Time-of-flight experiment

Time-of-flight experiments are used to measure particle velocities and particle mass per charge. The typical experiment... 

Lifetime measurements have elements in eommon with both eounting and time-of-flight experiments [4, 5]. In a lifetime experiment there is an initiating event that produees the system tliat subsequently deeays witli the emission of radiation, partieles or both. Deeay is statistieal in eharaeter taking as an example luielear deeay. 

T. Tiedje, Information about Band-Tail States from Time-of-Flight Experiments Arnold R. Moore, Diffusion Length in Undoped a-Si H W. Beyer and J. Overhof, Doping Effects in a-Si H H. Fritzche, Electronic Properties of Surfaces in a-Si H CR. Wronski, The Staebler-Wronski Effect... 

Experimentally, the charge mobilities are obtained by time-of-hight-measure-ments or by characterizing held-effect-transistor devices made of the materials. In time-of flight experiments, the mobility p is directly given by... 

T. Tiedje, Information about band-Tail States from Time-of-Flight Experiments... 

Time-of-Flight Experiments in Amorphous Chalcogenide Semiconductors... 

Charge transport through organic polymeric systems shows some unusual features. When the time of flight experiments are performed in inorganic crystalline solids the charge carriers drift in a sheet without any dispersion (except for the normal diffusion effects). All the carriers exit the sample at a specific time Tt. However a similar experiment with polymer films shows a very dispersive transit (Fig. 5 a) which indicates that only a small fraction of the carriers exit the sample at t = Tt. 

Time-of-flight measurements — In the context of an electrochemical measurement a time-of-flight experiment is designed to measure the diffusion coefficient of... 

Time-of-flight experiments have been used for over three decades to characterize carrier mobilities in crystal, and polycrystalline and disordered organic solids including molecularly doped polymers and molecular glasses [28,424,430,431]. Relatively high values (up to several hundreds cm2/V s) and hot carrier effects have been observed in... 

PDAs A Model of CPs Without Disorder In PDAs one would expect to have only two processes to consider transport along a really periodic chain, and all similar interchain hopping events. The case of PDAs illustrates the ambiguities of transport studies on CPs. Early time-of-flight experiments yielded mobilities ==5 cm2/V s along the chains, and 10 3 along the perpendicular directions [217]. A mobility of a few cm2/V s is typical of a molecular crystal, and the polymer character was not apparent. 

The drift mobility has the expected power law decrease with time. To obtain Pu from the transit time in the time-of-flight experiment, the transit time is defined, somewhat arbitrarily, as the time when the average carrier is half way across the sample. 

Returning to the expressions for the mobility given by Eqs. (3.18) and (3.20), it must be stressed that the thickness and field dependences are artifacts of the time-of-flight experiment and are not intrinsic properties of the mobility, which is only time-dependent. The artifact arises because the transit time changes with the sample thickness or applied field and the measurement of the mobility Hu(0 then applies to a different time. It is also of note that the measured mobility in Fig. 3.13... 

Fig. 3.15 illustrates the point, and shows the mobility as a function of temperature according to Eq. (3.18) for constant measurement time. The actual mobility in a time-of-flight experiment is measured at constant drift length (the sample thickness) and is indicated by the dashed intersecting line, because the time of the experiment increases... 

There are several techniques for measuring the mobility in a-Si H, most notably the time-of-flight method. All the techniques measure the average motion of the carriers over a time longer than that taken to trap a carrier in the band tail states, so that the drift mobility is always measured, rather than the free carrier mobility. The drift mobility depends on the distribution of traps and the free mobility can only be extracted if the density of states distribution is known. Chapter 3 describes how the time-of-flight experiment is used to determine the shape of the band tail through the analysis of the dispersive transport process. 

The value of UpT is obtained from the time-of-flight experiment which measures charge transported by the drift of optically excited carriers across a sample (see Section 3.2.1). Deep trapping causes the... 

Time-of-flight experiments find that in undoped a-Si H, is about seven times larger than 1]> Xe, indicating that electron transport dominates. The values of (IqX are not necessarily the same in photoconductivity, but there is general agreement that electrons contribute most. 

Bos and Burland (1987) measured hole mobilities of PVK with very low hole concentrations. The concentrations were of the order of 10-2 those normally used for time-of-flight experiments. The transit times were found to... 

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