Hydrogen in gallium nitride grown by MOCVD

The role of hydrogen in gallium nitride was studied on thin films of GaN on sapphire prepared at substrate temperatures in the range of 600 to 1100°C. By using triethylgallium and ammonia as precursor and hydrogen and/or nitrogen as transport gases, we have observed a strong influence of molecular hydrogen on the deposition rate and the structural properties of epitaxial GaN. By elastic recoil detection analysis and thermal desorption measurements we were able to determine the total concentration of nitrogen, hydrogen and carbon in the bulk material. Isotope substitution of hydrogen by deuterium in the H₂ carrier gas did not give rise to a noticeable deuterium incorporation, showing that the sources for hydrogen are the metalorganic precursor, ammonia or reaction products of both. Once incorporated, thermally activated hydrogen effusion from n-type GaN occurs with an activation energy of more than 3.9 eV. With the help of mass spectrometry we established hydrogen effusion from heavily magnesium-doped (2 at%) GaN at temperatures between 600 and 700°C, which is the temperature range used for acceptor activation.