MBE Components, Dopant Source DECO-D

DECO-D

Phosphorus Doping Source

DECO-D 40-10-22-KS
  • 1020/cm3 n-type doping in Si/SiGe MBE

  • P-doping through GaP decomposition

  • High P incorporation rate

  • Minimum memory effects

  • Easy to install and to operate

  • Sharp doping profiles

  • Precise and fast flux control

DECO-D 40-10-22-KS Phosphorus doping source, on a flange DN40 CF (O.D. 2.75"), with 10 cm³ PBN crucible and Ga-trapping PBN cap


The Phosphorus Doping DECO-D is an ultra pure source for P2, based on the decomposition of GaP. At typical operation temperatures of about 600°C - 700°C GaP is essentially decomposed to Ga and P2. Additional cracking is not necessary and the accumulation of P4 (White Phosphorus) is reduced to a minimum.

The simple construction of the DECO-D, based on our WEZ and PEZ cells, and the specially designed Ga-Trapping-Cap System have the advantages of easy mounting, full compatibility to all MBE systems, high reliability and low cost. The operation of the DECO-D is comparable to usual effusion cells and does not require complicated mechanical valves and controllers. MBE-Komponenten GmbH has developed special sources based on the Ga-Trapping-Cap System. We build the DECO-D optimized for special doping applications, e.g. as phosphorus doping cell for Si MBE with a reduced cell shutdown time.

The heater of the DECO-D is designed very similarly to the WEZ-heater which consists of a Ta wire filament supported by PBN rings. Crucible material is PBN. With this design minimum outgassing at operation temperature is achieved, in combination with excellent reliability, long-term stability and extended lifetime.

Excellent operation temperature stability of ±0.1°K is achieved by an improved design of the thermocouple assembly. This assembly touches the crucible near the base. The direct touch technique and the use of double pairs of TC-alloy wires ensure a reproducible and stable measurement of the real crucible temperature.

Ga-Trapping Cap Unit

The DECO source features a unique Ga-Trapping Cap Unit system that 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 negligible 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.

Ga-Trapping Cap Unit
Principle sketch of Ga-Trapping Cap Unit

Equilibrium pressures of GaP, Ga and phosphorus
Equilibrium pressures of the components along the metal-rich boundary of the field of solidus of a Ga-P system [R.F.C. Farrow, J.Phys. D, 7, 2436 (1974)]

 

  • 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


Application

Typical applications of our DECO-D phosporus doping source are high level and sharp delta-doping with Phosphorus in Si/SiGe MBE. Small crucible charges, large double layer shutters, integrated water cooling and reduced shielding allow a fast shutdown of the cell after the doping. High 1020/cm3 doping and sharp delta-doping have been reported in literature applying the DECO-D from MBE-Komponenten GmbH. Due to its small dimensions and easy operation the DECO-D is ideally suited for all types of MBE systems.

Single crystal GaP material with a purity >6N is recommended as source material.

The DECO-D has been successfully operated in many MBE laboratories worldwide. The following three figures demonstrate the unique performance of devices fabricated by means of the DECO-D.

The figure below shows a sharp P-doping profile in a Si layer with two P-delta-layers. The experiment was performed at the Universät der Bundeswehr in Munich, in the group of Prof. Eisele.

P-doping profile
SIMS measurement of phosphorus delta-doping in Si-MBE with a DECO-D 40-10-22-KS; (Data courtesy of C.Tolksdorf, Physics Institute ET9, Uni-BW Munich)


The figure on the right shows an I-U characteristic with a record high peak-to-valley current ratio of a Si/SiGe Esaki diode. The data are from R. Duschl et al., Appl. Phys. Lett. 76 (2000) 879, measured at the Max-Planck-Institute for Solid State Research in Stuttgart.  I-U characteristic
On the last figure a SIMS profile of a sharp p-n junction in a Si/SiGe/Si Esaki diode decice is presented. The structure was grown at the Max-Planck-Institute for Solid State Research in Stuttgart, in the group of Dr. O. Schmidt. It shows a record high peak-to-valley current ratio. SIMS profile


References

There are several publications based on P-doping in Si MBE with DECO-D sources.

Technical Data

Filament type Ta wire heating filament, optimized for doping application
Thermocouple W5%Re/W26%Re (type C); type K on request
Operating temperature 600-700°C for doping applications
Outgassing temperature 1500°C
Bakeout temperature 250°C
Cooling integrated water cooling or separate cooling shroud
Crucibles 10-35 cm³ PBN crucibles
Options integrated water cooling shroud (K), integrated shutter (S)

Dimensions

Schematic drawing DECO Schematic drawing of the GaP Compound Source

(drawing shows
DECO 40-35-34-S)


Specific data

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

[cm³] [mm] Type [mm] / [mm] [W] / [A] Product code Product code
DECO-D 40 - 10 - 22 - S - C - P - LxxxD34 120 / 6 PS 30-10 PBN 10-22
DECO-D 40 - 10 - 22 - K S - C - P - LxxxD36 120 / 6 PS 30-10 PBN 10-22
DECO-D 40 - 35 - 34 - S - C - P - LxxxD35 180 / 7 PS 30-10 PBN 35-34
DECO-D 40 - 60 - 37 - C - P - LxxxD38 240 / 8 PS 30-10 PBN 60-37
DECO-D 63 - 35 - 34 - K S - C - P - LxxxD60 180 / 7 PS 30-10 PBN 35-34
* rotary shutter possible on same flange
** PBN standard
*** specify UHV length L with order

Product code:

e.g. DECO-D 40-10-22-KS-C-L277D36

is a phosphorus doping source on DN40 CF-flange for a 10cm³ crucible (lip Ø 22), integrated water cooling shroud, shutter, type C thermocouple, in-vacuum length 277mm and diameter.