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 was annealed at temperatures of 850, 900, and 950 °C after growth. The Van der Pauw technique and photoluminescence (PL) were used to evaluate the changes in their electrical and optical characteristics. The SiO₂ capping layers were removed by chemical etching after heat treatment. The hole concentration of the GaN:Mg epilayers capped with SiO₂ after annealing is much higher than that of the layer annealed without SiO₂ at any temperatures. But, the two types of epitaxial layers show very similar concentration change with variation of the annealing temperature. The electrical resistivities as well as the hole concentration of the epilayers capped with SiO₂ is much 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 is higher than that of the epilayers annealed without SiO₂ is very similar to the data of hole concentration, the intensity of the epilayers annealed without SiO₂ capping decreases continuously with the increase of the annealing temperature which is different from the hole concentration. Judging from these results, it can be concluded that the SiO₂ cap layer plays an important role in protecting the out-diffusion of cracked Mg from MgH complex during annealing at temperatures of 850, 900, and 950 °C. It is also possible to conclude that the cracked Mg is still out-diffused from the GaN:Mg epitaxy during annealing at temperatures 850, 900, and 950 °C in spite of the SiO₂ cap layer.