The absolute cracking efficiency of a commercial atomic hydrogen source is found to be as great as 30%. Negligible recombination of atomic hydrogen into molecular hydrogen occurs in the molecular beam epitaxy chamber. The cracking process can be accurately modeled as an equilibrium process. An atomic hydrogen flux impinging on the surface of GaAs lowers the oxide desorption temperature by similar to 100 degrees C. At temperatures up to 700 degrees C, atomic hydrogen does not enable the thermal desorption of AlxGa1-xAs oxides for x>10%-20%.