Study of Bandgap Energies of Cu(In,Ga)Se2Thin Films Grown by a Sequential Evaporation Method Using Piezoelectric Photothermal Spectroscopy

• DOI: 10.7567/jjap.51.07ga07
• Publication Date: 2013-12-21T12:19:07Z
• Authors: Takayuki Mori; Yutaro Motono; Wen Ding; Atsuhiko Fukuyama; Toshiyuki Yamaguchi; Tetsuo Ikari
• Keywords: 0103 physical sciences; 02 engineering and technology; 0210 nano-technology; 01 natural sciences

By using a sequential evaporation method, Cu(In,Ga)Se2 (CIGS) thin films with a high Ga/(Ga+In) mole ratio were fabricated on Mo/soda-lime glass substrates. The bandgap energy (E g) estimated by the photoreflectance (PR) and piezoelectric photothermal (PPT) methods shifted to the higher photon energy side with increasing Ga/(Ga+In) mole ratio. Although PR signals could not be observed, the PPT method could determine E g even for high Ga/(Ga+In) mole ratio samples. A broad photoluminescence peak originating from band-to-band or impurity level was also observed for all samples. The present experimental results imply that the Ga/(Ga+In) mole ratio of CIGS thin films can easily be controlled by a sequential evaporation method, and that the PPT method is a powerful method for determining the E g of low crystallinity samples.