Kinetics of low-temperature activation of acceptors in magnesium-doped gallium nitride epilayers grown by metal-organic vapor-phase epitaxy

摘要

The annealing process of magnesium-doped gallium nitride (GaN:Mg) epilayers grown by metal-organic vapor-phase epitaxy was investigated by in situ measurements of electrical transport properties. The resistivity ρ and the Hall effect were studied as functions of time and temperature in the range of 20-600℃. A time-dependent p-type conductivity was observed at temperatures as low as 350℃. Activation energy of about E_(act) = 1.5 eV was found for the magnesium acceptor (Mg) from the isothermal measurements of ρ(t) kinetics in the range of 350-550℃. This value corresponds well to the theoretical prediction for the thermal dissociation of magnesium-hydrogen complexes (Mg-H). The annealing at temperatures higher than 600℃ leads obviously to the activation of Mg acceptors, but the final resistivity of the sample is higher than the result obtained after annealing at 520℃. The ionization energy of electrically active Mg acceptor level of about E_A=170 meV was found from the temperature dependences of the resistivity ρ(T).