The continuity equation of minority carriers is solved with the inclusion of photon recycling. A new development technique is used to provide a simple evaluation of effective lifetime and diffusion coefficients. Results are found to be in agreement with already published methods in a wide range of sample geometries. This provides a reliable determination method for radiative and nonradiative lifetimes through a single time-resolved photoluminescence experiment on GaAs structures such as solar cells.
In direct-gap semiconductors, self-absorption processes are known to increase minority carrier lifetimes. In this paper, an original method is developed to solve the dynamic continuity equation with the inclusion of self-absorption phenomena. Also named photo recycling, this process is treated in a model which takes into account the experimental conditions, together with geometrical and optical characteristics of the sample. This method is used to analyze photoluminescence decay experiments on angle-lapped GaAs/Ga0.15Al0.85As double heterostructures. The inclusion of the reabsorption effects is shown to improve the global fit of calculated luminescence with experimental data. This leads to a more accurate determination of key electronic parameters such as diffusion coefficient, surface recombination velocities, and nonradiative lifetime of minority carriers.
International audienceThe mechanical properties of interfaces and more precisely the adhesion are of great importance for the understanding of the reliability of thin film devices. Organic thin film transistors (OTFT) on flexible substrate are a new class of electronic components. Since these devices are flexible and intended for different fields of application like sensors and displays, they will undergo a lot of mechanical and thermal stress during their useful life. Moreover, interfaces play an important role in the electrical stability of these transistors. In this context, the adhesion of two organic submicron thin films, semi conducting and dielectric respectively, deposited on polymeric substrate were investigated by scratch test method. This study demonstrates the feasibility and selectivity of the scratch test as a tool for assessing the adhesion and the damage behaviour of ultra-thin organic film on flexible plastic substrate. The semi-crystalline substrate presents a brittle cracking damage from a given strain, whereas when covered by the semi-conducting thin film, the sample exhibits a more ductile behaviour. Moreover, this technique has proven to be sensitive enough to highlight the effects of a plasma treatment prior to deposition
International audienceMany adhesion test techniques have been developed to measure the adhesion energy of thin films but they are hard to implement in the case of submicron organic thin films deposited on a flexible substrate. Recently the feasibility and repeatability of the scratch test technique as a tool for testing the adhesion and the damage behaviour of ultra-thin films on polymer substrates has been demonstrated. However, direct comparison of the critical load between samples was not straightforward since different failure mechanisms were induced. In the present work, we have performed nanoscratch experiments on submicron thin films deposited on a flexible substrate. The use of a tip radius of 5 μm enabled a unique delamination mechanism to be induced by localizing and maximizing the stress closer to the interface. We have observed an increase of the critical load on samples processed with an adhesive plasma treatment prior to thin film deposition, confirming the effectiveness of this treatment. We have also performed mechanical ageing tests on specimens and proved that the scratch test technique is sensitive enough to monitor the degradation of the interface properties. Finally, we have discussed some existing energy models. Taking into account some limitations, Laugier's model gives an upper bound for the adhesion energy
Flexibility will significantly expand the application scope of electronics, particularly large-area electronics. Over the last ten years, printed organic electronic is believed to be one of the next major technological breakthroughs in the field of microelectronic and the use of printing technology to process organic fieldeffect transistors (OFETs) opens promising perspectives for low cost, large area circuits integrated on flexible, plastic substrates. With amorphous polymer-based thin films transistors acceptable electrical performances are now achieved with relatively good stability at ambient air. In literature a lot of work has been devoted to study degradation of device characteristics under bias stress conditions but only few papers deal with the mechanical behaviour. In this paper, we review our first reliability results obtained on flexible organic thin film transistors under mechanical stresses. The variations of electrical characteristics under bending tests, both in compression and tension, have been studied. Using specific equipment, we have also evaluated the reliability of transistors under cyclic bending tests. The stress dependency of the transfer characteristic deviates from the one observed for inorganic material like silicon.
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