Semiconductor carrier lifetime

Band gaps of semiconductors carrier lifetimes shallow impurity or defect detection sample quality and structure... 

Radiative recombination of minority carriers is tlie most likely process in direct gap semiconductors. Since tlie carriers at tlie CB minimum and tlie VB maximum have tlie same momentum, very fast recombination can occur. The radiative recombination lifetimes in direct semiconductors are tlius very short, of tlie order of tlie ns. The presence of deep-level defects opens up a non-radiative recombination patli and furtlier shortens tlie carrier lifetime. 

The situation is very different in indirect gap materials where phonons must be involved to conserve momentum. Radiative recombination is inefficient, resulting in long lifetimes. The minority carrier lifetimes in Si reach many ms, again in tire absence of defects. It should be noted tliat long minority carrier lifetimes imply long diffusion lengtlis. Minority carrier lifetime can be used as a convenient quality benchmark of a semiconductor. 

Cartiers can also be generated in a semiconductor by the absorption of light or injected into the semiconductor from ap—n or Schottky junction. In either case, as soon as the source is removed the density of those excess carriers begins to decrease exponentially with time. The time it takes for the density to be reduced to 1/ of the original value is defined as the carrier lifetime, T. For siUcon, T is typically in the microsecond range. 

The PMC transient-potential diagrams and the equations derived for PMC transients clearly show that bending of an energy band significantly influences the charge carrier lifetime in semiconductor/electrolyte junctions and that an accurate interpretation of the kinetic meaning of such transients is only possible when the band bending is known and controlled. 

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... 

N. K. Dutta, Radiative Transitions 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, Elfects 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 equilibrium lever relation, np= n , can be regarded from a chemical kinetics perspective as the result of a balance between the generation and recombination of electrons and holes (21). In extrinsic semiconductors recombination is assisted by chemical defects, such as transition metals, which introduce new eneigy levels in the energy gap. The recombination rate in extrinsic semiconductors is limited by the lifetime of minority carriers which, according to the equilibrium lever relation, have much lower concentrations than majority carriers. Thus, for a >-type semiconductor where electrons are the minority carrier, the recombination rate is A /t. An = n — n0 is the increase of the electron concentration over its value in thermal equilibrium, nQy and Xn is the minority carrier lifetime. This assumes low level injection where An is much smaller than pQy the equilibrium majority carrier concentration. 

Chapter 1 focuses on the characteristics of deep states in wide band-gap III-V compound semiconductors, particularly the recombination properties which control minority-carrier lifetime and luminescence efficiency. These properties are significant for many optoelectronic devices, including lasers, LEDs, and solar cells. While this review emphasizes areas of extensive recent development, it also provides references to previous comprehensive reviews. The compilation of levels reported in GaAs and GaP since 1974 is an important contribution, as is the discussion of the methods used to characterize these levels. 

Hydrogenated amorphous silicon, a new form of a common element, is a semiconductor that has come of age. Its scientific attractions include a continuously adjustable band gap, a usable carrier lifetime and diffusion length, efficient optical transitions, and the capability of employing either n-or p-type dopants. 

The time-resolved microwave reflectivity (TRMR) techiuque is well established for contactless characterisation of minority-carrier lifetimes in semiconductors. It can be applied to map surface recombination in this case the sample is moved by an X-Y stage to allow spatially resolved measurement of the minority-carrier lifetime. 

Surface recombination of electrons and holes is also relatively slow. Usually, the recombination lifetime depends inversely on the majority carrier concentration at the surface. For a n-type semiconductor, the lifetime of a hole trapped at a surface state is given by r, = l/j w/, where is the rate constant for electron capture For example if n /A = 10 cm and the band-bending = ksT, nmrf =... 

It is highly probable that the metal contamination strongly affects the electrical properties of silicon carbide crystals and reduces the carrier lifetimes, as in other semiconductors. Unfortunately, no detailed studies of this effect have been reported thus far. 

Doped superlattices are proper for controllable semiconductor components. They are compatible with dense optical and electronic integration and could provide required performance characteristics of the devices. Unique features of the doped superlattices, or n-i-p-i crystals, are spatial separation of electrons and holes, tunable energy band gap, increased current carrier lifetime, wide variation of the potential profile and changing the electric and optical characteristics versus design parameters or added quantum wells and 6-doped layers [1,2],... 

Other Electrical Properties. A characteristic feature of many semiconductors and insulators is an increase in conductivity on absorption of light in a particular frequency range. This photoconductivity usually reflects an increase in the number of free carriers in the solid due to their photoexcitation from filled bands, donor levels, or trapping states. The spectral response and quantum eflSciency of the photoconductivity can be used to deduce information regarding the energy band structure of a semiconductor and the carrier lifetimes (or mobilities). 

So far only the recombination in the bulk and at the surface of the semiconductor are considered and the recombination in the space charge region is neglected. The assumption is valid only if the transit time of the photogenerated minority carriers across the depletion region is less than the minority carrier lifetime.151 167... 

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