Page 17 - RSE - Results of the Apollon Project

Results of the APolloN PRoject ANd coNceNtRAtiNg PhotovoltAic PeRsPective

One objective of the optimization was to fnd the ideal diameter for this injector in conjunction with the
optimal temperature profle the gas experiences when fowing from the injector to the exhaust. Here, the different
decomposition kinetics of the precursors IBuGe, TMGa, TMIn, TMAl, TBP, TBAs, PH and AsH have been taken into
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account and the temperature profle tuned accordingly.
Using numerical CFD computation a relatively large injector was found to be the optimal solution. This injector
carries the reactant precursors relatively far into the reactor chamber, exposing them to decomposition temperatures
relatively late and keeping the free surface of the reactor walls and susceptor small, which in turn reduces the carry-
over from a group-IV layer to the III-V semiconductor and vice versa.

Experimental Results from the APOLLON Project for MJ Solar Cell Growth

temperature tuning Capability

The reactor was built and thermally characterized using advanced pyrometry and thermal imaging techniques.
After pre-qualifcation the reactor was installed into an existing AIX 2800G4 system at RSE with all required upgrades
to the thermal control and gas mixing system (see Figure 7).
The temperature tuning capability has been demonstrated on Ge wafers over which a slightly lattice mismatch
InGaP single layer was deposited, taking the growth of an entire TJ solar cell structure into account, too.

FiguRE 7. AIX 2800G4 APOLLON reactor installed in RSE clean room

A strained InGaP/Ge growth was designed in order to introduce a curvature in the wafer and analyze the evolution
of temperature difference between the center and the edge of the wafer during the temperature tuning experiment.
For this purpose, advanced diagnostic “in situ” tools were used that allowed wafer curvature to be measured during
the growth along with the true (emissivity corrected) wafer surface temperature in the wafer center and edge (see
Figure 8).

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