  Narrow bandgap and its tuning are important aspects of materials for their
technological applications. In this context group IV VI semiconductors are one
of the interesting candidates. In this paper, we explore the possibility of
bandgap tuning in one of the family member of this family GeSe by using
isoelectronic Pb doping. Our study is first principles based electronic
structure calculations of GePbSe. This study reveals that the Ge-p and Se-p
states are strongly hybridized in GeSe and shows a gap in the DOS at Ef in
GeSe. This gap reduces systematically with simultaneous enhancement of the
states in the near Ef region as a function of Pb doping. This leads tuning of
the indirect bandgap in GeSe via Pb doping. The results of the indirect bandgap
decrement are consistent with the experimental findings. We propose a mechanism
where the electrostatic effect of dopant Pb cation could be responsible for
these changes in the electronic structure of GeSe.
