Comparison of excited nitrogen sources for molecular-beam-epitaxy GaN growth: Radio frequency and electron cyclotron resonance plasma sources

Abstract

A comparative study of electron cyclotron resonance (ECR) and radio frequency (rf) plasma as a nitrogen source for molecular-beam epitaxy GaN was carried out. The effects of differences in the excited nitrogen species on the optical signals during GaN growth were investigated by 77 K photoluminescence (PL). For epitaxial layers grown at optimum V/III ratio using ECR and rf plasma, the PL spectra were dominated by near band-edge emission at 3.47 eV. However, when the V/III ratio was less than the optimum V/III ratio, a broad emission band at about 3.2–3.3 eV was observed in the PL spectrum for the GaN epilayer grown using rf plasma, while in the case of growth using ECR plasma, a deep level emission at about 2.2 eV appeared. These characteristics in PL spectra can used to identify differences in the chemical species in the nitrogen plasma.