Hot-Lip Cell: Low temperature cell

Please contact us to find the best suitable model for your needs: webrequest@episerve.de

* Reduction of condensation at the crucible mouth
* Excellent beam reproducibility and stability
* Avoids the blocking of the cell observed with
* materials like Zn, Te, Sb, Se, Pb, ZnTe, ZnS, PbTe...
* Hot zone: designed for temperatures
* under 700°C i.e. high vapor pressurematerials
* Inserts and special configurations for II-VI materials
* Compatible with most MBE systems
* Compatible with commonly used power units
* Optional integrated / cooling shutter
* Wide range of crucible capacities
* Modular design
* Double thermocouple
* Operating temperatures < 750°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

 

 

 

 

Temperature stabililty of a LT-Effusion Cell @ 125°C

 

ADDON Innovation
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)

Specifications:
Filament: 1 filament
Maximum 0perating temperature: 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: for crucible capacity 25 35 40 58 ccm 35CF / 70mm / 2.75", for crucible capacity 60 70 85 125 150 ccm 63CF / 114 mm / 4.5", Higher capacities on request
In-vacuum diameter: Crucible O.D plus 0.2 mm
In-vacuum length: 200 to 400 mm. (other on request)
Temperatures / power consumption: See curves
Power supply connectors: System or ADDON via universal UNIPLUG

Options: Other types of thermocouples, Integrated cooling circuit, Integrated shutter, Inserts