The annealing effects of Mg-doped GaN epilayers capped with SiO2 layers

We have investigated the annealing effect of Mg-doped GaN epilayers capped with SiO2 layer. Each of the Mg-doped GaN epilayers with and without SiO2 w as annealed at temperatures of 850, 900, and 950 degrees C after growth. Th e Van der Pauw technique and photoluminescence (PL) were used to evaluate t he changes in their electrical and optical characteristics. The SiO2 cappin g layers were removed by chemical etching after heat treatment. The hole co ncentration of the GaN:Mg epilayers capped with SiO2 after annealing is muc h higher than that of the layer annealed without SiO2 at any temperatures. But, the two types of epitaxial layers show very similar concentration chan ge with variation of the annealing temperature. The electrical resistivitie s as well as the hole concentration of the epilayers capped with SiO2 is mu ch lower than that of the layers annealed without SiO2 at any temperatures and the two types of epitaxial layers show very similar resistivity changes with the variation of annealing temperature. The luminescence intensity of the GaN:Mg epilayers capped with SiO2 measured by PL at both RT and 10 K i s higher than that of the epilayers annealed without SiO2 is very similar t o the data of hole concentration, the intensity of the epilayers annealed w ithout SiO2 capping decreases continuously with the increase of the anneali ng temperature which is different from the hole concentration. Judging from these results, it can be concluded that the SiO2 cap layer plays an import ant role in protecting the out-diffusion of cracked Mg from MgH complex dur ing annealing at temperatures of 850, 900, and 950 degrees C. It is also po ssible to conclude that the cracked Mg is still out-diffused from the GaN:M g epitaxy during annealing at temperatures 850, 900, and 950 degrees C in s pite of the SiO2 cap layer. (C) 2000 Elsevier Science B.V. All rights reser ved.