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Michaela Brade
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Gas mixture analysis and reactor optimization

Gallium nitride (GaN) single crystals with their unique physical properties become increasingly importance in optoelectronics as wells as in high-temperature, high-frequency and high-power transistor material. The mechanisms during the growth process are complicated and require fundamental insights to minimize unwanted defect formation in the crystal lattice structure. Therefore the accurate metering of the gas concentrations in the reactor chamber and the sample stage is crucial.


Hydride vapor phase epitaxy (HVPE) is one of the most promising methods for flawless production of high quality GaN wafer. The gas concentration in a HVPE reactor chamber should be investigated as a function of different gas impact velocities, temperatures and reactor heights.


For analysis of this issues different FEM simulations were execute on a model reactor with variable geometry. Here, particular the area of the gas inlet was analyzed more in detail. Thereby the flow, gas concentration and temperature in the reactor and in the area of the substrate are of interest. For the calculation of this models meshes with common parameters were generated.


Figure 1 shows a cross section of the reactor with on overlying flow profile.  From the profile it is evident that the point with the highest flow rates is resulting from the profile of the nozzle on the inlet of the gas. The flow decreases due to the enlargement of space behind the inlet. The resulting flow rate affects the temperature in the reactor and varies in the area of the substrate holder. The faster the gas flows into the reactor, the lower the temperature. A dispersion of the inflow can generate an uniform temperature distribution at critical areas of the reactor chamber whereby an equal-shaped growth can be achieved. 

Advantages of FEM Simulation

  • Efficient design of reactor chamber
  • Control of the temperture in the reactor is possible
  • Determination of parameters for optimal growthn

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