Recombination generation rate

Equation (16.40), though rather complex in form, is of remarkable importance because it describes the overall charge transfer process via the valence band at a n-type semiconductor electrode for both anodic and cathodic polarizations. As mentioned earlier, jo represents the generation/recombination rate of holes in the bulk of the semiconductor and jo represents the rate of hole transfer at the interface. The ratio jo/ jy indicates whether the generation/recombination or the surface kinetics of the hole transfer is rate determining. If j0/yv° 1, i.e., the rate is controlled by surface kinetics due to slow hole injection, then... 

The widespread application of 10.6 pm heterodyne detection for communications, radar and infrared active imaging is presently restricted by the need to cool the detectors below temperatures obtainable from thermal electric coolers ( 180 K). Presently the main reason for cooling 10.6 pm heterodyne detectors is to reduce the thermal generation-recombination rate in the photoconductor or the diffusion current in diodes to a level that can be overridden by available laser local oscillator power. In general the use of photoconductors (with band gaps tailored for 10.6 pm radiation) seems to be a realistic approach to operation at 180 K or above. Since the thermal generation-recombination rate is of the order of 10 /t hole-electron pair per cm at 180 K it follows that a 1 pm thick, 10 cm area photoconductor with a carrier lifetime (t) of 10" s would require 1 milliwatt of LO power to approach hvB detector sensitivity at bandwidths of... 

Any intrinsic property that influences the conductivity of an electrodematerials system, or an external stimulus, can be studied by IS. The parameters derived from an IS spectrum fall generally into two categories (a) those pertinent only to the material itself, such as conductivity, dielectric constant, mobilities of charges, equilibrium concentrations of the charged species, and bulk generation-recombination rates and (b) those pertinent to an electrode-material interface, such as adsorption-reaction rate constants, capacitance of the interface region, and diffusion coefficient of neutral species in the electrode itself. 

There is a large number of bulk and surface mechanisms determining net generation-recombination rate in semiconductor devices. One of the usual approaches for taking them into account is to include surface recombination processes directly into the expressions for quantum efficiency, while bulk processes are calculated separately (e.g., [12, 13]). 

If excess concentrations are small enough compared to the equilibrium values, (1.83) transforms into a sum of separate and independent generation-recombination rates defined by minority carrier lifetimes for each separate fc-th mechanism [8]... 

In the same approximation, the reciprocal value of the resulting lifetime is given as a sum of reciprocal values of each separate mechanism (a ratio between the generation-recombination rate and the excess concentration of carriers). 

The total generation-recombination rate for narrow-bandgap direct semiconductors in the dark (i.e., without optical generation) is obtained as the sum of the rates for CCCH and CHHL Auger processes, radiative generation-recombination and single-level SR generation-recombination in the form... 

By introducing (3.17) into the divergence of (3.16) and simultaneously adding and subtracting net generation-recombination rate we obtain two continuity equations... 

The equihbtium lever relation, np = 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 energy levels in the energy gap. The recombination rate in extrinsic semiconductors is limited by the lifetime of minority carriers which, according to the equihbtium lever relation, have much lower concentrations than majority carriers. Thus, for a -type semiconductor where electrons are the minority carrier, the recombination rate is /S n/z. An = n — is the increase of the electron concentration over its value in thermal equihbtium, and... 

The recombination rate Ptlx, which is defined as the number of generated exci-tons in A/ divided by the number of generated excitons in At plus the number of minority carriers passing through the device in At, for an unbalanced LED (where j(x) jp(x) 3> j (x) and pp pH) is given by the following equation ... 

This means that the PMC signal will, apart from the generation rate of minority carriers and a proportionality constant, be determined by the interfacial charge transfer rate constant kr and the interfacial charge recombination rate sr... 

The conductivity K induced by radiation absorption at dose rate I (eV°=cm-3 s-1) is given by K = uc, where c the is free ion concentration and u is the sum of mobilities of positive and negative carriers. The establishment of steady state requires equal rates of generation and recombination, or IGR /100 = kc2 where k is the second-order recombination rate constant. Eliminating c between these... 

The half-life for the decomposition to yield HO is 1.9 s under physiological conditions. The recombination rate in the final reaction is slower than most other reactions involving HO, so that generation of hydroxyl radical in this fashion may be important physiologically [23]. 

The x-ray models used have been generated by a Hartree-Slater code [5,6] of J. Scofield s. Radiative recombination rates are calculated from the photoionization crossections. Information for the optical models has been drawn from a wide variety of sources. The ions included in the present calculation are Fel, n, HI, IV, V, VI Col, II, in, IV, V OI, n, HI, IV and Hel, H. Many important ions are not included, particularly in the intermediate Z range near Si. To minimize (but not eliminate) the effects of these... 

A drastically different behavior was found if the electrode was prepared by a mechanical cut normal to the van der Waals-sur-face. The dark current increases steeply above a critical anodic potential as is seen in curve 3 of Figure 5- Only a small photocurrent can be observed which quickly becomes indistinguishable from the dark current, if the electrode potential is further increased anodically. This shows that the recombination rate is much higher at this kind of surface and that electron injection into the conduction band is now catalyzed by surface states generated by the formation of steps and other surface imperfections (16). 

---