BORON DOPING USING COMPOUND SOURCE

Boron doping has been realized in silicon molecular beam epitaxy using HBO2 or B2O3 sources with the usual Knudsen cell. Carrier concentration could be controlled from 5×1015 cm-3 to 3×1020 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 HBO2 molecules from HBO2 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, 1018 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 GexSi1-x narrow bandgap base heterobipolar transistors were fabricated. © 1990.