MOCVD reactor

Fig. 3. Schematic of three commonly used types of MOCVD reactors where the arrows indicate gas flow (a) vertical rotating disk where (— represents an inlet to promote a laterally uniform gas flow, (b) planetary rotation, and (c) hori2ontal.

Figure 1 Illustrates two general MOCVD reactor configurations, the horizontal reactor and the axlsymmetrlc vertical reactor. The reactant gas (ASH3, Ga(CH3)3 and Al( 013)3) enters cold and heats up as It fiows toward the substrate where a solid film of AlGaAs Is being deposited. The chemical transformations Involved In the deposition process may occur both In the gas phase and on the surface of the growing film.

Figure 1. Two typical MOCVD reactor configurations (a) horizontal reactor (b) vertical reactor.

Since variations In the pressure Induced by fluid dynamic effects are negligible for MOCVD reactor flows, the Inlet pressure, Pq, Is used. In formulating the energy balance, the contributions from pressure changes, viscous dissipation and Dufour effects may neglected for MOCVD conditions (14.15) so the equation becomes ... 

Figure 2. Computed grids for four different shapes of a vertical, axlsymmetrlc MOCVD reactor.

In the following sections we describe simulation results providing new Insights Into general MOCVD reactor behavior as well as the two major practical considerations, film uniformity and Interface width. 

The growth of superlattices Is one of the key Issues In MOCVD reactor analysis and design. In addition to growing highly uniform, pure Aims one must be able to form sharp or accurately graded Interfaces between... 

D.I. Fotiadis, A.M. Kremer, DP. McKenna, and K.F. Jensen. Complex Flow Phenomena in Vertical MOCVD Reactors Effects on Deposition Uniformity and Interface Abruptness. J. Cryst. Growth, 85 154—164,1987. 

FIGURE 4 Schematic diagram of a typical large-scale highspeed vertical rotating-disk MOCVD reactor chamber including a simplified view of gas flow in a vertical RDR. The inlet gas stream contains the precursor flows and the main carrier gas flow. Typically, the Column V and Column III sources are kept separate until a few inches above the heated susceptor. 

FIGURE 5 Schematic diagram of a typical large-scale horizontal gas foil Planetary MOCVD reactor chamber. The precursor gases are injected in the center of the rotating wafer carrier and the gas flows horizontally over the individually rotating wafers. 

Future advances in precursor purity and manufacturing technology, real-time monitoring of chemical reactions, MOCVD reactor chamber design, computer-controlled epitaxial growth systems, detailed chemical process models, and real-time process control will lead to improved process efficiencies, reduced hazardous waste, and enhanced device reproducibility, yield, and performance. The future of MOCVD is certainly bright. We are on the frontier of a great expansion of the abilities of MOCVD to provide materials for products that improve and expand the human experience on earth, under the oceans, and in space. 

Stringfellow and coworkers showed that the Bu AsHj and BU2ASH pyrolyses were accelerated by an increase in the t-butyl radical concentration. The independent t-butyl radical source was azotertiary-butane (BujNj). The self-pyrolysis temperatures for 50% decomposition were reduced to 350 °C for BujAsH and 300 °C for Bu AsH2 under the gas-flow conditions of MOCVD reactors. On the basis of analyses of the products of the pyrolyses they proposed the plausible mechanisms shown in Schemes 4 and 5. 

Visser EP, Kleijn CR, Govern CAM., Hoogendoom CJ, Giling LJ (1989) Return flows in horizontal MOCVD reactors studied with the use of Ti02 particle injection and numerical calculations. J Crystal Growth 94 929-946... 

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