Enhanced hole concentration through Ga doping and excess of Mg and thermoelectric properties of p-type Mg2(1+z)(Si0.3Sn0.7)1−yGay

► Element Ga is confirmed to be an effective p-type dopant in Mg2Si based materials. ► The excess of Mg largely increases the hole density of Mg2Si0.3Sn0.7. ► The increase in hole density by excess Mg is mainly due to antisite defects MgSi. ► The doping of Ga and excess of Mg do not have obvious effect on the band structure.