НИЗКОТЕМПЕРАТУРНЫЕ ЯЧЕЙКИ

Temperature stability of a Low Temperature Effusion Cell @ 125°C

A standard effusion cell employs a single radiative heater element which surrounds the crucible. Since the crucible is open only at one end, however, the temperature is inhomogeneous along the central axis of the crucible and the temperature can vary strongly (by hundreds of degrees celsius) between the bottom and top of the crucible. As a result, considerable condensation is frequently observed at the mouth of the crucible. The diameter of the crucible is thus progressively reduced during the deposition process and can eventually become completely blocked. This phenomenon is especially severe for high vapor pressure materials which require low temperatures during operation.

ADDON low temperature (or HOT LIP) cells are designed with a hot zone at the lip of the cell to combat the temperature gradient. This is achieved through the combination of the hot zone geometry and heat shielding which acts to reduce heat loss through the I.R. transparent crucible lip. This design prevents recondensation
of materials at the mouth of the crucible and thus avoids the continuous decrease of flux and change in spatial distribution associated with such condensation.

Temperature stability at low temperature is a very important factor, as a slight change can produce a large difference in BEP for high vapor pressure materials.
This is especially true with II-VI elements like CMT or ZnS/ZnSe compounds, in which a composition change of less than 1% can dramatically affect the electrical
and optical properties of the epilayers. Results obtained by ADDON designed low temperature cells for long runs on thick CMT layers show very high stability in temperature and flux distribution.

INSERTS: For II-VI materials which often require very low evaporation temperatures, it is sometimes necessary to use internal baffles in the crucible to improve pressure/temperature conditions and avoid blocking. ADDON can advise you on appropriate configurations and realize special configurations.

Compatibility:
The cell comes in models fully compatible with existing systems manufactured by Varian VG, EPI, Perkin-Elmer, Ulvac and Riber. Other versions are also available (please provide us with details of flange size, connecting tube and in-vacuum length).

Thermocouples:
A double thermocouple is employed. Standard K type (Cr/A1) thermocouples which have a relatively high e.m.f. are installed as standard because they provide better stability at low temperatures (C type thermocouples or others are also available upon request).

Power Systems and Temperature Controller:
Most existing power units are compatible. ADDON models are recommended if a new power unit is needed.

Integrated shutter:
An integrated shutter mechanism can be fitted on most of the cells described here.

Integrated cooling circuit:
If necessary a water cooling circuit can be integrated on most of the cells described here.
VG compatible cells integrate the cooling circuit as a standard feature.

Filament:	One
Maximum Operating Temperature:	up to 750 °C
Maximum Outgassing Temperature:	850 °C
Temperature Stability:	better than +/- 0.1 °C
Thermocouples:	Double C type (W Re 5/26%)
MINIMUM MOUNTING FLANGE Crucible Capacity:	25 35 40 58 35CF / 70mm / 2.75" 60 70 85 125 150 63CF / 114 mm / 4.5"
In-Vacuum Diameter:	Crucible O.D plus 0.2 mm
In-Vacuum Length:	200 to 400 mm. Please contact us for other values.
Temperatures / Power Consumption:	See curves
Power Supply Connectors:	System or ADDON
OPTION:	-Other types of thermocouples -Integrated cooling circuit -Integrated shutter -Inserts
WARRANTY:	Two years: see product policy section

Thermocouples:
For high vapor pressure materials the K type is standard. C, D and others are also available.

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