Boron doping using compound source

Abstract

Boron doping has been realized in silicon molecular beam epitaxy using HBO 2 or B 2O 3 sources with the usual Knudsen cell. Carrier concentration could be controlled from 5×10 15 cm −3 to 3×10 20 cm −3 by changing the crucible temperature. From a comparison between activation energy for vapour pressure and carrier concentration dependence on crucible temperature, it was concluded that boron evaporated in the form of HBO 2 molecules from HBO 2 source. The boron profile, achieved by Knudsen cell shutter opening and closing, was sufficiently steep. The oxygen concentration in the epitaxial film depended on the growth temperature. Above 700°C, the oxygen concentration decreased to less than the detection limit of secondary ion mass spectroscopy, 10 18 cm −3. Fabricated p-n junction diodes showed very good rectification characteristics and the n factor was 1.07. These results make it possible to use boron as the p-type dopant in silicon molecular beam epitaxy without using ion embedding or a very high crucible temperature. For the applications of this boron doping technique, double-drift-type IMPATT diodes, bipolar transistors with a thin base layers, and Ge x Si 1− x narrow bandgap base heterobipolar transistors were fabricated.