Silicon molecular beam epitaxy

Leong, Weng Yee (1985) Silicon molecular beam epitaxy. Doctoral thesis, City of London Polytechnic.


This thesis reports on the techniques used in the growth and doping of Si-MBE layers prepared in a commercial molecular beam growth system and in the evaluation of their electrical and crystallographic properties. A number of technological problems associated with flux monitoring, the flaking of excess Si deposits and the use of closed-cycle He cryopumps during system bakeout were addressed.

The electrical and crystallographic qualities of the undoped and doped Sl-MBE materials were assessed using preferential defect etching, four-point probe and Hall measurements, electrochemical CV profiling. Auger electron surface analysis, transmission electron microscopy (TEM), secondary ion mass spectroscopy (SIMS) analysis, spreading resistance measurement, and photoluminescence. The basic material grown was found to be of high quality and comparable to the Si-MBE material grown in other laboratories. Two electrically active contaminants, boron and phosphorus, were identified in our materials. The boron contamination was observed to occur at the substrate/epitaxial interface where the presence of an oxide layer prior to growth was apparently critical for its accumulation.

Two new techniques in co-evaporatIve doping in Si-MBE are reported. The use of co-evaporated boron doping was Investigated enabling the growth of Sl-MBE material with bulk-like mobilities and carrier concentrations up to 1x10(to the power of 20) cm(to the power of -3) and giving excellent dopant profile control over a range of growth temperatures. The second technique called Potential Enhanced Doping (PED) involves applying a substrate potential during layer growth which enhances Sb dopant incorporation coefficient by up to a factor of 1000. Doping transitions were obtained by stepping the substrate potential. Using the PED technique, a maximum Sb dopant concentration of 2-3x10(to the power of 19) cm(to the power of -3) at 850°C and dopant transitions as abrupt as 200A/decade were achieved. Possible mechanisms for the observed PED effect are presented.

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