DECO-D

Phosphorus Doping Source

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

• 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

The Phosphorus Doping Source 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.

Principle sketch of Ga-Trapping Cap Unit

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.

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.
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.

References

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

Dimensions

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

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.