GROWTH OF GALLIUM NITRIDE BY ELECTRON-CYCLOTRON-RESONANCE PLASMA-ASSISTED MOLECULAR-BEAM EPITAXY - THE ROLE OF CHARGED SPECIES

The role of ionic and nonionic excited species of nitrogen in the growth of GaN thin films by electron-cyclotron resonance (ECR) plasma-assisted molecular-beam epitaxy has been investigated. It was found that the kinetics of film growth is significantly afected by the microwave power in the ECR discharge. Specifically, a transition from the island to a layer-by-layer and, finally, to a three-dimensional growth has been observed as a function of power. These morphological changes are accompanied by degradation of the electrical and luminescence properties, a result attributable to increased native defects and impurities. Secondary-ion-mass spectroscopic (SIMS) analysis indicates that impurity levels in the films increase with the plasma power levels used during the growth. To study the relative role of ion-induced native defects in these films, strategies for charged species extraction were developed by using an off-axis solenoid to modify the magnetic environment during growth. Films grown under a reduced ionic/excited neutral ratio environment show marked improvement in the electrical and luminescence properties. These data, together with SIMS analysis, indicate that observed improvements in these films are due to a reduction of native defects and not impurities.