We have investigated chemical, electrical and optical properties of Mg-doped GaN surfaces subjected to a high-temperature anneal. X-ray photoelectron spectroscopy (XPS) showed that Ga2p peaks were clearly detected at the SiO_2/p-GaN surface after the annealing at 1000 ℃, in addition to the Si and O peaks originating from SiO_2surface. This indicated that the out-diffusion of Ga atom was induced by high-temperature anneal. After removing the SiO_2 film, we found a significant segregation of Mg atoms near the p-GaN surface with the Mg-doping of 1×10~(19)cm~(-3). For the as-grown sample with the Mg-doping of 2×10~(19)cm~(-3), a broad PL peak at around 3.1eV was detected in addition to a weak band-edge emission. After the annealing, a new peak appeared at around 2.8 eV, of which the peak position is very close to the so-called blue luminescence (BL) often observed in the highly Mg-doped GaN. On the other hand, different PL spectra were observed for the sample with the Mg-doping of 3×10~(18)cm~(-3) before and after the annealing, indicating that the formation of deep level is dependent on the Mg density and annealing condition.%Mgドープ量の異なるGaN表面にSiO_2保護膜を形成し，1000-1100℃の高温でアニールを行い，アニール後のGが表面の化学的特性，光学的特性を評価した．保護膜を形成しているのにもかかわらず，高温アニール中にG劇表面から，Gaが外方拡散することが分かった．また高Mgドープ試料では，アニール後のGaN表面にMg偏析が確認された．PL測定から，高温アニール後のMgドープGaN表面に深い準位が新たに形成され，Mgドープ量が高いほど．高密度の深い準位が生成することが分かった．また，深い準位の発光スペクトルのピーク位置および形状はMgドープ量により大きく異なり．形成される深い準位の成因は，Mgドープ量によって異なる可能性があることが分かった．
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