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.
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)]
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.|
There are several publications based on P-doping in Si MBE with DECO-D sources.
|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|
|Cooling||integrated water cooling or separate cooling shroud|
|Crucibles||10-35 cm³ PBN crucibles|
|Options||integrated water cooling shroud (K), integrated shutter (S)|
|Schematic drawing of the GaP Compound Source
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|
|***||specify UHV length L with order|
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.