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- Well suited for As, P, Se & S
- Reduces As / P consumption
- Improved efficiency due to rapid flux response:
As or P beam can be supplied / cut off quickly
- Lower background pressure in the MBE chamber
- Reduction of oxygen background as the source material can support higher temperature than in a standard cell without excessive material loss
- Improved precision, reproducibility & ease of flux control due to precise micrometer valve
- The potential to use either As4 or As2 on demand
- A large useful capacity (up to 2.5 kg of As
6 kg for the production model)
- Reduced contamination
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Valved Cracker Cells for Te or AS
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Solid source cracker cells are used to decompose evaporated polyatomic molecules into simpler species. This is achieved using a two-stage source, with each stage having different thermal characteristics. The first stage is simply a large capacity thermal effusion solid source. The flux produced by this stage passes into the second stage, which consists of a tubular cracking zone, which is maintained at a higher temperature so as to pyrolyze the evaporated species and, thereby, eradicate and untracked source molecules.
Solid material crackers are used primarily with elements which sublime as polyatomic species i.e. As, P, Sb, Se, S & Te.
In this kind of cell a valve is used to isolate the source charge from the growth chamber.
Valved Cracker Cells present the best alternative to standard effusion cells for elements which evaporate readily such as those in Group V.
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| An increase of 5° of the P white condenser corresponds to an increase of P2 flux (at a given setting of the valve) of about 75% |
VALVED CRACKER CELL FOR PHOSPHORUS
- prevents evaporation of solid P in the chamber during bakeout (Red P has a vapor pressure of 4 x 10-2 torr at 200°C).
- avoids the formation of white phosphorus in the MBE system since P2 condenses preferably on cold parts in the safer Pred form.
- allows opening of the Pred reservoir for reloading without system venting.
- improves the P beam purity because the source can be baked at high temperature before use and isolated from atmospheric pollution when the system is vented.
- easy P2 flux control: reproducibility and stability over several hours are better than 1%
- no flux burst on opening of the valve.
- high vapor pressure P charge outside the MBE system (no bakeout problems).
- compatibility with Ion/Ti sublimation pumping.
- 350 cc Pred capacity .
- large cracker and valve conductances for large BEP at low condenser temperature
- low condenser temperature to avoid Pwhite instabilities.
Due to the generation of the two forms (red and white) when solid P is vacuum evaporated use of the 3 Zone Vacuum Tight Valved Cracker Cell is the only working alternative to CBE.
This new ADDON cell solves all the problems which arise when Phosphorus is evaporated from a standard cell or cracker cell. The design combines the flexibility of a phosphine cell with the ease of use of a solid source cell.
When closed the valve fully isolates the charge from the chamber.
Leak tight all-metal valve for isolation and flux control .
Full modularity of the design for simple P charge loading, maintenance or further upgrading.
For P3 a thermal zone valved cracker cell is used, so as to avoid the Pwhite problems which were discovered and resolved by Briones in the early 90’s.
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| Material |
Capacity (cc) |
MBE System |
| RIBER |
VG |
Varian / Intervac |
Others* |
| Arsenic |
700 (1) |
VC700As-RI |
VC700As-VG |
VC700As-VA |
VC700As-AD |
| Phosphorus |
350
2500
4500 |
VC350P-RI
VC2500P-RI
VC4500P-RI |
VC350P-VG
VC2500P-VG
VC4500P-VG |
VC350P-VA
VC2500P-VA
VC4500P-VA |
VC350P-AD
VC2500P-AD
VC4500P-AD |
| Selenium |
700 |
VC700Se-RI |
VC700Se-VG |
VC700Se-VA |
VC700Se-AD |
| Sulfur |
700 |
VC700S-RI |
VC700S-VG |
VC700S-VA |
VC700S-AD |
| Mercury (#) |
14 kg |
V14Hg-RI |
V14Hg-VG |
V14Hg-VA |
V14Hg-AD |
| Antimony |
550 |
VC550Sb-RI |
VC550Sb-VG |
VC550Sb-VA |
VC550Sb-AD |
| Tellurium |
550 |
VC550Te-RI |
VC550Te-VG |
VC550Te-VA |
VC550Te-AD |
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- (1) Larger capacity available for all VG and Riber Production Systems consult ADDON.
- For all system, specify exact model.
- VG systems: Cracker Zone integrated water cooling in standard exept for Hg
- Other systems: specify system flange, cell length and if integrated water cooling is needed or not.
- # Mercury source: the effusion tube extremity is heated to avoid condensation not for cracking effect.
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