VACS

The Valved Arsenic Cracker Source VACS is designed for high performance growth of III-V materials.
The VACS is highly specialized for As₄ or As₂ sublimation and combines large crucible capacity of 300 cm³, 500 cm³ or for industrial applications even 2000 cm³ with precise and fast flux control. A flux control range of more than two orders of magnitude is provided by the integrated valve mechanism. The typical on/off ratio is about four orders of magnitude.

The valve unit can be operated manually or with an additional valve control unit (MVCU) which controls the valve position by an external analogue voltage (0...10V), see picture on the right.
The integrated water cooling shroud and the use of selected materials for cell and valve unit guarantee high purity operation conditions. The operation mode of the source can be easily changed from As₄ to As₂ growth by the operation conditions of the integrated cracker unit.

The special design allows an easy refilling of the crucible from the backside without removing the cell from the chamber. It is also not necessary to completely empty the reservoir before refilling it. For refilling it is recommended to prepare a few cylindrical blocks with 1/3 or 1/4 height of the reservoir.  This simplifies your maintenance work and saves your time.

The typical valve characteristic, i.e. the beam equivalent pressure (BEP) as a function of the valve position, is shown on the right. The graph indicates the wide flux range of more than two orders of magnitude which is smoothly controlled on a wide value position range of several millimetres, when operated with a MVCU. The MVCU has a spatial resolution of 1/100 mm. This smooth operation condition guarantees a precise and reproducible flux control for your application. Together with a high motor speed of 10 mm/s a fast control is reached.

The design of the valve mechanism is schematically illustrated on the right side. It provides a large cross section opening which allows very good pumping of the As reservoir. The robust wide angle valve design effectively elimitates the chance of locking, which is a frequently observed problem for needle valves.

The VACS has proven to be a very reliable As source in the field. It is compatible to commonly used industrial and research MBE systems.

The large version VACS 150-2000 with 2000 cm³ crucible capacity (see picture on the right) is especially designed for industrial applications. It is particularly suitable for MBE systems such as OCTOPLUS 600 and OCTOPLUS 800.