Role of excited nitrogen species in the growth of GaN by RF–MBE

Optical emission spectroscopy (OES) was used with the combinatorial growth method to investigate the behavior of excited nitrogen species in the growth of gallium nitride (GaN) using radio-frequency molecular beam epitaxy (RF–MBE). To determine the amounts of each excited nitrogen species in the nitrogen plasma, the integrated OES intensity (IOI) method was proposed. The IOI measurements revealed the following: more nitrogen ions (N2+) were produced at the lower inlet pressure of nitrogen, the productivity of nitrogen atoms (N) and excited nitrogen atoms (N*) had an optimum value at some inlet pressure, whereas the productivity of excited nitrogen molecules (N2*) saturated as the inlet pressure increased. The combination of the IOI measurement and the combinatorial growth of GaN showed that not only N and N*, but also the long-lifetime A3Σu+ state of N2* contributed to GaN growth using RF–MBE.