Electronic characterisation and computer modelling of thin film materials and devices for optoelectronic applications

lock-in techniques. A comparison was made of the two-beam photogating experiment, with a single beam current-voltage measurement, which is also influenced by trapped space charge, as indicators of defect distributions. It was found that the photogating measurement is a more accurate indicator of the distribution of space charge, and hence defects, within a device. Application of the photogating effect in a colour detector is introduced and detector structure proposed. The simple structure and the thin film technique of a-Si:H deposition suggests the possibility of a low cost photodetector with high colour resolution. Double beam collection efficiency measurements have been carried out on hydrogenated amorphous silicon p-i-n devices. Apparent collection efficiencies higher than unity were observed, and explained by a process identified as photogating, in which a low intensity weakly absorbed probe beam modulates the photocurrent produced by a high intensity strongly absorbed bias beam. Computer simulations were used to gain insight into the photogating phenomenon. It was found that the gating effect operates by the modulation of the internal field profile in a device, via deeply trapped space charge introduced by the probe beam. Conditions for high collection efficiencies were identified by modelling and by experiment. Collection efficiencies of 100 or greater could be achieved, much higher than any previously reported in the literature. The effects of external parameters including bias and probe beam wavelength and intensity, and applied voltage were studied. Additionally, the effects of internal parameters, such as the density and spatial distribution of defects, were investigated. The photogating phenomenon proved a sensitive and potentially useful indicator of defect density. The time response of the photogating effect revealed slow components to the response, associated with the need to involve deeply trapped space charge in the effect. Measurements of this time response explain in part the much lower values of collection efficiency reported earlier, which were made using a

Holistic approach of lean thinking in learning factories

Simulation games that employ the "learning by doing" approach are used to transfer complex knowledge from the most diverse fields of economy. Their popularity steadily continues to grow in the framework of seminars and workshops. The Institute of Production Systems and Logistics (IFA) applies this style of haptic learning in order to teach Lean Management contents to students as well as industry specialists and executives. During the interactive training sessions participants are involved in realistic operating situations including actual assembly processes and learn practically relevant research contents. This paper presents a training concept offered within the "IFA Lernfabrik" that incorporates the philosophy and application of Lean Thinking. Particular attention is given to the simultaneous consideration of production and administration. This synchronized approach is based on the fact that presently the administration side offers very high productivity potentials, while the vast majority of improvement activities is performed in production. To provide a better understanding for this approach, an interactive two-stage training environment was designed to highlight the advantages of Lean Production and Lean Administration methods. The first stage challenges the participants with a situation that is characterized by an inefficient production environment and limited administrative features. The aim is to improve the current situation through the utilization of the lean methods learned during the first stage training session. Within the second stage, the administrative features are being extended, which initially still exhibit wasteful characteristics. It becomes obvious that the advantages of an optimized production are not fully realized due to inefficient administrative processes. This clarifies the principle that productivity improvement activities should always entail an integral optimization of business processes. Therefore, the participants subsequently learn how to transfer and apply the methods of Lean Production in administration as tools to not only optimize their production but the entire organizational structure

Fundamental Phenomena and Applications of Swift Heavy Ion Irradiations

Peer reviewe

Collection efficiencies greater than unity by electron or hole gating in a-Si:H p-i-n diodes

AbstractWe report measured electron and hole gating in thick a-Si:H (3.5 μm) p-i-n diodes under reverse bias conditions. Previous publications have shown very high collection efficiency values for electron gating (p-side bias, n-side probe) of up to 50 (i.e. 5000%) for measured and simulated data and predictions of up to 400 (i.e. 40000%) from simulations. Reversing the usual sides of illumination for (electron) gating a situation can be created where, by n-side bias and p-side probe illumination, holes can be gated to travel through the sample to be collected at the contact. Even though the holes have much lower mobility, by this process we can still obtain collection efficiencies greater than unity. This measurement is more difficult because of unwanted illumination by stray bias beam photons on the more sensitive p-side, caused by reflections within the apparatus. Simulation of this situation corroborates qualitatively the measured data. A wide ranging study of the gating phenomenon in relation to different incident wavelengths and photon fluxes for bias and probe beam is reported. We present comparisons of electron and hole gating by measurement and simulation and explain the phenomenon for both electron and hole gating in terms of field changes near to the incident bias interface.</jats:p