Growth rate kinetic regime

Growth rate in the mononucleation regime Growth rate in regime I, II, III, respectively Substrate length Persistence length Kinetic length... 

In the A sector (lower right), the deposition is controlled by surface-reaction kinetics as the rate-limiting step. In the B sector (upper left), the deposition is controlled by the mass-transport process and the growth rate is related linearly to the partial pressure of the silicon reactant in the carrier gas. Transition from one rate-control regime to the other is not sharp, but involves a transition zone where both are significant. The presence of a maximum in the curves in Area B would indicate the onset of gas-phase precipitation, where the substrate has become starved and the deposition rate decreased. 

Initially, when the ApBq layer is very thin, the reactivity of the A surface is realised to the full extent because the supply of the B atoms is almost instantaneous due to the negligibly short diffusion path. In such a case, the condition kom kW]/x is satisfied. Therefore, if the surface area of contact of reacting phases A and ApBq remains constant, chemical reaction (1.1) takes place at an almost constant rate. In practice, this regime of layer growth is usually referred to as reaction controlled. The terms interface controlled regime and kinetic regime are also used, though less suited. 

LP-CVD ZnO In contrast to AP-CVD processes, LP-CVD processes are kinetically limited, i.e., the growth rate of the film depends mainly on the rate of reactions at the growing surface. These reactions become the limiting factor, because the transport time necessary to carry the reactant from the gas inlet to the growing surface is strongly reduced by choosing the low pressure regime. 

It does depend on the concentration of the reactive gases and of the coefficient of surface kinetics ks. As often, the activation of the chemical reactions follows an Arrhenius law and ks is expressed by ks = Bexp(— r). In this growth regime, the growth rate depends on the temperature via the exponential factor. 

At high temperatures, the limiting factor is not the surface kinetics but the contribution of matter by the gas phase. The growth rate depends, therefore, on the coefficient hg whose variation with temperature is slow (hg oc T3/2). It is then considered that the growth rate in the regime of mass transfer is proportional to the concentration Cg. 

The experimental approaches [11-13] on the growth rate of silicon on silicon substrate confirm the presence of two growth regimes depending on the temperature a regime controlled by chemical kinetics for temperatures below 1,000°C and a regime controlled by mass transfer regime for temperatures above 1,000°C (Fig. 10.3). 

In the regime limited by the surface kinetics, adding a dopant gas to induce n-type or p-type doping causes an increase in the growth rate. On the contrary, in the regime limited by mass transfer, adding dopants in the reactive gas does not affect the silicon growth rate [16-18]. 

In the previous sections, studies of CBD kinetics were essentially based on the determination of an average growth rate, either independent of time ( linear regime ), or... 

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