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Compound dissociation K-cell
Gas dosers
MBE growth; GaP, GaInP, etc.
P doping in Si MBE
Arsenides
Dimer:tetramer ~1000:1
P2/As2:Ga >10
4
:1
Standard K-Cell controllers
Compound Dissociation K-Cell
Phosphorus, Arsenic - Low cost alternative to valved crackers
Although it has been known for many years that the thermal decomposition of GaP/InP and GaAs/InAs produce substantially P
2
and As
2
respectively(1), only recently has this method been seriously applied in MBE as a simpler, lower-cost alternative to two-zone valved crackers(2) which operate with elemental red phosphorus (P
4
) feedstock. On heating, red phosphorus sublimes and converts to the white P
4
allotrope, which must then be thermally cracked from a secondary buffer zone to produce the reactive P
2
species. In contrast, the CDK35 is a compound dissociation source consisting solely of a K-cell and a Ga trap. The source produces a beam of dimeric phosphorus/arsenic with extremely low parasitic Ga content and tetramer species.
The K-cell is simple to use and maintain and provides stable, reproducible deposition rates. It can be used for applications requiring high growth rates, such as phosphides; or for doping applications.
For GaP decomposition the dominance of P
2
over P
4
is ~ 1000:1 at a dissociation temperature of 950ÂșC. However, there is also a significant (and undesirable) contribution of Ga vapour at this temperature.
Figure 1 shows the partial pressures of Ga and P
2
using the source without the Ga trap. The P
2
/Ga ratio is only 6:1. Figure 2 shows the partial pressures of these species with the Ga trap fitted. By this means a P
2
/Ga ratio of ~10
4
:1 can be achieved (3).
Specification
Model
CDK35
In-vacuum diameter
34mm
In-vacuum length
200mm (standard)
Mounting flange
NW35CF
Operating K-cell temperature
to 1000
o
C<
Crucible
PBN - 35 cm
3
*
Power supply
Included
Water cooling
Included
Options
Shutter (NW63CF flange required)
* Higher capacity available on request
(1) Farrow, R.F.C.,
J. Phys D
.
7
pp2436 (1974)
(2) Song, J.D, et al.,
J.Cryst. Growth
237-239
pp1504 (2002)
(3) Oxford Applied Research mass spectra (unpublished)
Download brochure in PDF format:
CDK35
Last updated: 23rd July 2010
Copyright 2008 The Vacutec Group
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