▎ 摘　　要

In graphene, band gap opening and tuning are important technological challenges for device applications. Various techniques have been suggested to this technologically complicated problem. Here, we present an ab initio study on the band gap opening in graphene through vacancy, adding impurity atom in the vacancy and substitutional co-doping. In the case of graphene with single vacancy a direct band gap of similar to 1 eV is obtained. This is a spin polarized state. The graphene system with two monovacancies gives rise to an effective indirect band gap (pseudo gap) of similar to 1 eV. The graphene substitutionally doped with B and N is co-doped (tri-doped) with S. This tri-doped graphene has turned into a semiconductor (band gap similar to 1 eV). These graphene semiconductors are better than the other semiconductor because of the presence of massless Dirac fermions in addition to normal electrons. This will have lot of application in device industry compared to a pristine graphene because of the presence of a gap and Dirac fermions. This type of band gap opening, with this type of defects and impurities, we are reporting for the first time.