Carriers transit time

Two main methods have been used to measure the charge carrier mobility in electroluminescent polymers time of flight (TOF) carrier transit time measurements and analysis of the current-voltage (1-V) characteristics of single carrier devices in the space charge-limited current (SCLC) regime. A summary of the results for the hole mobility of PPV and PPV-related polymers is given in Table 11-1 [24, 27-32]. For... 

Tyworth JE, Zeng AZ (1998) Estimating the effects of carrier transit-time performance on logistics cost and service. Transportation Research Part A Policy and Practice 32 (2) 89-97... 

Under realistic experimental conditions, additional dispersion may well be introduced as a consequence of factors, such as a finite initial width of excess carrier packet or fluctuations in electric field across a specimen film. Most, if not all, of these factors would be expected to yield a relative dispersion that decreases with increasing specimen thickness. In a well-conducted experimental measurement, a relative dispersion of the order of 20% might typically be achieved, giving a transit pulse similar to that shown in Fig. 3.2 (full line) (from which the mean carrier transit time is readily determined). 

The preceding characterization of anomalously dispersive transit pulses aroused considerable interest, both from a theoretical and an experimental viewpoint. Attention focused on the latter was stimulated by the possibility of using the log-log display technique to identify ft in cases where the dispersion was such as to obscure any change of gradient in conventionally displayed transit pulses. However, it became necessary to question the validity of such measurements of ft under conditions where individual carrier transit times vary over such a wide range. 

The function given by dj(t)/dt (calculated case) has a maximum that can be identified as the carrier transit time, which can be derived by using Newton s method of finding the root for the maximum of corresponding equation (for details see Ref. [11]). 

In EP-A-0007669 ion-etching is used to provide meandering current path in the active area. This increases the current path and the charge-carrier transit time thereby improving the responsivity. 

Here, tt = d//xF is the carrier transit time dependent on the carrier mobility, n, and electric field, F, operating in the sample. The bimolecular decay of holes and electrons can be expressed by the recombination time... 

To get a better physical picture of the phenomena underlying PR, it is convenient to replace the rate constants by their inverses Trec = k, and xt = k x which have been defined as the recombination time (292) and carrier transit time (248), respectively. Then,... 

SCLC given by Equation (8.50). The analysis of Many and Rakavy (1962) shows that the peak current is approximately 1.2 times the SCLC and that the maximum occurs at approximately 0.8 times the carrier transit time. Goldie (1999) has incorporated the experimentally observed Poole-Frenkel field dependence into this model and finds a range of possible numerical factors for the current maximum of from 1-1.2 times the SCLC and 0.7-0.8 times the transit time. Experimental data come close to these model profiles, see Abkowitz et al. (1994), Goldie (1999). 

A typical nondispersive TOP transient signal, x is the transit time of the leading front carrier, and 1/2 is the average carrier transit time. 

Additionally, AS can be used to delineate carrier mobilities in organic electronic materials. By solving the drift current equation and the Poisson equation for 4c/ one can show analytically that the admittance Y(o)) depends on the carrier transit time. Furthermore, the differential susceptance, AB=(o(C-Co), which is a measure of the differential capacitance, exhibits a peak in a plot of -AB vs/ The characteristic time =1// (at/., the maximum in -AB appears) is related to the average transit time t,/2 of the carriers via Equation 3.20. Hence, by measuring/ in a -AB vs/(Figure 3.7b), one can deduce x /2 and the carrier mobility from the following relation ... 

When designing a high-speed photodiode, one has to consider a number of tradeoffs. These tradeoffs can be related to the intrinsic layer thickness W, as T, carrier transit time, and the RC circuit time constant all depend on W. For conventional top- or back-iUuminated photodiodes, on the one hand, W needs to be thin to reduce the transit time. By doing so, on the other hand, -q and the RC time constant are compromised. To reduce the RC time effect, the detection area needs to be reduced, and this further reduces q, as illustrated in Fig. 9.73 (Bowers and Burrus, 1987). 

The second term to optimize within the D f product is the response time. This factor is very complex and in a photonic detector it is determined, among others, by the time of carrier diffusion to the depletion region, the time of transit across the active region, the carrier sweepout time (in photoconductors), the detector RC constant, and by the RC constant of external circuitry [7]. The response time is fundamentally limited by the carrier transit time [8], and this time is inversely proportional to the thickness of the active region. 

The amplification of the radiation at the resonant wavelength in an RCE device and rejection of others results in a increased spectral selectivity of resonant detectors. A logical consequence is an increase of the detector speed [275] which becomes limited by carrier transit time. Another consequence is an increase of the allowed operating temperature because of the shift of the BLIP limit [276]. The high spectral selectivity of RCE detectors may prove advantageous or disadvantageous, depending on the concrete application. 

Boltzman constant carrier mobility carrier transit time Conduction band Copper phthalocyanine Current... 

An appearance of such a minimum in the C/Co versus frequency plot allows the determination of the charge carrier mobility. From the drift current equation and the Poisson equation for Jao one can deduce that the admittance Y co) depends on the carrier transit time. Then, because also the differential susceptance AB, which is related to the differential capacitance... 

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