CARS in situ diagnostics in MOVPE: The thermal decomposition of AsH3 and PH3

Abstract

Coherent anti-Stokes Raman Scattering (CARS) is used to study the thermal decomposition of AsH3 and PH3 in a horizontal reactor for metalorganic vapor phase epitaxy (MOVPE) of III/V compound semiconductors. Both in situ diagnostics and ex situ sampling experiments are considered. The decomposition temperatures obtained from in situ experiments are much lower (300 to 400 K) than those measured by ex situ techniques. The ex situ data compare well to previously reported observations. The results indicate that the thermal decomposition of AsH3 and PH3 is complex involving gas phase and surface reactions. The large difference in decomposition behavior between the two measuring techniques also demonstrates the importance of in situ diagnostics and the difficulty in ex situ monitoring of MOVPE species concentrations. No change in AsH3 or PH3 decomposition behavior is observeed with the addition of TMG or TMI. Molecular hydrogen is detected as a decomposition product, however in concentrations which are lower than expected from complete hydride decomposition.