors on boards and corporate performance. Our results report that female institutional directors on boards enhance corporate performance, but when they reach a certain threshold on boards (11.72 %), firm value decreases. In line with female institutional directors, pressure-resistant female directors on boards also increase firm value, but only up to a certain figure (12.71 % on boards), above which they have a negative impact on firm performance. These findings are consistent with an inverted U-shaped relationship between female institutional directors and pressure-resistant female directors and firm performance

Raman spectroscopic analysis of the effect of annealing on hydrogen concentration and microstructure of thick hot wire grown a-Si:H films aimed as precursor layers for crystallized thin film silicon

For application as precursor layers for silicon solar cells fabricated by laser liquid phase crystallization, thick amorphous silicon films on glass are of interest. However, for hydrogenated amorphous silicon (a-Si:H) precursor layers containing about 10 at.% hydrogen, hydrogen needs to be removed prior to liquid phase crystallization to avoid bubble formation and peeling. For this purpose, an at least 12 hours annealing procedure up to 550°C is considered necessary thus involving long process time and high costs. In this article, we investigate the use of thick hot wire grown a-Si:H films which turn out to need considerably less time for dehydrogenation than dense plasma-grown a-Si:H. The dehydrogenation process is studied by depth profiles of hydrogen concentration and medium range order (MRO) using Raman spectroscopy analysis at etch pits. The results show already at an annealing temperature of 450°C the disappearance of all detectable H in the substrate-near part and the complete removal of H at 550°C after about 4 hours annealing. We attribute this rather fast hydrogen removal to the formation of interconnected voids primarily in the substrate-near range. In the same range of the film, we find a correlation between hydrogen concentration and medium range order suggesting that a silicon network reconstruction due to hydrogen out-diffusion causes an observed decrease of reciprocal MRO. The results stress the importance of void-related microstructure in the a-Si:H for hydrogen removal at a rather low annealing temperature and short annealing time. Our results suggest that hot wire a-Si:H films which can be grown with a high deposition rate and a rather pronounced void-related microstructure may be well suited as economic precursor layers

Absorption Coefficient of a Semiconductor Thin Film from Photoluminescence

The photoluminescence (PL) of semiconductors can be used to determine their absorption coefficient (a) using Planck's generalized law. The standard method, suitable only for self-supported thick samples, like wafers, is extended to multilayer thin films by means of the transfer-matrix method to include the effect of the substrate and optional front layers. a values measured on various thin-film solar-cell absorbers by both PL and photothermal deflection spectroscopy (PDS) show good agreement. PL measurements are extremely sensitive to the semiconductor absorption and allow us to advantageously circumvent parasitic absorption from the substrate; thus, a can be accurately determined down to very low values, allowing us to investigate deep band tails with a higher dynamic range than in any other method, including spectrophotometry and PDS