Large and abrupt optical band gap variation in In-doped ZnO

Abstract

Optical absorption properties of n-type In-doped ZnO films were investigated by spectroscopic ellipsometry for varying carrier concentration. The fundamental optical band gap (E0) edge of the compound showed a blueshift below the carrier concentration n0=5×1019 cm−3, which can be explained in terms of the Burstein–Moss band-filling effect. An abrupt jump of the E0 edge from blue- to redshift was observed as the carrier concentration increased beyond n0. It is interpreted as due to a merging of the donor and conduction bands of the compound near n0. The redshift increases quite linearly with the carrier concentration, reaching 600 meV for n=1.2×1020 cm−3. Such linear increase is interpreted as mainly due to a band gap narrowing caused by impurity-induced potential fluctuations.