MBE Components, Carbon Sublimation Source SUKO

SUKO

Carbon Sublimation Source

SUKO 40
  • Thermal sublimation of carbon from high purity graphite filament

  • Excellent growth of thin carbon films or Si-C alloys

  • Compatible with most MBE systems
  • Water-cooled electrical contacts

  • Inner filament shielding with pure pyrolytic graphite parts

  • No ceramic or metal parts in the hot zone
SUKO 40 Carbon Sublimation Source on DN40CF (O.D. 2.75") flange

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When the Carbon Sublimation Source SUKO was originally developed some twenty years ago, it was a breakthrough for growth of Si-C and Si-Ge-C alloys in silicon MBE. The SUKO still provides a preeminently clean and stable flux at a low deposition rate of up to 2 Å/min. Since then it has also been successfully applied in a variety of other research fields, e.g. graphene formation.

A special carbon doping version SUKO-D was thoroughly redesigned in collaboration with Prof. W. Wegscheider, formerly University of Regensburg, Germany. It is a highly optimized source for carbon p-type doping in III-V MBE.

Sublimation of carbon from a resistance heated graphite filament requires temperatures up to 2300°C. The entire SUKO heater assembly therefore consists of pyrolytic graphite (PG) parts.
Screws, washers, contacts, plates and shielding tube, all made from PG, protect and shield the hot filament. A very effective internal water cooling of the electrical contacts avoids overheating of these parts, allows a rapid change of the flux rate and provides for a short adjusting time.

Most other carbon cells are built with metal or ceramic parts in the heater area. These materials however generate CO and other residual gases when used in the hottest zone.
The consequent design of the SUKO prevents extreme heating of any non-graphite parts, thus virtually eliminating such undesirable outgassing.

SUKO assembly

Main parts of the SUKO assembly

At typical operation conditions the SUKO graphite filament is glowing at a temperature of about 2200°C. Especially for heat sensitive substrate materials it should be taken into account that a lot of radiation is impinging on the surface of the substrate during exposure.

The SUKO already includes water-cooled power feedthroughs and contacts to provide ultra-pure operation conditions. An additional surrounding cooling should be provided to avoid overheating of stainless steel parts within the UHV chamber.
In case the chamber has no internal (cyro-)cooling panel, separate water cooling shrouds CS are recommended for all SUKO models. Cooling shrouds can also be equipped with an integrated rotary shutter.

Hot graphite filament

Close-up view of hot SUKO graphite filament


Application

The SUKO is most frequently used in III-V MBE and Si MBE for growth of Si1-xCx or Si1-x-yGexCy alloys. When growing atomically thin carbon layers in Si MBE, the maximum growth rate at a distance of 200mm should not exceed 1Å/min.

In general, the electron mobility turns out to be comparable to those achieved by Be doping. Optical, REM and x-ray studies have all confirmed the excellent morphology of the layers.

Due to its outstanding properties, particularly with regard to flux stability and reproducibility, the SUKO today is also applied for a number of other applications, e.g. investigation of graphene, carbon doping in III-V MBE, etc. See DECO-D for details on carbon doping.

In contrast to carbon gas sources no interaction with MBE equipment or any memory effect is observed while operating the SUKO.

Over the operating time the filament naturally becomes thinner, whereby the flux rate at a given current gradually increases. Tthe current should therefore be recalibrated and eventually reduced from time to time to keep the flux rate constant.

The lifetime of a graphite filament strongly depends on the control of the flux rate. This is especially important when operating at flux rates close to the maximum rate of the respective SUKO model. A runaway increase of the flux rate can result in a premature burning out of the filament. Under normal conditions a maximum total carbon layer thickness of 5µm with one filament is reported.

For Carbon Sublimation Sources optimized for doping applications please refer to our specialized source type SUKO-D.


References

Several publications based on samples grown with SUKO sources are listed in section References / List of Publications.


Technical Data

Filament type high purity graphite filament
Filament shielding filament completely shielded with PG parts
Thermocouple W5%Re/W26%Re (type C)
Operating temperature max. filament temperature 2300°C
Bakeout temperature 250°C
Electrical contacts water-cooled (4x Swagelok fitting connection O.D. 6mm); water flow min. 30l/h
Cooling separate water (or LN2) cooling shroud
Options integrated rotary shutter (S)


Dimensions

    Schematic drawing SUKO   Schematic drawing of the Carbon Sublimation Source SUKO

(drawing shows SUKO 40)



Specific data

For general information on CF mounting flanges see Flange and Gasket dimensions.

[mm] / [mm] [W] / [A] [Å/min] Product code
SUKO 40 - LxxxD36 455 / 75 0.5 PS 20-76
SUKO 63 - S - LxxxD55 950 / 100 2 PS 20-120
SUKO 100 - LxxxD95 5000 / 100 10 PS 60-100
* rotary shutter possible on same flange
** maximum growth rate at 100mm distance
*** specify UHV length L with order


Product code:

e.g. SUKO 63-S-L300D55

is a carbon sublimation source on DN63 CF-flange with shutter, in-vacuum length 300mm and diameter 55mm.