Beryllium doped p-type GaN grown by metal-organic chemical vapor deposition

The authors report on the growth of Be-doped p-type GaN epilayers by metal-organic chemical vapor deposition (MOCVD). The electrical and optical properties of the Be-doped GaN epilayers were studied by Hall-effect measurements and photoluminescence (PL) spectroscopy. The PL spectra of Be-doped GaN epilayers exhibited two emission lines at 3.36 and 2.71 eV, which were absent in undoped epilayers. The transition at 3.36 eV was assigned to the transition of free electrons to the neutral Be acceptor, Be⁰. The transition at 2.71 eV was assigned to the transition of electrons bound to deep level donors to the Be⁰ acceptors. Three independent measurements: (a) resistivity vs. temperature, (b) PL peak positions between Be doped and undoped GaN and (c) activation energy of 2.71 eV transition all indicate that the Be energy level is between 120 and 140 meV above the valence band. This is about 20-40 meV shallower than the Mg energy level (160 meV) in GaN. It is thus concluded that Be could be an excellent acceptor dopant in nitride materials.