MBE Components, Valved Arsenic Cracker Source VACS

VACS

Valved Arsenic Cracker Source

VACS 63-300
  • Compatible with all MBE systems

  • Crucible capacity 300 cm³ or 500 cm³

  • Large valve opening

  • Precise and very fast flux control

  • Easy handling and refilling procedure

  • Integrated water cooling shrouds

VACS 100-300 valved arsenic cracker with DN63CF (O.D. 4.5") mounting flange (using a VADP 100-63 adapter), 300 cm³ crucible, cooling shroud and motor drive

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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 or 500 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 VACS offers a relatively large valve opening which allows improved pumping of the As reservoir in open valve position.

MVCU with motor drive

Motorized Valve Control Unit MVCU with motor drive

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. This simplifies your maintenance work and saves your time.

BEP vs. valve position

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. 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 and is compatible to commenly used industrial and research MBE systems.

VACS valve design

Schematic illustration of the VACS valve design

Application

The VACS is used for As4 or As2 sublimation in III-V MBE.
Large crucible capacity (300 cm³ or 500 cm³), fast and precise flux control and easy handling for maintenance and crucible refill make the VACS ideal for smaller production MBE systems as well as for higher throughput research MBE systems.
BEP vs. time

BEP vs. time, with valve on and off (cell temp. 390°C / cracker temp. 600°C).
The motorized valve control allows to adjust and switch the As2 flux within seconds within about 3 orders of magnitude
SIMS of GaInP on GaAs buffer layer

SIMS of GaInP on GaAs buffer layer on (100) GaAs substrate with VACS and VGCS applied
 
Very sharp transitions of As are achieved by application of VACS and VGCS sources at one deposition run. 300nm GaInP are deposited on a GaAs buffer layer on a (100) GaAs substrate. Due to the fast flux control properties of the valve unit the As concentration in the GaInP layer is at its detection limit, i.e. three orders of magnitude below the GaAs level, which is demonstrated by the top right SIMS measurement. In return, P is sharply reduced on the GaInP/GaAs interface.


Technical Data

Filament type 2 separate heater-circuits (cell/cracker)
Thermocouple W5%Re/W26%Re (type C);  2 thermocouples (cell/cracker)
Operating temperature cell crucible: 300-400°C; cracker: 450°C (As4-mode) - 1100°C (As2-mode)
Outgassing temperature cell crucible: 500°C; cracker: 1200°C
Bakeout temperature 250°C
Cooling integrated water cooling shrouds
Crucibles 300 or 500 cm³
Flux control
integrated valve unit
Valve control hand control, or motor drive with control unit MVCU



Dimensions


Schematic drawing VACS
Schematic drawing of the Valved Arsenic Cracker Source VACS

(drawing shows VACS 100-300 with VADP adapter)



Specific data

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

images/header_nominal_capacity.gif
[cm3] [mm] / [mm] [W] / [A] Product code
VACS 100* - 300**- LxxxD57 cell: 200 / 6
cracker: 300/ 10
2x PS 70-10-C
VACS 100*- 500**- LxxxD57 cell: 300 / 6
injector: 300 / 10
2x PS 70-10-C
* other mounting flange diameters feasible in combination with VADP adapter flanges (on request)
** other capacities on request
*** specify UHV length L with order

Product code:

e.g. VACS 100-300-L290D57

is a valved arsenic cracker source on DN100 CF flange with 300cm³ crucible capacity and UHV-length 290mm.