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

Optical absorption properties of n-type In-doped ZnO films were investigated by spectroscopic ellipsometry for varying carrier concentration. The fundamental optical band gap (E-0) edge of the compound showed a blueshift below the carrier concentration n(0)=5x10(19) cm(-3), which can be explained in terms of the Burstein-Moss band-filling effect. An abrupt jump of the E-0 edge from blue- to redshift was observed as the carrier concentration increased beyond n(0). It is interpreted as due to a merging of the donor and conduction bands of the compound near n(0). The redshift increases quite linearly with the carrier concentration, reaching 600 meV for n=1.2x10(20) cm(-3). Such linear increase is interpreted as mainly due to a band gap narrowing caused by impurity-induced potential fluctuations. (C) 2001 American Institute of Physics.