DECO

The Decomposition Source DECO is an ultra-pure source for P₂ based on the decomposition of GaP. It is an affordable and easily operated alternative to valved phosphorus sources.

Adapted from WEZ and PEZ effusion cells, the simple construction of the DECO with its specially designed Ga-Trapping Cap Unit maintains the advantages of easy installation, full compatibility to all MBE systems, high reliability and low costs of ownership. 
Operating the DECO is similar to usual effusion cells and does not require any complicated mechanical valves or controllers. Compared to frequently used valved phosporus crackers, the deposition of white phosphorus (P₄) in the growth chamber is significantly reduced due to the direct generation of pure P₂ from GaP.

Two main fields of application for the DECO have emerged: the source can be built for growth applications offering elevated evaporation rates and large crucible capacities, or optimized for special doping applications (DECO-D), e.g. phosphorus doping in Si MBE, with a reduced cell shutdown time. 

The heater of the DECO consists of a Ta wire filament supported by PBN rings, similar to standard effusion cells. This design guarantees minimum outgassing at operation temperature in combination with excellent reliability, long-term stability and extended lifetime.
PBN is invariably applied As crucible material for GaP decomposition.

Ga-Trapping Cap Unit

The DECO source features a unique Ga-Trapping Cap Unit system which provides a very pure P₂ beam by decomposition of GaP. The idea underlying that unit is the sublimation of phosphorus from GaP at rather moderate temperatures at which gallium has only a low vapor pressure. By special baffle plates parasitic Ga atoms are efficiently separated from the P₂ beam, thus producing a very pure P₂ flux.

The Ga-Trapping Cap Unit is a simple but effective design consisting of only a small number of well-designed parts which are mounted onto the PBN crucible without additional tools or holders. For source maintenance and crucible refilling the unit is likewise easily removable.

Upon special request, a complete Ga-Trapping-Cap Unit is available as a product of its own, for retrofitting standard effusion cells. 
Inquire for further information on compatibility.

• operating temperatures 900-1200°C for growth applications

• precise adjustment of P₂ incorporation into GaAsP. GalnAsP, etc., compound layers

• P₂/P₄ ratio about 150 : 1

• very low parasitic Ga flux (P : Ga > 10⁵); 
  (P : Ga > 10³ without Ga-Trapping Cap Unit)

• high efficiency: about 20 g P in GaP for 100µm film thickness

• marginal white phosphorus accumulation in MBE system

• no additional safety facilities needed in contrast to PH₃, AsH₃ or valved elemental phosporus crackers

• no bakeout necessary before opening the system

• compatible with standard III/V solid source MBE