Effective carrier lifetimes

In the above derivation we have implicitly assumed that x represents the effective carrier lifetime including the possiblity of lifetime reduction by sweepout. The theory of minority carrier sweepout is not yet rigorous, so that this assumption may be questionable. 

The second term in this expression increases in proportion to the optical power, resulting in a consequent reduction in the effective carrier lifetime. In practical devices, injected optical power on the order of 10 mW may result in reduction of the carrier lifetime to an effective value of 100 ps or less. 

Equation (4.58) represents the minority carrier sweepout effect. The total concentration Ap of photoexcited holes maintained in the photoconductor by steady-state irradiation is lower the stronger the electric field, because the field sweeps out some of the holes. The quantity T f(z) in (4.58) can be thought of as an effective carrier lifetime, reduced from the bulk lifetime by the sweepout effect. 

The contribution by the generation-recombination current to the overall current is negligibly small for ZnO even for very small effective carrier lifetimes, because the intrinsic carrier concentration is nearly zero at room temperature (RT). Even at... 

If tlie level(s) associated witli tlie defect are deep, tliey become electron-hole recombination centres. The result is a (sometimes dramatic) reduction in carrier lifetimes. Such an effect is often associated witli tlie presence of transition metal impurities or certain extended defects in tlie material. For example, substitutional Au is used to make fast switches in Si. Many point defects have deep levels in tlie gap, such as vacancies or transition metals. In addition, complexes, precipitates and extended defects are often associated witli recombination centres. The presence of grain boundaries, dislocation tangles and metallic precipitates in poly-Si photovoltaic devices are major factors which reduce tlieir efficiency. 

The variations in D and D and the much larger value for In show the limitations of a simple hydrogen atom model. Other elements, particularly transition metals, tend to introduce several deep levels in the energy gap. For example, gold introduces a donor level 0.54 eV below D and an acceptor level 0.35 eV above D in siHcon. Because such impurities are effective aids to the recombination of electrons and holes, they limit carrier lifetime. 

Silicon wafer has been extensively used in the semiconductor industry. CMP of silicon is one of the key technologies to obtain a smooth, defect-free, and high reflecting silicon surfaces in microelectronic device patterning. Silicon surface qualities have a direct effect on physical properties, such as breakdown point, interface state, and minority carrier lifetime, etc. Cook et al. [54] considered the chemical processes involved in the polishing of glass and extended it to the polishing of silicon wafer. They presented the chemical process which occurs by the interaction of the silicon layer and the... 

Ion implantation generates many dangling bonds that form centers for nonradiative recombination. These centers decrease the carrier lifetime and compete effectively with radiative transitions. However, after hydrogenation, since hydrogen ties dangling bonds, the luminescence process becomes more efficient. Furthermore, since the 1.0-eV emission is obtained even before hydrogen is introduced, the new radiative center may be formed due to residual hydrogen in the c-Si that combines with the implantation-induced defects. 

For a comparison of different photoconductors, a knowledge of their photoelectric gains is very important. However, it should not be forgotten that G depends, among other factors, on the mean lifetime r. Since the parameters responsible for the mean carrier lifetime depend considerably on structural effects... 

Fig. 5. Energy above the valence band of levels reported in the literature for GaP. Arrangement and notations are the same as in Fig. 4. Abbreviations for experimental methods not defined in Fig. 4. are temperature dependence of resistivity (RT), temperature dependence of minority-carrier lifetime (LT), Hall effect (H), and photostimulated electron paramagnetic resonance (PEPR).

N. K. Dutta, Radiative Transition in GaAs and Other III-V Compounds R. K. Ahrenkiel, Minority-Carrier Lifetime in III-V Semiconductors T. Furuta, High Field Minority Electron Transport in p-GaAs M. S. Lundstrom, Minority-Carrier Transport in III-V Semiconductors R. A. Abram, Effects of Heavy Doping and High Excitation on the Band Structure of GaAs D. Yevick and W. Bardyszewski, An Introduction to Non-Equilibrium Many-Body Analyses of Optical Processes in III-V Semiconductors... 

The rate constants for electron transfer and recombination are readily separated because in the limit (w- 0), equation (8.31) tends to kir/(ktr + krec), and the maximum of the semicircle occurs when ca = 2ir f=kt + krec. In the absence of RC attenuation effects, the high frequency intercept of the IMPS plot (minority carriers. Measurements of gac as a function of potential (band bending) can be used to determine the minority carrier lifetime and absorption coefficient [46]. The main advantage of using the IMPS data rather than dc measurements of... 

Warman JM, de Haas MP, Anthopoulos TD, de Leeuw DM. (2006) The negative effect of high-temperature annealing on charge-carrier lifetimes in microcrystalline PCBM. Adv Mater 18 2294-2298. 

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