Diffusion length, lifetime

Obtaining information on a material s electronic band structure (related to the fundamental band gap) and analysis of luminescence centers Measurements of the dopant concentration and of the minority carrier diffusion length and lifetime... 

The diffusion length can thus be calculated since a is typically known, or since =(t D)1/2, the bulk lifetime provided the diffusion coefficient... 

Self-doped polymers, 334 Semicircles, Albery and Mount interpretation of, 584 Semiconductor electrodes with polymer layers, 499 diffusion length in, 492 Semiconductors, lifetime for carriers and, 495... 

In the presence of an electric field the drift length is the mobility-lifetime product times the electric field A.mfp = prE [576]. With typical values of pz and E the mean free path usually exceeds by far the thickness of the solar cell, and virtually all photogenerated carriers can be collected. However, under certain operating conditions, field-free regions in the / -layer may exist, and the collection efficiency is decreased because the diffusion lengths of the carriers are much smaller than the thickness of the solar cell [11, 577]. 

The three summands found in the right-hand side of expression (5.10) correspond to the three major channels (ways) of EEP losses the first summand characterizes the gaseous-phase de-excitation due to collisions, the second one stands for the gaseous-phase de-excitation on account of spontaneous radiation, and the third summand characterizes the heterogeneous decay of EEPs. A possible contribution of the radiative term to the value of ) D can be done a priori. With the radiative time of EEP lifetime r,ad known from the spectroscopy, one can easily estimate (by the formula of Einstein) the diffusion length over which the radiative decay of EEP will be perceptible ... 

Contamination of silicon wafers by heavy metals is a major cause of low yields in the manufacture of electronic devices. Concentrations in the order of 1011 cm-3 [Ha2] are sufficient to affect the device performance, because impurity atoms constitute recombination centers for minority carriers and thereby reduce their lifetime [Scl7]. In addition, precipitates caused by contaminants may affect gate oxide quality. Note that a contamination of 1011 cnT3 corresponds to a pinhead of iron (1 mm3) dissolved in a swimming pool of silicon (850 m3). Such minute contamination levels are far below the detection limit of the standard analytical techniques used in chemistry. The best way to detect such traces of contaminants is to measure the induced change in electronic properties itself, such as the oxide defect density or the minority carrier lifetime, respectively diffusion length. 

The method described so far measures diffusion length but provides no information about the element responsible for the contamination. This information can for some cases be obtained indirectly, if the change in lifetime with temperature or injection level is measured. Injection levels in the FPC mode are generally one or two orders of magnitude smaller compared to the BPC mode at the same... 

The space charge region is denoted by length w, while Lp is the hole (minority carrier) diffusion length. Zp is the minority carrier (hole) lifetime, jp the (minority carrier) hole mobility, and Dp the minority carrier diffusion coefficient. 

A high gain transistor requires a nearly equal to 1. In the absence of collector junction breakdown, a is the product of the base transport factor and emitter efficiency. The base transport factor, aT, is the fraction of the minority current (electrons for an n-p—n transistor) that reaches the collector. ocT 1 — W2 /2L, where W is the base width, is the distance between emitter and collector junctions and Lg is the minority carrier diffusion length in the base. High gain transistors require a thin base as well as a long minority carrier lifetime for a large Lg. Because aT is >0.995 in modem transistors, there is little room for improvement. The emitter efficiency, the fraction of emitter current due to minority carriers injected into the base instead of the emitter,... 

Other indirect methods for measuring lifetimes often involve device structures such as p-n junctions. The electron-beam-induced current (EBIC) technique, for example, measures the increase injunction current as an impinging electron beam moves close to the junction, i.e., within a few minority-carrier diffusion lengths. If a diffusion constant can be estimated, say by knowledge of the minority-carrier mobility, then the minority-carrier lifetime can be calculated. However, SI GaAs does not form good junctions, so such methods are really not applicable. 

Here Dp is the hole diffusion coefficient and Lp = (Dptp)112 is the diffusion length, where tp is the hole lifetime. This expression for ijjm coincides with a known formula (see, for instance, Middlebroock, 1957) for the saturation current of a p- junction. 

Direct determination of the rate of the C- or Y-Dye formation reaction in the individual microdroplets has been made possible by potential application of the laser trapping-spectroscopy-electrochemistry technique. Furthermore, the dye formation reaction efficiency in each droplet could be controlled arbitrarily by the distance between the droplet and the electrode. Under the present experimental conditions (i.e., pH 10 and [SO] ] =20mM), the diffusion length of QDI within its lifetime is only several micrometers, so the distance dependence of the reaction is unique in the micrometer dimension. The present approach will therefore lead to a new methodology to control chemical reaction in micrometer-size volumes. 

The lifetime T and diffusion coefficient D of photoinjected electrons in DSC measured over five orders of magnitude of illumination intensity using IMVS and IMPS.56) fis proportional to the r m, indicating that the back reaction of electrons with I3 tnay be second order in electron density. On the other hand, D varied with C0 68, attributed to an exponential trap density distribution of the form Nt(E) <=< exp[ P(E - Ec)l(kBT) with 0.6. Since T and D vary with intensity in opposite senses, the calculated electron diffusion length L = (JD-z)m does not change linearly with the irradiance. 

In the above, L is the hole diffusion length, t is the lifetime, p0 is the equilibrium hole density, and is the equilibrium band bending voltage. These equations are good approximations when 5 is not too small and are equivalent to that given in (2J where the exchange current parameter is used instead of the charge transfer rate constant. More accurate... 

As a result of light trapping and intercalation, thin film solar cells can be made of a thickness /, which apparently violate the condition Le,h l 1 /a. Even with light trapping, the thickness l must be of the order of the penetration depth /a of the light. The diffusion length, on the other hand, can be arbitrarily small, if caused by a small diffusion coefficient. The recombination lifetime should always be as large as possible and should approach the radiative lifetime. 

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