New features in Virtual Reactor 4.8 with respect to Virtual Reactor 4.6

Fixing Errors

• Errors found in the older release have been fixed. Robustness of the code operation was increased.
• The computation procedure was optimized to reduce the computation time and memory usage. In particular, the computation of mass transport accounting for the crystal faceting was noticeably accelerated.

Error Diagnostics

• The error diagnostics was made more detailed and clear.
• Divergence of the heat and mass transfer solution is now identified at earlier stages, which is provided by analyzing the final residuals when the computation stops at reaching the maximum number of iterations.

New features in Virtual Reactor 4.6 with respect to Virtual Reactor 4.4
 

Assigning the Materials

A new interface of the specification of the materials properties has been implemented into Virtual Reactor 4.6.

In the previous version of Virtual Reactor, the materials database was only used as an external source of materials whose properties could be copied to the blocks, so that the actual values of the material properties used in the computations were those specified in the corresponding blocks.

In Virtual Reactor 4.6, the properties are always stored in the materials rather than in the blocks. Each block now has a reference to its material. So if the user changes the properties of a material in the database after he assigned this material to some blocks, he does not need to reassign the block properties.

Using references to materials provided an easy and pictorial assigning materials to the blocks. The user can select a material in the list of available materials and just click all the blocks to which the material should be assigned with left mouse button. The material is assigned to all needed blocks.

The blocks of the same materials are filled with the same color in the Graphics Window, which provides a clear identification of all blocks in the Graphics Window. A new block to which no material is still not assigned is not filled, which provides a clear identification of such blocks.
 

The Mass Loss Model

A new model predicting the total internal pressure and the mass loss has been implemented.

To describe semi-opened growth systems, two individual models are introduced: model of porous walls and model of thin slits on the contacts of adjacent crucible parts.

• Model of the porous wall deals with microscopic pores assuming the mass transport to occur under free-molecular conditions. This model is designed to describe mass transport in a SiC system with crucible made of porous graphite.
• Model of the thin slit deals with relatively large channels assuming the mass transport to occur under diffusion conditions. This model is designed to describe mass transport in a system with crucible made of dense materials.

So two different types of the mass transport boundary conditions are available:

• Porous Wall. A boundary type that represents a solid surface permeable for the convective and diffusion mass transport through the pores. If the interface of the growth cell with the crucible is of Porous Wall type, the total pressure in the growth cell is calculated by the code.
• Thin Slit. A boundary type that represents a small opening at a non-tight contact of adjacent solid parts of the crucible permeable for the convective and diffusion mass transport.

As a result, in the case of using the porous wall model, the average partial pressure of the carrier gas in the growth chamber is equal to the external pressure, while the pressure drop is caused by the reactive species partial pressures. In case of using the slit model, the partial pressure of the carrier gas in the growth chamber may vary from in a wide range.
 

Multi-Coil Heating

Module "Two-coil RF Heating" for modeling of heat transfer in a growth system heated by two inductor coils has been implemented into Virtual Reactor.

Virtual Reactor is supplemented by an option allowing the user to model the heat transfer in a growth system heated by several inductor coils with temperature monitoring made in several reference points. Normally, this should be used to model systems with two coils.

The user can prescribe two independent inductor coils, specifying the current frequency and generated power for each coil. Then the code computes the temperature distribution in the whole system. In addition, using two coils allows temperature fitting at two reference points. In this case, the code automatically adjusts the power generated by each inductor to meet the required temperatures.

Each coil may have an arbitrary number of turns (windings). An individual turn of any coil is represented by an Inductor block. All inductor blocks that have the same material are considered as blocks of the same coil. Blocks with different material are considered as blocks of different coils. The number of coils in the system is determined as the number of Inductor materials assigned at least to one Inductor block.

For each coil the user can either assign the total power generated in the coil or specify that the power should be varied to maintain temperature in the reference points. To provide the temperature fitting, the number of reference points should not exceed the number of independent heaters (coils or resistive heaters).