Cracking Efficiency of Hydrogen with Tungsten Filament in Molecular Beam Epitaxy

Atomic hydrogen is known to exert various important effects on the growth of semiconductors in molecular beam epitaxy (MBE). In this work, the cracking efficiencies of hydrogen molecules into atomic hydrogen with a hot tungsten (W) filament have been experimentally determined. Hydrogen atoms recombine at the surface of a heated platinum detector to form molecules releasing the heat of reaction, which results in a temperature increase of the platinum detector, and the cracking efficiencies of atomic hydrogen can be determined by considering the enthalpy of atomization. The cracking efficiency increased exponentially with W filament temperature. At a filament temperature of 1600° C and a H2 gas flow rate of 1.5 ccm for example, the cracking efficiency was determined to be about 1.5% or equivalently, the number of hydrogen atoms resulting from cracking was 2×1016 cm-2s-1 at a H2 pressure of 1.87×10-2 Pa.