| III-Nitride semiconductor epitaxial thin films generally have a very high density of dislocations (of the order of 1010 cm −2) and other defects. The purpose of this study is to investigate the energetics of nitride film growth by plasma enhanced molecular beam epitaxy (PEMBE), which is aimed at reducing defects and improving AlN and GaN film quality.; The characteristics of the electron cyclotron resonance (ECR) plasma source used in the growth were fully explored. A method was developed to achieve tunable mono-energetic ion beams, and the influences of adding inert gases on the plasma properties were measured. These properties were used in the growth to study the plasma influence on the film quality.; The thermochemistry of AlN PEMBE growth was then investigated, including the reactants surface lifetime, the sticking coefficient, the growth rate, the free evaporation rate and the energy barrier, and the plasma influence on the evaporation, etc. It was found that GaN growth temperature is limited by the rapid decomposition, while for AlN, the growth temperature is limited by the finite surface lifetime (or the sticking coefficient) of aluminum. Thus, a temperature window exists between the highest growth temperature and the decomposition temperature of AlN. A post-growth anneal in this window can enhance the annihilation of defects. This results in a reduction of the dislocation density in the film by two orders of magnitude.; With the high quality GaN and AlN films, a graded structure consisting of n-GaN/AlxGa1−xN/metal was developed for the electron emission study, by utilizing the small electron affinity of AlN. The scheme was developed to grow a composition-graded AlxGa 1−xN (x: 0 → 1) thin film on top of n-type GaN. The abrupt band offset at the GaN/AlN interface is distributed in a thin layer of Al xGa1−xN with a smooth graded electron affinity, which is predicted to enhance the injection and transportation of electrons to the AlN surface, and then emit them into the vacuum. |
