PEZ

Production Effusion Cells PEZ are designed to meet the particular requirements of production MBE systems with higher throughput.
Their wide operating temperature range of 200-1400°C allows evaporation or sublimation of a large number of elements and compounds, including standard III-V and II-VI MBE materials such as Al, Ga, In, As, or Zn.

Besides standard filaments SF, hot-lip HL, cold lip CL and dual filament DF configurations are available, meeting the differing requirements of the evaporation materials. The picture on the right-hand side details a PEZ with dual filament.

The standard crucible material for the PEZ is PBN. PEZ cells are either equipped with conical or cylindrical crucibles, depending on the MBE chamber design, and offer precice flux reproducibility and excellent thickness uniformity.

Further improvements of source material utilization and flux stability can be achieved by using of a customized beam shaping insert in combination with a large capacity crucible. Crucible inserts not only reduce the effect of fill level-related flux shift, but also act as a thermal buffer virtually eliminating shutter transients (see Application for more details).

Similar to our standard effusion cells, the crucible is heated by a wire filament supported by PBN rings. The advantages of this heating assembly are described on page WEZ.

The consequent use of power and TC feedthroughs on separate DN16 CF flanges allows easy servicing. Completely closed power connectors with gold-plated contacts guarantee easy and safe handling of the PEZ.

For large scale production systems crucible capacities up to 1700 cm³ (and more ) are available.

The PEZ design offers enough flexibility to adapt to the particular requirements of UHV deposition applications with high throughput such as commercial fabrication of III-V semiconductor devices or thin film solar cell production.

The right-hand picture shows the PEZ 150-700-124-DF, a large production effusion cell with conical 700 cm³ crucible and dual filament. This cell is typically used for evaporation of III metals simultaneous on several semiconductor samples in III-V MBE production systems.

Application

The PEZ is recommended for elements and compounds evaporated or sublimated at temperatures in the range 200-1400°C, e.g. Al, Ga, In, As, Zn, etc.
Compared with our standard effusion cell WEZ, the PEZ is distinguished by a more robust cell design and the consequent optimization of many details leading to a further improvement of stability and reproducibility, as well as excellent reliability and easy servicing. The PEZ is thus ideally suited for production MBE systems.

For MBE applications that require a wide-area homogeneous growth, the use of conical crucibles (e.g. in cell type PEZ 63-40-51-K) is recommended. A compact hot lip filament improves the critical power management in the upper crucible zone by reducing the heater wire temperature, equivalent to less chemical corrosion. In addition, the more robust radiation shielding and cell heater housing as well as flange protection tubes reduce the risk of chemical corrosion and electrical short-circuits caused by liquid metals (gallium).

Especially designed for Ga or In deposition in III-V MBE systems, the PEZ with large cylindrical crucibles (130 cm³ or larger) can be equipped with a customized crucible insert.
The use of a very large crucible with a beam shaping insert combines the advantages of conical and cylindrical crucibles:

• The crucible insert provides conical beam shaping, resulting in minimized waste of material and excellent uniformity.

• Conical crucibles show the effect of fill level-related flux shift, due to the continuous changing of the evaporation material surface. This effect is widely reduced in PEZ cells with insert, because the apparent surface remains constant during a growth campaign.

• Shutter transients are a common problem for layer growth when using standard crucibles with wide orifice. The influence on the thermal stability of the molten material caused by shutter action is virtually eliminated by the crucible insert's function as a thermal buffer in combination with dual filament heating.

• Dual filament heating allows keeping the conical insert at higher temperatures which avoid material condensation. It is a mandatory feature when using inserts.

Large Capacity Ga/In PEZ cells feature a material efficiency up to 25% better than SUMO^TM type cells.
A PEZ with 130 cm³ crucible and insert is capable of holding a maximum Ga load of 500 g, depending on the actual mounting angle. With 1500 cm³ crucible the maximum Ga load is even increased to 5 kg.