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SUSI 63, silicon sublimation source on DN63 (O.D. 4.5") CF-flange

• Growth of thin Si layers
• Si Doping in III-V MBE (GaAs) with
  Fast and precise flux control
• Ultra high purity silicon filament
• Highly doped P- or As- silicon filament
  for special doping applications
• Water cooled electrical contacts
• Inner filament shielding with Si parts
• No ceramic parts in the hot zone
• Compatible with most MBE systems
• More than 12 years experience

The Silicon Sublimation Source - SUSI - was developed for growing thin Si layers, short period Si/Ge superlattices and Si/SiGe heterostructures.

The SUSI allows growth of high crystal quality thin epitaxial Si layers, not otherwise possible with PBN crucible effusion cells. It is also an optimal alternative to an e-beam evaporator, if highest purity, stable flux and low flux rates are required.

Our Si sublimation source provides a very clean and constant Si flux at a low growth rate. Maximum growth rates of 7 Å/min and total layer thickness of 5-10µm pure Si with one filament are reported. Therefore the SUSI is ideally suited to doping in III-V MBE and thin Si layer growth.
Special applications include boron and phosphorus doping in Si MBE. Highly doped Si source material is used in this case.


The main parts of the SUSI (silicon filament arch, silicon base plate, silicon shielding tube, silicon top plate and tantalum power contacts) are shown in the figures on the right.

Silicon filament and shielding parts of SUSI

The specially designed free standing silicon filament arch is directly heated by electrical current and is surrounded only by high purity silicon shielding parts.

Extreme heating of metal and ceramic parts is avoided by very effective water cooling of the electrical contacts, and by shielding the hot silicon filament completely with silicon only. No insulating ceramic parts are used in the hot zone.

As the sublimating filament is totally surrounded by Si shielding parts the SUSI provides an extremely clean Si flux. In a well designed Si MBE chamber a pressure in the 10^-10 Torr range is achieved while running the SUSI at maximum growth rate.

Highest purity silicon parts of SUSI:
filament arch, base plate, shielding tube, top plate

Application

The SUSI is used for Si epitaxy, especially growth of high quality thin Si layers, Si doping in III-V MBE and doping in Si MBE.

• Si Epitaxy and Growth of thin Si Layers
  The SUSI can be used as an alternative Si source to widely used e-beam evaporators, if highest purity, stable flux and an absolutely ion-free beam is required. The low growth rate makes SUSI an ideal source for high quality thin Si layers, whilst it is naturally less suited to the growth of thick layers.
  
  
• Si Doping in III-V MBE
  For doping in III-V MBE the silicon flux usually needed is considerably lower than 0.1 Å/min. The electrical current which provides this silicon flux rate is between 20 to 35 A for SUSI 40 and 40 to 50 A for SUSI 63.
  These values may be used as a guide to start calibration of the doping level as a function of the current.
  The low power operation guarantees a long lifetime without any servicing.
  
  
• Doping in Si MBE
  A very special application of the SUSI is the operation as a doping source for Si MBE growth by using a heavily boron or phosphorus doped silicon filament.
  Adjusting of the doping level is performed by changing the ratio of the flux rates between undoped silicon source and the boron / phosphorus doped silicon from the SUSI. There is no practical limit for very low doping levels since the ratio between the undoped silicon source and boron doped silicon from the SUSI can be changed very easily and quickly over a wide range by changing the SUSI operation parameters, due to it's direct heating and water cooling.
  
  
  • Boron Doping
    The source material for sublimation is boron doped to about 10²⁰ cm^-3.
    The maximum boron concentration in the epitaxial film is about 2x10¹⁹ cm^-3 (during silicon sublimation some boron segregates on the surface of the silicon filament).
    The maximum total thickness of the film which can be grown with one silicon filament in SUSI 40 is about 5µm (in SUSI 63 - 10µm) at a substrate distance of 200mm.
    The maximum doping level of 22x10¹⁹ cm^-3 is achieved by growing only with the SUSI.
    
    
  • Phosphorus Doping
    The source material for sublimation is phosphorus doped to about (3 to 4)x10¹⁹ cm^-3.

Reference

Publications based on samples grown with SUSI:

1. Encapsulation of phosphorus dopants in silicon for the fabrication of a quantum computer
   L.Oberbeck, N.J.Curson, M.Y. Simmons, R.Brenner,, A.R. Hamilton, S.R. Schofield; Appl. Physics Letters 82, 17 (2002)
2. Comparison of P and Sb as n-dopants for Si molecular beam epitaxy
   J.F. Nützel and G.Abstreiter , Journal of Applied Physics 78, 937-940 (1995)
3. Microscopic symmetry properties of (001) Si/Ge monolayer superlattices
   Eberl, K.; Wegscheider, W.; Schorer, R.; Abstreiter, G. Physical review b-condensed matter, (1991) 43, 6, pp. 5188-5191.
4. Group-IV element (Si, Ge and alpha-Sn) superlattices - low-temperature MBE
   Eberl, K.; Wegscheider, W.; Abstreiter, G.Journal of crystal growth, (1991) vol. 111, no. 1-4, pp. 882-888.
5. Transmission electron-microscopy of short-period Si/Ge strained-layer superlattices on Ge substrates
   Wegscheider, W.; Eberl, K.; Cerva, H.; Oppolzer, H. Applied physics letters, (1989) vol. 55, no. 5, pp. 448-450.

Technical Data

Dimensions

Specific Data

 LAST UPDATE: NOVEMBER, 2004

© 2003 Dr. Eberl MBE-Komponenten GmbH